Merge pull request 'v0.28.0 (#46): per-region stats — area×population-weighted-median Nation.stats (PR 1 of 2)' (#47) from feat/46-region-stats into master

- shared: 8 MarkerTypes + MARKER_TYPE_INFO (label/color/glyph); MapMarker;
  GameState.markers (required, [] at init); TurnResult.markers {add,remove};
  MarkerSpec/MarkerInfo; FNV-1a 4-char markerId; MAX_MARKERS=400.
- data: new public/region-centroids.json (1,800 anchors = largest-part centroid
  + spread ~0.1x min-bbox) built by new idempotent scripts/build-region-centroids.mjs.
- server: regions.ts centroid loader (public/ then dist/); engine applyTurnResult
  marker ops (remove -> owner-recompute -> add, jitter, cap, never throws);
  prompt documents the contract; buildUserPrompt carries markers; stub marker-free.
- client: WorldMap symbol layer rendered as canvas per-type icons (glyph CDN dead);
  hover tooltip shows name; click focuses owning nation.
- tests: 168 -> 189 (centroids script, regions centroids, db legacy, engine markers).

AGENTS.md

@@ -28,13 +28,17 @@ renders territorial ownership; the whole thing persists to SQLite and streams ov
 - Backend: Node 22 + Express — one process serving the built client, `/api` (REST), and `/sse`
 - Persistence: `better-sqlite3` (one row per game, full `GameState` as JSON)
 - Map: MapLibre GL (`maplibre-gl`) — remote OpenFreeMap `dark` basemap + a **sub-national**
-  choropleth from `public/regions.geo.json` (1,796 sub-regions; feature `id` = `<ISO_A3>-<nn>`,
+  choropleth from `public/regions.geo.json` (1,800 sub-regions; feature `id` = `<ISO_A3>-<nn>`,
   `properties.parent` = the country's ISO_A3). Ownership is at **region-key** granularity
   (v0.19, #16 P1): every sub-region is addressed by a stable key from
   `public/region-keys.json`, `Nation.territory` holds those keys, and each sub-region is
   colored by its own owner. Since v0.21 (#16 P2) the LLM moves *individual* sub-regions
   across shared land borders (frontier-biased transfers, verified with the `getNeighbours`
-  function-calling tool) instead of whole countries.
+  function-calling tool) instead of whole countries. Since v0.25 (#31) the old RU-ARK
+  mega-region is split into the mainland (`RU-ARK`, key unchanged) plus the New Earth
+  (`RU-ARK-NE`) and Severnaya Zemlya (`RU-ARK-SZ`) island groups; since v0.26 (#41) the
+  mainland's 28-part Arctic-coast band is further re-partitioned into Pechora (`RU-PEO`)
+  and Yamal (`RU-YAM`) (the 5-part lat < 68 core stays `RU-ARK`/`arkhangel-sk-lhbk`).
 - The LLM client is a thin OpenAI chat-completions wrapper over native `fetch` with an
   **injectable transport** (mirrors `mesh-bot/src/llm`), with two entry points: plain
   `chat()` and `chatWithTools()` — a bounded OpenAI function-calling loop (max 6 tool
@@ -52,35 +56,44 @@ history/
 ├── eslint.config.js        # flat config (ESLint 9)
 ├── tsconfig.json           # strict; aliases @/ → src/, @shared/ → shared/
 ├── vite.config.ts          # dev server + proxy /api,/sse → :4321; @ / @shared aliases
-├── vitest.config.ts        # unit tests (server/**/*.test.ts + scripts/**/*.test.ts; 151 tests)
+├── vitest.config.ts        # unit tests (server/**/*.test.ts + scripts/**/*.test.ts; 225 tests)
 ├── playwright.config.ts    # deterministic e2e (webServer runs npm run dev, LLM_STUB=1)
 ├── index.html
 ├── presets/                # 5 scenario JSON files + index.json (manifest)
 ├── public/
 │   ├── countries.geo.json  # 177 countries, id=ISO_A3 (input to the region generator)
-│   ├── regions.geo.json    # 1,796 sub-regions, id=<ISO_A3>-<nn>, parent=ISO_A3 (the choropleth)
-│   ├── region-keys.json    # feature id -> region key, 1,796 entries (the ownership/LLM address space, #16 P1)
-│   └── region-adjacency.json # region key -> bordering region keys, 1,796 entries (the getNeighbours data, #16 P2)
+│   ├── regions.geo.json    # 1,800 sub-regions, id=<ISO_A3>-<nn>, parent=ISO_A3 (the choropleth)
+│   ├── region-keys.json    # feature id -> region key, 1,800 entries (the ownership/LLM address space, #16 P1)
+│   ├── region-adjacency.json # region key -> bordering region keys, 1,800 entries (the getNeighbours data, #16 P2)
+│   ├── region-centroids.json # region key -> {lat,lon,spread} anchor for map markers, 1,800 entries (#44)
+│   ├── region-geo.json     # region key -> {area (km²), population}, 1,800 entries (the area×population weighting for per-region stats, #46)
+│   └── ne-admin0-pop.json  # ISO_A3 -> admin-0 POP_EST, 249 codes (the committed population SOURCE for region-geo.json — a small derived table, the 13 MB Natural Earth source is NOT committed, #46)
 ├── scripts/                # the geo/manifest data pipeline — .mjs (turf allowed HERE only;
 │   │                       #   never imported by .ts): generate → coarsen → cleanup → smooth →
-│   │                       #   fill-gaps → build-region-keys → build-region-adjacency
-│   └── *.test.ts           # turf-free vitest tests pinning the dataset + both manifests
+│   │                       #   fill-gaps → split-arkhangel → split-arkhangel-band → build-region-keys
+│   │                       #   → build-region-adjacency → build-region-centroids → build-region-geo
+│   │                       #   (build-region-geo reads the COMMITTED ne-admin0-pop.json; that small
+│   │                       #   table is distilled once from the 13 MB Natural Earth admin-0 source by
+│   │                       #   extract-admin0-pop.mjs — the raw source is never committed, #46)
+│   └── *.test.ts           # turf-free vitest tests pinning the dataset + the manifests
 ├── shared/                 # NO runtime deps — the single source of truth
 │   ├── types.ts            #   domain types (Nation, GameState, RoundItem, Preset, …)
 │   └── protocol.ts         #   LLM TurnResult schema (incl. `unowned`, v0.22 #16 P3, and
-│                           #     `nationOps`, v0.23 #16 P4a) + AddAction/AddDiplomacy/RemoveQueueItem/
+│                           #     `nationOps`, v0.23 #16 P4a; v0.24 #16 P4b) + AddAction/AddDiplomacy/RemoveQueueItem/
 │                           #     Jump + NationOp confirm/reject request types + pure helpers
+│                           #     (incl. per-region stats, v0.28 #46: weightedMedian / deriveNationStats /
+│                           #     seedRegionStats / migrateRegionStats)
 ├── server/
 │   ├── index.ts            # Express: /api/* (health|action|diplomacy|queue/remove|jump|advisor|
 │   │                       #   nation-op/confirm|nation-op/reject|games|map|presets), /sse/:id; reads
 │   │                       #   PORT/LLM_*/DATA_DIR
-│   ├── engine.ts           # pure: prompts / parse+validate / applyTurnResult (sole-ownership + no-man's-land releases, v0.22 #16 P3) / runTurn (tool path + plain fallback) / getNeighbours tool + executor / playerFrontier / queue ops / advisor / nation-op ops (resolveNationRef / applyNationOp / confirmNationOp / rejectNationOp, v0.23 #16 P4a)
+│   ├── engine.ts           # pure: prompts / parse+validate / applyTurnResult (sole-ownership + no-man's-land releases, v0.22 #16 P3; per-region stats maintenance + derived recompute, v0.28 #46) / runTurn (tool path + plain fallback) / getNeighbours tool + executor / playerFrontier / queue ops / advisor / nation-op ops (resolveNationRef / freshNationId / NEW_NATION_STATS / applyNationOp rename+split+merge / confirmNationOp / rejectNationOp, v0.23 #16 P4a; v0.24 #16 P4b)
 │   ├── llm.ts              # LlmClient: chat() + chatWithTools() (bounded function-calling loop), injectable transport, retry+backoff, logging + env config
-│   ├── regions.ts          # turf-free region-key data access: load manifest/geo/adjacency (public/ then dist/), country→keys expansion, reference table, neighboursOf/hasAdjacency
+│   ├── regions.ts          # turf-free region-key data access: load manifest/geo/adjacency/centroids/geo-manifest (public/ then dist/), country→keys expansion, reference table, neighboursOf/hasAdjacency, centroidOf/hasCentroids, geoOf/hasGeo (#46)
 │   ├── stub.ts             # deterministic LLM transport (tests/e2e): one frontier conquest per turn + ADVISOR_MARKER
 │   ├── map.ts              # GameState → RegionMap (region key → owner + stable color)
 │   ├── presets.ts          # load preset JSON files from disk
-│   ├── db.ts               # SQLite open/save/load
+│   ├── db.ts               # SQLite open/save/load (+ legacy regionStats migration on load, v0.28 #46)
 │   └── *.test.ts           # unit tests (vitest)
 └── src/
     ├── App.tsx             # screen router (home → pick → game) + manual hash router (#/game/<id>); owns game/regions/advisors/busy
@@ -96,7 +109,7 @@ history/
         ├── WorldMap.tsx     # MapLibre basemap + choropleth + click→dossier + hover tooltip + player highlight
         ├── NationPanel.tsx  # a nation's stats/territory/diplomacy dossier
         ├── ActionPanel.tsx  # tabs: Action / Diplomacy / Advisor + pending-queue list (per-item trash button + confirm dialog) + "Jump forward" + "Nation proposals" trigger (v0.23 #16 P4a)
-        ├── NationOpDialog.tsx # review LLM-proposed nation ops (rename/split/merge) — confirm (editable rename) or reject (v0.23 #16 P4a)
+        ├── NationOpDialog.tsx # review LLM-proposed nation ops (rename/split/merge) — confirm (editable rename/merge name, split successor radio) or reject (v0.24 #16 P4b)
         ├── EventFeed.tsx    # scrolling event log (newest first)
         ├── FloatingWindow.tsx # the HUD window primitive — free-floating (draggable, position persisted), or `pinned` (fixed top-center bar), or `dock`ed (full-height left/right column); renders dock controls when `onDockChange` is set
         ├── StatBar.tsx
@@ -110,11 +123,15 @@ history/
 | `npm run dev` | Express on :4321 (tsx watch) + Vite on :5173 (proxies `/api`,`/sse`) concurrently |
 | `npm run build` | `vite build` (client → `dist/`) then `tsup server/index.ts` → `server/dist/index.js` |
 | `npm start` | run the compiled server (`node server/dist/index.js`) on :4321 |
-| `npm test` | vitest unit tests (`server/` + `scripts/`; 151 tests) |
+| `npm test` | vitest unit tests (`server/` + `scripts/`; 225 tests) |
 | `npm run typecheck` | `tsc --noEmit` (strict) across src/server/shared/e2e/configs |
 | `npm run lint` | ESLint flat config |
 | `npm run e2e` | Playwright, fully deterministic (`LLM_STUB=1`); **runs in CI on every PR** (see below) |
-| `npm run build:region-keys` / `build:region-adjacency` | (re)generate the `public/region-keys.json` / `region-adjacency.json` manifests — deterministic + idempotent (byte-identical re-run) |
+| `npm run split:regions` | (re)apply the #31 Arkhangel'sk split (`RU-ARK` → mainland + `RU-ARK-NE` + `RU-ARK-SZ`) — idempotent no-op once applied |
+| `npm run split:regions:band` | (re)apply the #41 Arctic-coast-band split (`RU-ARK` mainland's 28-part lat ≥ 68 band → `RU-PEO` + `RU-YAM`) — idempotent no-op once applied |
+| `npm run build:region-keys` / `build:region-adjacency` / `build:region-centroids` | (re)generate the `public/region-keys.json` / `region-adjacency.json` / `region-centroids.json` manifests — deterministic + idempotent (byte-identical re-run) |
+| `npm run build:region-geo` | (re)generate `public/region-geo.json` (region key → area km² + population) from `regions.geo.json` + `region-keys.json` + the committed `ne-admin0-pop.json` — deterministic + idempotent (byte-identical re-run; #46) |
+| `npm run extract:admin0-pop` | one-time distillation of the 13 MB Natural Earth admin-0 source → the committed `public/ne-admin0-pop.json` (ISO_A3 → `POP_EST`, 249 codes); the raw source is never committed (#46) |
 | `docker compose up -d --build` | prod image on :4321, routed via Traefik at `history.dev.kkhost.pl` |
 
 **Local verification (before every PR):** `npm run typecheck` + `npm run lint` + `npm test` (unit) + `npm run build`. The full **e2e** suite (`npm run e2e`) is verified by **CI on every PR** (the Playwright config boots its own dev webServer with `LLM_STUB=1`) — locally you only need the four checks above; e2e is the CI source of truth.
@@ -188,25 +205,128 @@ history/
   "No man's land" tooltip sub-line) while a preset-unassigned key keeps the faint look ("No owner")
   — the distinction is decided by the client from `GameState.unowned` (via `regionFillStyle` /
   `unownedTooltipLabel`), never by the `RegionMap`, which only knows "owned" vs "absent". A fresh
-  game always starts with `unowned: []` (legacy SQLite rows load with it defaulted).
-- **Nation ops — “LLM proposes, player confirms” (v0.23, #16 P4a).** `TurnResult.nationOps` (required
-  in the schema) carries the LLM’s proposed **`NationOp`s** — a discriminated union of `rename` /
-  `split` / `merge`. `rename` is fully applied; `split` and `merge` are **declared shapes only**
-  (accepted and stored as pending, but a no-op until P4b implements them). Each op names its target
-  via `nationRef` — the LLM may use a nation’s **id or name**; `resolveNationRef` resolves id-first,
-  then a case-insensitive unique-name match, and returns `null` for an unknown or ambiguous ref (such
-  ops are dropped defensively in `validateNationOps`, never thrown). A turn’s ops are appended to
-  `GameState.pendingNationOps`, which is **never cleared on a turn commit** — pending proposals persist
-  across turns until resolved (like the action queue). The player then decides per op via
-  `POST /api/games/:id/nation-op/confirm` (`{index, edits?{name?}}`) or `.../nation-op/reject`
-  (`{index}`): `confirmNationOp` applies the op to a clone (a rename sets `Nation.name` to the edited
-  value or, failing that, the proposed `to`; id / territory / relations / `playerNationId` stay valid,
-  so a renamed player is re-named in place) and `rejectNationOp` just drops it — both splice by index
-  and bump `version` once (an invalid index → `null` → HTTP 400). The response is `{ game }` and the
-  server broadcasts a version-bumped SSE `state`, so every tab’s version-guarded `applyState` stays in
-  sync. The client lists the pending ops in a “Nation proposals” dialog (in the “Your move” panel) with
-  an editable rename name plus Confirm / Reject. The stub never proposes a nation op (`nationOps: []`),
-  so this path is covered by unit tests only (`server/engine.test.ts`).
+  game always starts with `unowned: []` (legacy SQLite rows load with it defaulted). Since v0.25
+  (#31) the 78-part RU-ARK mega-region is split into three features — mainland `RU-ARK` (its key
+  `arkhangel-sk-lhbk` is **unchanged**, so existing ownership is safe), `RU-ARK-NE` (New Earth /
+  Franz Josef Land, `new-earth-eikt`) and `RU-ARK-SZ` (Severnaya Zemlya,
+  `severnaya-zemlya-awqp`) — by the idempotent `scripts/split-arkhangel.mjs` stage (run between
+  `fill:regions` and `build:region-keys`, no-op once applied); the two island groups get their own
+  region keys and adjacency entries (New Earth is genuinely isolated → empty adjacency; Severnaya
+  Zemlya's islet rings touch the coarsened mainland ring, so it records one SZ↔mainland pair).
+  Since v0.26 (#41) the mainland's 28-part Arctic-coast band (centroid lat ≥ 68) is further
+  re-partitioned by the idempotent `scripts/split-arkhangel-band.mjs` stage (run between
+  `split:regions` and `build:region-keys`, no-op once applied) into Pechora (`RU-PEO`,
+  `pechora-qwhs`, 13 parts) and Yamal (`RU-YAM`, `yamal-gosw`, 15 parts) — a pure re-partition
+  (no geometry moved → the union is byte-identical) that keeps `RU-ARK`'s id/name/key
+  `arkhangel-sk-lhbk` stable and inserts the two new features immediately after `RU-ARK-SZ`; the
+  5-part lat < 68 core stays `RU-ARK` (a single ~305k km² polygon — splitting it needs turf
+  clipping, not a pure re-partition).
+- **Nation ops — “LLM proposes, player confirms” (v0.23, #16 P4a; v0.24, #16 P4b).**
+  `TurnResult.nationOps` (required in the schema) carries the LLM’s proposed **`NationOp`s** — a
+  discriminated union of `rename` / `split` / `merge`, all three of which are now applied on confirm
+  (P4b implemented split/merge). Each op names its target via `nationRef` — the LLM may use a
+  nation’s **id or name**; `resolveNationRef` resolves id-first, then a case-insensitive
+  unique-name match, and returns `null` for an unknown or ambiguous ref (such ops are dropped
+  defensively in `validateNationOps`, never thrown). A turn’s ops are appended to
+  `GameState.pendingNationOps`, which is **never cleared on a turn commit** — pending proposals
+  persist across turns until resolved (like the action queue). The player then decides per op via
+  `POST /api/games/:id/nation-op/confirm` (`{index, edits?{name?, playerPart?}}`) or
+  `.../nation-op/reject` (`{index}`): `confirmNationOp` applies the op to a clone — **rename** sets
+  `Nation.name` to the edited value or, failing that, the proposed `to` (id / territory / relations /
+  `playerNationId` stay valid, so a renamed player is re-named in place); **split** (the parent
+  must resolve and have ≥2 named parts, else a no-op) partitions the parent’s region-key territory
+  into new nations in parts order — each new nation gets a fresh id (`freshNationId`: first free of
+  `n1`, `n2`, …) and the baseline `NEW_NATION_STATS` (not a copy of the parent’s), plus a copy of
+  the parent’s relations; a key named by several parts goes to the first, and the parent’s
+  unclaimed keys go to part 0 (in territory order), so sole ownership holds and nothing is
+  orphaned; if the parent was the player’s nation, `playerNationId` moves to the part chosen by
+  `edits.playerPart` (clamped into range, default 0), which also receives `edits.name`; **merge**
+  (every ref must resolve, ≥2 DISTINCT inputs, and the survivor must be one of them, else a
+  no-op) folds the inputs into the survivor, which keeps its id and its own stats, gains the
+  union of the inputs’ territories (the survivor’s keys first) and a union of their relations
+  (the survivor’s own view of a third party wins, else the first input’s), is renamed
+  `edits.name` → `into` → its own name, while the other inputs are removed and their ids dropped
+  from every remaining nation’s relations maps; if the player led a removed input,
+  `playerNationId` moves to the survivor. An op that is invalid at confirm time (an ambiguous ref,
+  …) is a no-op on the world but is still removed — and `rejectNationOp` just drops it; both
+  splice by index and bump `version` once (an invalid index → `null` → HTTP 400). The response is
+  `{ game }` and the server broadcasts a version-bumped SSE `state`, so every tab’s
+  version-guarded `applyState` stays in sync. The client lists the pending ops in a “Nation
+  proposals” dialog (in the “Your move” panel): a rename and a merge show an editable name field
+  (the merge also highlights the survivor among the input chips); a split lists each part (name +
+  proposed region count) with a successor radio that appears only when the parent is the player’s
+  own nation (preselected part 0 — the choice is always valid). The system prompt documents all
+  three op shapes as a proposal queue (at most 1–2 per turn, each narrated in events). The stub
+  never proposes a nation op (`nationOps: []`), so this path is covered by unit tests only
+  (`server/engine.test.ts`).
+- **Map markers (v0.27, #44) — LLM-placed named points, region-anchored, canvas-icon rendered.**
+  The LLM can place named **point markers** on the map each turn: eight `MarkerType`s
+  (`city, factory, army, port, capital, fleet, rocket, gathering`; a **capital** is at most one
+  per nation, a **gathering** a political/social mass event that can enable a non-military
+  takeover). `TurnResult.markers = { add: MarkerSpec[]; remove: string[] }` (both required,
+  default `[]`; `MarkerSpec = { type, name, regionKey }`). A marker's stable `id` is the FNV-1a
+  32-bit hash of `` `${type}\u0000${name}\u0000${regionKey}` `` rendered as four lowercase
+  base-26 characters (mirroring the region-key scheme) — so a **re-add is idempotent** and a
+  **remove is unambiguous** (by id). `GameState.markers: MapMarker[]` is required (`[]` at game
+  creation; a legacy SQLite row without the field loads as `[]` — additive, never wipes).
+  `applyTurnResult` handles markers **after** territory claims: (1) remove by id (absent id →
+  no-op); (2) **recompute every surviving marker's `ownerNationId` from the final post-claim
+  ownership** — a marker always follows its region (a captured region follows its new owner; a
+  region released to no man's land, or a key with 0 or 2+ owners, becomes `null`); (3) add — each
+  new spec is placed at its region's centroid (from `public/region-centroids.json`, injected via
+  the optional `centroidOf` param on `applyTurnResult`) plus a deterministic per-axis jitter
+  (`spread ≈ 0.1 × the largest part's smallest bbox dimension`, so multiple markers of one region
+  scatter instead of stacking), owned by the region's post-turn owner, stamped with the acting
+  turn. Adds are **dropped, never thrown**, when the region key is unknown or has no centroid,
+  when the id already exists, or beyond the hard cap `MAX_MARKERS = 400`. The system prompt
+  documents the field + types + placement rules; `buildUserPrompt` carries the current markers
+  (as `MarkerInfo[]`) so the model can reference their ids in `remove`; a marker add/remove makes
+  a turn "meaningful". **Rendering is canvas-generated per-type ICON images, NOT text labels**
+  (`src/components/WorldMap.tsx`): every external glyph/font endpoint is a dead 404 (OpenFreeMap's
+  `fonts/{stack}/{range}.pbf` and `demotiles.maplibre.org/font/…`) and the OFM dark basemap only
+  renders because it is **raster** (labels baked into the tiles) — there is no working vector
+  font, so markers are drawn as self-contained, offline, deterministic per-type icons
+  (`drawMarkerIcon`: distinct shape per type, filled with the type color, outlined for legibility),
+  registered as named `ImageData` images that survive `styledata`. The marker **name shows in the
+  hover tooltip** (not a persistent on-map label), and **clicking a marker focuses its owning
+  nation's dossier**. There are **no separate marker event handlers** — MapLibre's per-layer event
+  delegates fire independently (no `stopPropagation`), so the region hover/click handlers instead
+  `queryRenderedFeatures` the marker layer under the cursor and act on the marker when present.
+  The **stub is marker-free** (`markers: { add: [], remove: [] }`) — e2e (CI, `LLM_STUB=1`) is
+  unaffected and the marker path is unit-tested only (`server/engine.test.ts`,
+  `scripts/region-centroids.test.ts`, `server/regions.test.ts`, `server/db.test.ts`).
+- **Per-region stats — `GameState.regionStats`, derived `Nation.stats` (v0.28, #46; PR 1 of 2 — the LLM lever is PR 2).**
+  Since v0.28 the four 0–100 stats live at **region-key** granularity: `GameState.regionStats`
+  (required; `{}` at game creation) maps each owned region key to its own `RegionStats`, and
+  `Nation.stats` is **derived** — the **area×population-weighted median** of the stats of the
+  regions the nation owns (`deriveNationStats`, pure in `shared/protocol.ts`). A region's weight
+  is `(area>0?area:1)×(population>0?population:1)` from the committed `public/region-geo.json`
+  manifest (1,800 entries; area in km² at 2dp, integer population) — which is built by
+  `scripts/build-region-geo.mjs` from `regions.geo.json` + `region-keys.json` + the committed
+  `public/ne-admin0-pop.json` (Natural Earth admin-0 `POP_EST`, 249 codes, one-time distilled by
+  `scripts/extract-admin0-pop.mjs`; each country's `POP_EST` is spread over its sub-regions
+  proportional to area by largest-remainder, so per-country totals are preserved exactly). A
+  released / 0-owner / 2+-owner key has **no** entry. A fresh game is seeded by
+  `seedRegionStats` (every owned region gets a **copy** of its owner's stats — identical values,
+  so the derived median equals the original and fresh-game numbers are unchanged). Legacy SQLite
+  rows are migrated once on load by `migrateRegionStats` (`db.load`, called without `geoOf` —
+  weight-invariant for the identical-value seed): a row that already has `regionStats` (v0.28+)
+  is returned **unchanged** (never recomputed on load → no drift), a legacy row is seeded +
+  recomputed (0-region guard keeps its stats). `applyTurnResult` takes an optional `geoOf`
+  (passed through `runTurn`; the jump route wires it via `hasGeo() ? (key) => geoOf(key) :
+  undefined`) and maintains the table inside the **load-bearing order events → relations →
+  territory → stateChanges → recompute → markers → nationOps**: a release deletes the key's
+  entry; a (re-)claim re-inits an absent entry as a copy of the gainer's current `stats`;
+  nation-level `stateChanges` (the only LLM lever for now — the prompt is **unchanged** in this
+  PR) write to `n.stats` **and** to every region the nation owns; then every nation with ≥1
+  entered region gets `stats` recomputed as its regions' weighted median (a 0-region — or no-
+  entered-region — nation keeps its directly-maintained `stats`, which is why the existing unit
+  and e2e assertions pass unchanged; without the geo manifest the recompute degrades to an
+  unweighted median, never throwing). The stub never touches per-region stats (`LLM_STUB=1`
+  e2e unaffected), and the path is unit-tested (`server/engine.test.ts`,
+  `server/protocol.test.ts`, `server/db.test.ts`, `server/regions.test.ts`,
+  `scripts/region-geo.test.ts`). **PR 1 of 2 — deliberately NOT deployed** (the user deploys
+  when PR 2, the per-region LLM lever, ships).
 - **Map click → dossier target (owner resolved from the RegionMap, by region key).**
   Clicking a sub-region does NOT open a popup — it switches the dossier to that sub-region's
   owning nation (`focusNation(ownerId, {name})` in `App.tsx`, which also records which region was
@@ -233,9 +353,9 @@ history/
   no man's land (it always returns `unowned: []` and ignores the payload's `unowned` field) — its
   one-conquest behavior is what the e2e assertions rely on, so the release/re-claim path is
   covered by unit tests only (`server/engine.test.ts`, `server/map.test.ts`). Since v0.23 (#16 P4a)
-  the stub also returns `nationOps: []` — it **never proposes** a nation op (rename/split/merge), so
-  the confirm/reject path is covered by unit tests only, mirroring the P3 approach; all e2e
-  assertions are unaffected. The stub answers plain `content` (never tool calls), so it naturally
+  the stub also returns `nationOps: []` — it **never proposes** a nation op (rename/split/merge;
+  still true since P4b implemented split/merge), so the confirm/reject path is covered by unit
+  tests only, mirroring the P3 approach; all e2e assertions are unaffected. The stub answers plain `content` (never tool calls), so it naturally
   bypasses the tool loop in a single round. Unit + e2e assertions rely on these exact values, so
   keep the stub deterministic.
 - **HUD layout.** The game screen is a full-viewport map (z-0) with `FloatingWindow` overlays. The
@@ -327,7 +447,8 @@ history/
   (works on `node:22-slim`/glibc). It's the sole `--external` in the tsup server bundle.
 - The `dist/` client is committed to the build output only; the `public/` data files
   (`regions.geo.json` — the choropleth — `region-keys.json` + `region-adjacency.json` — the
-  ownership/adjacency manifests — and `countries.geo.json`) are copied into `dist/` by Vite at
+  ownership/adjacency manifests — `region-centroids.json` — the marker anchors (#44) — and
+   `countries.geo.json`) are copied into `dist/` by Vite at
   build time, so the prod image serves them from `dist/` (no separate copy). The server's region
   loader (`server/regions.ts`) probes `public/` then `dist/` for the manifest pair, because the
   Docker image keeps only `dist/` (the v0.20 fix — before it, region-level ownership silently

CHANGELOG.md

@@ -2,6 +2,79 @@
 
 All notable changes to **History** are listed here, newest first.
 
+## v0.28.0 — 2026-10-15 00:12
+- **#46 (PR 1 of 2): per-region stats — a nation's four 0–100 stats become a *derived* aggregate.** Instead of storing `Nation.stats` as four independent per-nation numbers, they are now **derived** as the **area×population-weighted median** of the stats of the regions the nation owns. Each sub-region carries its own `RegionStats` in a new `GameState.regionStats: Record<regionKey, RegionStats>` table; a nation's displayed stats are the weighted median over its owned regions. This is the data foundation for the per-region LLM levers that land in **PR 2** — in this PR the LLM still only emits nation-level `stateChanges`, which are re-interpreted as applying to *all* of a nation's owned regions. A new `public/region-geo.json` manifest (area km² + population per region key) supplies the weighting. **Not deployed in this PR** — the production site updates when PR 2 ships (the change is additive and backward-compatible, so deferring the deploy is safe).
+  - **Data build (`scripts/`, turf-`.mjs` only; never imported by `.ts`).**
+    - `scripts/extract-admin0-pop.mjs` (`npm run extract:admin0-pop`) — **one-time** distillation of the 13 MB Natural Earth 1:10m admin-0 GeoJSON (a *source* file we do **not** commit) into the small committed `public/ne-admin0-pop.json` = `{ ADM0_A3 → max POP_EST }` (249 country codes, total 7,677,059,722). The 1:10m **admin-1** file the region generator uses carries no population, so the source is the **admin-0** `POP_EST` (a deliberate deviation, recorded here).
+    - `scripts/build-region-geo.mjs` (`npm run build:region-geo`) — builds `public/region-geo.json` = `{ regionKey → { area, population } }`: `area` = `@turf/area(finalFeature)/1e6` km² (2 dp); `population` = the parent country's `POP_EST` spread across its sub-regions **proportional to area via largest-remainder**, so every country's sub-regions sum **exactly** to its total (no rounding drift). Reads the committed `ne-admin0-pop.json` → fully reproducible in CI. **Deterministic + idempotent** (sorted keys; byte-identical re-run, pinned by the test). 1,800 entries; **total population 7,654,092,021** (the sum over the 177 repo countries).
+  - **Types (`shared/types.ts`, no runtime deps).** New `RegionStats = { military, economy, stability, population }` (0–100). `GameState.regionStats: Record<string, RegionStats>` is **required** (`{}` at game creation; a released / 0-owner / 2+owner region has **no** entry; a legacy SQLite row without the field is migrated on load, never wiped).
+  - **Pure helpers (`shared/protocol.ts`, no deps).**
+    - `weightedMedian(values, weights)` — sorts by value and returns the value at the first point the cumulative weight reaches half the total; non-finite/non-positive weights are excluded; empty / zero-total → 0. **Translation-invariant** (the median of identical values is that value — the invariant seeding and migration rely on).
+    - `deriveNationStats(regionKeys, regionStats, geoOf?)` — each stat is the weighted median over the nation's owned region keys; a region's weight is `(area>0?area:1)×(population>0?population:1)` (both fall back to 1 when the key has no geo entry, so missing geo degrades to a uniform median); a key with no `regionStats` entry is skipped; returns zero stats when no owned region has an entry (the caller's 0-region guard keeps `n.stats` in that case).
+    - `seedRegionStats(nations)` — seeds the table from nations: every owned key gets a **copy** of its owner's stats (first owner wins on a corrupt double-ownership), so a fresh nation's regions start identical (derived = seeded).
+    - `migrateRegionStats(state, geoOf?)` — **one-time** legacy migration: a row that already has `regionStats` is returned **unchanged** (no recompute on load → no drift); a legacy row (field absent) is seeded per region and each nation's stats recomputed (0-region guard). Never throws.
+  - **Server (`server/regions.ts`, turf-free).** Loads `region-geo.json` (probes `public/` then `dist/`) **optionally** — a missing/broken file degrades weighting to uniform (every region weight 1) while everything else keeps working. New `hasGeo()` and `geoOf(key)` accessors mirror the existing `hasCentroids`/`centroidOf`.
+  - **Server (`server/engine.ts`).** `applyTurnResult` gains an optional `geoOf` param and is reordered to: events → relations → **territory** → **stateChanges** → **recompute** → markers → nationOps.
+    - **Territory:** a **transferred** region **keeps its own** per-region stats (the conquest is what makes a nation's regions diverge); a **released** region's entry is **deleted** (no man's land carries none); a **re-claimed** region with no entry is **re-inited** to the gainer's current stats.
+    - **StateChanges (re-interpreted):** a nation-level `set`/`add` applies to `n.stats` **and** to every region the nation owns (clamped 0–100).
+    - **Recompute:** every nation's `stats` is re-derived via `deriveNationStats` (weighted by area×population when `geoOf` is present). Two guards: a **0-region** nation keeps its directly-maintained stats, and a nation **none of whose regions has an entry** keeps its stats too (avoids clobbering with zeros).
+    - `runTurn` threads the optional `geoOf` through to `applyTurnResult`.
+  - **Server (`server/index.ts`).** Game creation seeds `regionStats` via `seedRegionStats` **after** `expandCountriesToKeys` (so regions hold real keys) — a new game's derived stats equal its nation-level stats on turn 1. The `jump` route passes `geoOf: hasGeo() ? geoOf : undefined`.
+  - **Server (`server/db.ts`).** `load()` migrates a legacy row (regionStats absent) via `migrateRegionStats(state)` **without** `geoOf` (uniform weights — weight-invariant for the equal-value seeding, and avoids a `db`→`regions` import). v0.28+ rows load unchanged.
+  - **Prompt / client / stub unchanged.** `nationForPrompt`/`buildUserPrompt` still surface the (now derived) four stats; there is no per-region LLM lever yet (PR 2). The deterministic stub is unaffected (nation-level `stateChanges` flow through the re-interpretation; the median of identical values is that value, so e2e stat assertions hold).
+  - **Tests (189 → 225).** New `server/protocol.test.ts` (weightedMedian incl. translation-invariance / identical / zero / empty; deriveNationStats weighted vs uniform / skip-missing / zero / single / fallback-weight; seedRegionStats; migrateRegionStats v0.28+ no-op vs legacy / 0-region); `server/engine.test.ts` (transfer keeps region stats + aggregate blends, release deletes entry, re-claim re-inits, 0-region keeps stats, geoOf-weighted vs uniform recompute, nation-level change re-applies to regions, original not mutated); `server/db.test.ts` (legacy row → seeded + preserved stats; v0.28+ row loads unchanged); `server/regions.test.ts` (`hasGeo`/`geoOf` in dev + prod-`dist/` layouts, graceful degradation when absent); new `scripts/region-geo.test.ts` (1,800-entry key-set match, sorted, finite / ≤2dp area / integer population, total 7,654,092,021, per-country totals preserved vs admin-0, spot-checked values, byte-identical re-run).
+  - **Verification.** Typecheck, lint, **225 unit tests**, and the production build all pass (the build copies `region-geo.json` + `ne-admin0-pop.json` into `dist/` like the other manifests, so the prod container layout is covered). e2e is verified by CI on the PR (no local run).
+  - **Deploy:** **none** in this PR — the production site (`https://history.dev.kkhost.pl`) updates when **PR 2** ships. The change is additive + backward-compatible, so existing games migrate on load and no data wipe is needed.
+
+## v0.27.0 — 2026-10-14 22:34
+- **#44: the LLM can place named point markers on the map.** The model may now place up to a handful of named *point markers* per turn (a capital, city, factory complex, army deployment, port, fleet concentration, rocket launch site, or a political **gathering**), each anchored to a region key, persisted per game, and rendered on the choropleth as a MapLibre symbol layer.
+  - **Types (`shared/types.ts` + `shared/protocol.ts`).** Eight `MarkerType`s — `city, factory, army, port, capital, fleet, rocket, gathering` — with a shared `MARKER_TYPE_INFO` map (display label + color + glyph). A `MapMarker = { id, type, name, regionKey, lat, lon, ownerNationId, placedTurn }`; `GameState.markers: MapMarker[]` is **required** (`[]` at game creation, and a legacy SQLite row without the field loads as `[]` — additive, never wipes existing markers). `TurnResult.markers = { add: MarkerSpec[]; remove: string[] }` (both required, default `[]`); `MarkerSpec = { type, name, regionKey }`.
+  - **Stable ids (`shared/protocol.ts`).** A marker's `id` is the FNV-1a 32-bit hash of `` `${type}\u0000${name}\u0000${regionKey}` `` rendered as four lowercase base-26 characters (mirroring the region-key scheme). This makes a **re-add idempotent** (the same type+name+region never creates a second marker) and a **remove unambiguous** (by id).
+  - **Centroid data (`public/region-centroids.json`, new).** ~1,800 entries keyed identically to `region-keys.json`, each `{ lat, lon, spread }`: the anchor is the **centroid of the region's largest-area part** (a single representative point, not an average across disjoint parts), and `spread` ≈ **0.1 × that part's smallest bbox dimension** (in degrees). A new idempotent pipeline stage `scripts/build-region-centroids.mjs` (`npm run build:region-centroids`) regenerates it deterministically (byte-identical re-run, sha256-pinned by the test). The engine uses the centroid as the marker's base position and the `spread` to jitter multiple markers of one region around it (a deterministic per-axis FNV-1a-derived offset, so markers scatter instead of stacking).
+  - **Engine (`server/engine.ts`).** `applyTurnResult` processes markers **after** territory claims, in three steps: (1) remove by id (a listed-but-absent id is a no-op); (2) **recompute every surviving marker's `ownerNationId` from the final post-claim ownership** — a captured region follows its new owner, a region released to no man's land (or a key with 0 or 2+ owners) becomes `null` (a marker always follows its region); (3) add — each new spec is placed at its region's centroid (injected via a new optional `centroidOf` param) plus the per-axis jitter, owned by the region's post-turn owner, stamped with the acting turn. Adds are dropped (never thrown) when their region key is unknown / has no centroid, when the id already exists (idempotent re-add), or beyond the hard cap `MAX_MARKERS = 400` (later adds dropped). The system prompt documents the field, the eight types, and the placement rules; `buildUserPrompt` carries the current markers (as `MarkerInfo[]`) so the model can reference their stable ids in `remove`; `isMeaningful` treats a marker add/remove as a real world change.
+  - **Client (`src/components/WorldMap.tsx`).** A second GeoJSON source + a symbol layer sits above the choropleth. **Deliberate deviation from the original "name as a text label" design:** every external glyph endpoint is a dead 404 (OpenFreeMap's `fonts/{stack}/{range}.pbf` and `demotiles.maplibre.org/font/…`), and the OFM dark basemap only renders at all because it is **raster** (labels baked into the PNG tiles) — there is no working vector font. So markers are drawn as **self-contained, offline, canvas-generated per-type icons** (`drawMarkerIcon`: a distinct shape per type — circle / rounded-square / triangle / diamond / star / center-dotted circles / up-arrow — filled with the type color, outlined for legibility on the dark basemap), registered as named `ImageData` images that survive `styledata`. The marker **name is shown in the hover tooltip** (region name + owner chip + marker name) instead of a persistent on-map label, and **clicking a marker focuses its owning nation's dossier** (a marker's owner is its region's owner). There are no separate marker event handlers: MapLibre's per-layer event delegates fire independently (no `stopPropagation`), so the region hover/click handlers instead `queryRenderedFeatures` the marker layer under the cursor and act on the marker when present.
+  - **Stub (`server/stub.ts`) stays marker-free** — it returns `markers: { add: [], remove: [] }` — so the e2e suite (CI, `LLM_STUB=1`) is unaffected and fully deterministic; the full marker path is covered by unit tests only.
+- **Tests (168 → 189).** New `scripts/region-centroids.test.ts` (1,800 entries, key-set match, finite/world-bounds, each centroid inside its feature's bbox via turf-free coordinate iteration, spot-checked anchors, byte-identical re-run determinism); `server/regions.test.ts` (`hasCentroids`/`centroidOf` in dev + prod-`dist/` layouts, graceful degradation when absent); `server/db.test.ts` (legacy row → `markers: []`); and an `engine.test.ts` marker suite (valid add → id/position/owner/placedTurn, idempotent re-add, region-validity/centroid drops, the 400 cap, remove by id / no-op, owner-follows-region incl. release→null and re-claim, `buildUserPrompt`/system-prompt contract, `validateMarkerOps` raw cleaner, and the `runTurn` centroid wiring).
+- **Verification.** Typecheck, lint, **189 unit tests**, and the production build all pass (the build copies `region-centroids.json` into `dist/` like the other manifests, so it works in the prod container layout).
+- **Deploy:** manual `docker compose up -d --build` on the host — **no `down -v`** (markers are additive; legacy games load with `markers: []`).
+
+## v0.26.0 — 2026-10-14 19:24
+- **#41: the `RU-ARK` mainland's Arctic-coast band is re-coarsened into two new regions** — a pure re-partition of the existing polygon parts: no new geometry, no coordinate change (the feature union stays byte-identical). After #31 the mainland `RU-ARK` was a 33-part MultiPolygon; its 28-part band (parts whose centroid lat ≥ 68 — the Arctic-coast strip) is now split into:
+  - `RU-PEO` — Pechora (13 parts, ~37,678 km²) → new region key `pechora-qwhs`. The southwestern band (around the Pechora delta / Nenets border).
+  - `RU-YAM` — Yamal (15 parts, ~51,722 km²) → new region key `yamal-gosw`. The northeastern band (Yamal peninsula).
+  - The 5 remaining lat < 68 parts (the ~305,229 km² inland core) **stay `RU-ARK` and keep its id, name, and region key `arkhangel-sk-lhbk`** — ownership-safe, mirroring the #31 precedent. Splitting that core further requires geometry clipping (a turf-op), not a pure re-partition, and is left as a follow-up issue.
+  - **New pipeline stage** `scripts/split-arkhangel-band.mjs` (`npm run split:regions:band`), run between `split:regions` and `build:region-keys`: deterministic and **idempotent** (a second run is a no-op that writes nothing). It asserts the mainland is a 33-part MultiPolygon, selects the band as the 28 parts with centroid lat ≥ 68 (exactly 28, or it fails loudly), picks the two largest-area band parts as Voronoi anchors (the smaller-longitude one, `idx 1`, anchors the Pechora side), and assigns each band part to the nearer anchor by km-weighted centroid distance `hypot(Δlon·111.32·cos(midLat), Δlat·110.574)` (ties go west). The resulting partition is exactly PEO={1,4,5,9,11,12,13,14,16,17,18,20,22}, YAM={2,6,15,19,21,23,24,25,26,27,28,29,30,31,32}, core={0,3,7,8,10}. The two new features are inserted **immediately after `RU-ARK-SZ`** (stable file order: `RU-ARK` | `RU-ARK-NE` | `RU-ARK-SZ` | `RU-PEO` | `RU-YAM` | `RU-AST` | …).
+  - **Manifests regenerated** with the real scripts and remain deterministic/idempotent (byte-identical re-run): `public/region-keys.json` and `public/region-adjacency.json` are now **1,800 entries each** (was 1,798); adjacency pairs 4,471 → 4,473. The new pairs are `pechora-qwhs ↔ yamal-gosw`, `pechora-qwhs ↔ nenets-qyga`, and `yamal-gosw ↔ severnaya-zemlya-awqp`, while the mainland `arkhangel-sk-lhbk` **loses** its `severnaya-zemlya-awqp` pair (the islets now touch the Yamal band, not the inland core) and keeps its six real neighbours (`karelia-ohem`, `kirov-gfvm`, `komi-eoeh`, `murmansk-etas`, `nenets-qyga`, `vologda-ynvr`). `new-earth-eikt` stays isolated (empty adjacency).
+  - **Fixed-point dataset unchanged except feature count** (1,798 → 1,800): the part/ring/vertex totals (11,794 / 11,795 / 164,801) and the single hole (KZ-KZY) are identical before and after — only the feature grouping changes. The RU-ARK family total stays 78 parts (mainland 5 / NE 42 / SZ 3 / PEO 13 / YAM 15).
+  - **Tests (168, count unchanged — existing cases updated, none added).** `scripts/regions.test.ts` (dataset is now 1,800 features; the Arkhangel feature-pin test now covers all five family members), `scripts/region-keys.test.ts` (1,800 keys; pins the unchanged `arkhangel-sk-lhbk` plus the two new keys), `scripts/region-adjacency.test.ts` (1,800 entries; pins the new PEO/YAM/SZ adjacency and the mainland's loss of the SZ pair), `server/regions.test.ts` (1,800; the RUS country expansion is now **84** sub-regions including all five keys — was 82 after #31). No e2e assertion references the region counts, so the CI e2e suite is unaffected.
+  - **LLM/engine/stub unchanged.** At game creation RUS simply auto-owns the two extra band regions (82 → 84 sub-regions); the LLM's reference table and the player's frontier now include `pechora-qwhs` and `yamal-gosw`.
+  - Deployed to `https://history.dev.kkhost.pl` with the authorized **clean data wipe** (`docker compose down -v` → `up -d --build`; the alpha `history-data` volume was destroyed, resetting all saved games).
+
+## v0.25.0 — 2026-10-14 17:53
+- **#31: the `RU-ARK` mega-region is split into a mainland region plus two island groups** — a pure re-grouping of the existing polygon parts: no new geometry, no coordinate changes. The old single feature (Arkhangel'sk Oblast + the Arctic archipelagos, 78 parts, ~410,187 km²) becomes three features inserted immediately after `RU-ARK` (stable file order: `RU-ARK` | `RU-ARK-NE` | `RU-ARK-SZ` | `RU-AST`):
+  - `RU-ARK` — the mainland (33 parts, ~393,256 km²); it **keeps its existing id and region key `arkhangel-sk-lhbk`**, so existing `Nation.territory` lists and SQLite ownership are untouched (ownership-safe).
+  - `RU-ARK-NE` — New Earth / Franz Josef Land (42 parts, ~15,721 km²) → new region key `new-earth-eikt`. Genuinely isolated (≥100 km from any land), so its adjacency list is **empty**.
+  - `RU-ARK-SZ` — Severnaya Zemlya (3 parts, ~1,210 km²) → new region key `severnaya-zemlya-awqp`. Its islet rings share boundary vertices with the coarsened mainland ring (a contact that pre-existed inside the single pre-split feature — no coordinate change), so it records **one** adjacency pair (SZ ↔ `arkhangel-sk-lhbk`). This deviates from the original "both islands isolated" expectation and is recorded as-is by the manifest's "shares at least one point" definition.
+  - **New pipeline stage** `scripts/split-arkhangel.mjs` (`npm run split:regions`), run between `fill:regions` and `build:region-keys`: deterministic and **idempotent** (a second run is a no-op that writes nothing). It classifies each part by centroid (turf — allowed in `.mjs` only): main = lat < 76 (plus any 76–79.5° band parts west of 55°E — none exist), Severnaya Zemlya = 76 ≤ lat < 79.5 AND lon ≥ 55, New Earth = lat ≥ 79.5. It fails loudly on a mis-split, a missing feature, or a non-MultiPolygon geometry.
+  - **Manifests regenerated** with the real scripts and remain deterministic/idempotent (byte-identical re-run): `public/region-keys.json` and `public/region-adjacency.json` are now **1,798 entries each** (was 1,796); adjacency pairs 4,470 → 4,471 (the one new pair is the SZ ↔ mainland contact; the mainland keeps its 6 real neighbours).
+  - **Fixed-point dataset unchanged except feature count** (1,796 → 1,798): the part/ring/vertex totals (11,794 / 11,795 / 164,801) and the single hole (KZ-KZY) are identical before and after the split.
+  - **Tests (164 → 168).** `scripts/regions.test.ts` (dataset is now 1,798 features; a new test pins the three Arkhangel features and their part counts), `scripts/region-keys.test.ts` (1,798 keys; a new test pins the unchanged main key plus the two new keys), `scripts/region-adjacency.test.ts` (1,798 entries; a new island-adjacency test: New Earth empty, Severnaya Zemlya = [mainland], mainland's neighbour list extended by exactly the SZ pair), `server/regions.test.ts` (1,798; the RUS country expansion is now **82** sub-regions including all three keys — was 80). No e2e assertion references the old counts, so the CI e2e suite is unaffected.
+  - **LLM/engine/stub unchanged.** At game creation RUS simply auto-owns the two extra island regions (80 → 82 sub-regions).
+  - Deployed to `https://history.dev.kkhost.pl` with the authorized **clean data wipe** (`docker compose down -v` → `up -d --build`; the alpha `history-data` volume was destroyed, resetting all saved games).
+
+## v0.24.0 — 2026-10-14 13:41
+- **Part 4b of #16: nation splits and merges — "LLM proposes, player confirms" is now complete.** P4a let the LLM propose a *rename* (a safe, single-field change). Now the same confirm/reject flow actually applies the two destructive ops: a **split** (one nation dissolves into several) and a **merge** (several nations fold into one). This is the last piece of #16 — all three `NationOp` kinds are now applied on player confirm.
+  - **Split (`server/engine.ts`).** `applyNationOp` now handles `kind: "split"`: it resolves the parent `nationRef` and requires **≥2** named parts (fewer → a safe no-op, the op is still resolved and removed). It partitions the parent's **region-key** territory across the parts **in order** — each part gets the keys of its `territory` that the parent actually owns and that no earlier part claimed (the **first part to name a key wins**, so a key is never held twice); any of the parent's keys no part claimed go to **part 0** (in the parent's territory order), so nothing is orphaned. Each new nation gets a **fresh id** (`freshNationId`: first free of `n1`, `n2`, …, tracked in a running `taken` set so ids never collide within the op), the baseline `NEW_NATION_STATS` (a neutral 50/50/50/50 profile — *not* a copy of the parent's, since a small rump state is not the parent's power), a copy of the parent's relations, and the parent's `type`; the parent is then removed and its id dropped from every other nation's relations map (`dropRelationsTo`). If the **parent was the player's nation**, `playerNationId` moves to the chosen part (`edits.playerPart`, clamped into range, default 0) — that same part also receives an `edits.name` override.
+  - **Merge (`server/engine.ts`).** `kind: "merge"`: every input ref and the survivor ref must resolve, at least **two distinct** inputs are required, and the **survivor must be one of the inputs** — any failure is a safe no-op. The survivor keeps its **id** and its **own stats**; it gains the **union of all inputs' territories** (the survivor's keys first, then each other input's unclaimed keys in its own order) and a **union of the inputs' relations** (the survivor's own view of a third party wins, else the first input's); it is renamed to `edits.name` → `into` → its own name (in that precedence). The other inputs are removed and their ids dropped from every remaining nation's relations maps; if the **player led a removed input**, `playerNationId` moves to the survivor.
+  - **Confirm contract extended (`shared/protocol.ts`).** `ConfirmNationOpRequest.edits` is now `{ name?: string; playerPart?: number }` — `name` overrides a rename's target or a merge's merged name; `playerPart` picks which new part the player's nation becomes in a split (default 0). The `SplitOp` / `MergeOp` / `NationOp` doc comments and the `TurnResult.nationOps` doc now describe the *applied* semantics (no longer "a no-op until P4b").
+  - **Prompt (`server/engine.ts`).** The system prompt's JSON contract now shows all three `nationOps` shapes (rename / split / merge), and the HARD CONSTRAINTS gain one line per op explaining when to use it and the "≥2 parts" / "survivor must be an input" rules — so the model knows what it may propose and that each is a player-confirmed PROPOSAL.
+  - **Client (`src/components/NationOpDialog.tsx`).** The dialog now renders all three kinds with a Confirm button (no more "dismiss-only" split/merge rows): a **split** lists each part (name + the number of regions it was assigned) and, when the split's parent is the **player's own nation**, shows a **radio group** to pick which new part the player leads (preselected 0, so the choice is always valid); a **merge** shows the input nations as chips (the **survivor** highlighted) and an **editable name** for the merged state (defaulting to `into`). Rename keeps its editable-name behavior. The new `onConfirm(index, edits?)` signature threads `playerPart` through `ActionPanel` and `App.tsx` (`runConfirmNationOp`) to the API helper.
+  - **Defensive invariants.** All ops are **pure and never throw**: an unresolvable or ambiguous ref, too few parts, or a survivor that isn't an input makes the op a no-op on the world (the proposal is still resolved and removed on confirm, mirroring P4a's ambiguous-ref behavior). **Sole ownership** is preserved by construction (a key lands in at most one new part / one survivor), and `playerNationId` is always re-pointed to a still-existing nation. The **stub is unchanged** — it still never proposes a nation op (`nationOps: []`) — so, like P4a/P4b before it, the new paths are covered by **unit tests only** and the e2e suite (CI, `LLM_STUB=1`) is unaffected.
+- **Tests (`server/engine.test.ts`).** New `freshNationId`, `applyNationOp (split)`, and `applyNationOp (merge)` suites: the partition (first-wins, leftovers-to-part-0, sole ownership, fresh ids/stats/relations, parent removed, relations cleanup, player-pointer move, clamped `playerPart`, `edits.name` on the chosen part), the merge (union territory, survivor stats, relations union with survivor-wins, removed ids dropped from everyone else, into-name, player-pointer move, and the four no-op guards), plus an updated prompt-contract test asserting all three op shapes. The old "split/merge is a no-op" P4a test is retargeted to a 1-part split. The unit suite grows **151 → 164**.
+- **Verification.** Typecheck, lint, **164 unit tests**, and the production build all pass. The e2e suite (CI, `LLM_STUB=1`) carries no nation-op assertions, so it stays green with the unchanged stub.
+- **Deploy:** manual `docker compose up -d --build` on the host (no `down -v`).
+- Part of #16 — major nation changes (P4b, the final part of the epic). #16 was already closed (2026-10-12, after P3 shipped); the PR references it for traceability the same way P4a's PR #38 did ("Part of #16" / "Related: #16") — no auto-close.
+
 ## v0.23.0 — 2026-10-14 12:58
 - **Part 4a of #16: nation renames — "LLM proposes, player confirms."** The LLM can now propose that a nation be renamed during a turn. Unlike stat/relation/territory changes (applied automatically), a rename is stored as a **pending proposal** (`GameState.pendingNationOps`) and only takes effect when the player **confirms** it (optionally editing the new name) or is dropped on **reject**. This is the first of the "major nation changes" the LLM may propose — the `NationOp` contract is stable now; **split** and **merge** are declared in the same union but are *accepted-and-stored, not applied* until P4b.
   - **New `NationOp` union (`shared/protocol.ts`).** `rename` / `split` / `merge`, discriminated by `kind`. Each names its target via a `nationRef` the LLM may give as either a nation **id** or **name**. `TurnResult.nationOps` is a **required** `NationOp[]` (the model's proposals this turn); the confirm/reject request types (`NationOpConfirmRequest` `{index, edits?{name?}}`, `NationOpRejectRequest` `{index}`, response `{game}`) live here too.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "history",
-  "version": "0.23.0",
+  "version": "0.28.0",
   "private": true,
   "type": "module",
   "description": "AI-driven alternate-history simulator — the LLM is the world engine (Pax Historia style).",
@@ -14,8 +14,13 @@
     "cleanup:regions": "node scripts/cleanup-regions.mjs",
     "smooth:regions": "node scripts/smooth-regions.mjs",
     "fill:regions": "node scripts/fill-gaps.mjs",
+    "split:regions": "node scripts/split-arkhangel.mjs",
+    "split:regions:band": "node scripts/split-arkhangel-band.mjs",
     "build:region-keys": "node scripts/build-region-keys.mjs",
     "build:region-adjacency": "node scripts/build-region-adjacency.mjs",
+    "build:region-centroids": "node scripts/build-region-centroids.mjs",
+    "build:region-geo": "node scripts/build-region-geo.mjs",
+    "extract:admin0-pop": "node scripts/extract-admin0-pop.mjs",
     "typecheck": "tsc --noEmit",
     "lint": "eslint .",
     "e2e": "playwright test"

public/ne-admin0-pop.json

@@ -0,0 +1,251 @@
+{
+  "ABW": 106314,
+  "AFG": 38041754,
+  "AGO": 31825295,
+  "AIA": 14731,
+  "ALB": 2854191,
+  "ALD": 29884,
+  "AND": 77142,
+  "ARE": 9770529,
+  "ARG": 44938712,
+  "ARM": 2957731,
+  "ASM": 55312,
+  "ATA": 4490,
+  "ATF": 140,
+  "ATG": 97118,
+  "AUS": 25364307,
+  "AUT": 8877067,
+  "AZE": 10023318,
+  "BDI": 11530580,
+  "BEL": 11484055,
+  "BEN": 11801151,
+  "BFA": 20321378,
+  "BGD": 163046161,
+  "BGR": 6975761,
+  "BHR": 1641172,
+  "BHS": 389482,
+  "BIH": 3301000,
+  "BLM": 9961,
+  "BLR": 9466856,
+  "BLZ": 390353,
+  "BMU": 63918,
+  "BOL": 11513100,
+  "BRA": 211049527,
+  "BRB": 287025,
+  "BRN": 433285,
+  "BTN": 763092,
+  "BWA": 2303697,
+  "CAF": 4745185,
+  "CAN": 37589262,
+  "CHE": 8574832,
+  "CHL": 18952038,
+  "CHN": 1397715000,
+  "CIV": 25716544,
+  "CMR": 25876380,
+  "CNM": 10000,
+  "COD": 86790567,
+  "COG": 5380508,
+  "COK": 17459,
+  "COL": 50339443,
+  "COM": 850886,
+  "CPV": 549935,
+  "CRI": 5047561,
+  "CSI": 4,
+  "CUB": 11333483,
+  "CUW": 157538,
+  "CYM": 64948,
+  "CYN": 326000,
+  "CYP": 1198575,
+  "CZE": 10669709,
+  "DEU": 83132799,
+  "DJI": 973560,
+  "DMA": 71808,
+  "DNK": 5818553,
+  "DOM": 10738958,
+  "DZA": 43053054,
+  "ECU": 17373662,
+  "EGY": 100388073,
+  "ERI": 6081196,
+  "ESB": 7850,
+  "ESP": 47076781,
+  "EST": 1326590,
+  "ETH": 112078730,
+  "FIN": 5520314,
+  "FJI": 889953,
+  "FLK": 3398,
+  "FRA": 67059887,
+  "FRO": 48678,
+  "FSM": 113815,
+  "GAB": 2172579,
+  "GBR": 66834405,
+  "GEO": 3720382,
+  "GGY": 62792,
+  "GHA": 30417856,
+  "GIB": 33701,
+  "GIN": 12771246,
+  "GMB": 2347706,
+  "GNB": 1920922,
+  "GNQ": 1355986,
+  "GRC": 10716322,
+  "GRD": 112003,
+  "GRL": 56225,
+  "GTM": 16604026,
+  "GUM": 167294,
+  "GUY": 782766,
+  "HKG": 7507400,
+  "HND": 9746117,
+  "HRV": 4067500,
+  "HTI": 11263077,
+  "HUN": 9769949,
+  "IDN": 270625568,
+  "IMN": 84584,
+  "IND": 1366417754,
+  "IOA": 2387,
+  "IOT": 3000,
+  "IRL": 4941444,
+  "IRN": 82913906,
+  "IRQ": 39309783,
+  "ISL": 361313,
+  "ISR": 9053300,
+  "ITA": 60297396,
+  "JAM": 2948279,
+  "JEY": 107800,
+  "JOR": 10101694,
+  "JPN": 126264931,
+  "KAB": 36175,
+  "KAS": 6000,
+  "KAZ": 18513930,
+  "KEN": 52573973,
+  "KGZ": 6456900,
+  "KHM": 16486542,
+  "KIR": 117606,
+  "KNA": 52834,
+  "KOR": 51709098,
+  "KOS": 1794248,
+  "KWT": 4207083,
+  "LAO": 7169455,
+  "LBN": 6855713,
+  "LBR": 4937374,
+  "LBY": 6777452,
+  "LCA": 182790,
+  "LIE": 38019,
+  "LKA": 21803000,
+  "LSO": 2125268,
+  "LTU": 2786844,
+  "LUX": 619896,
+  "LVA": 1912789,
+  "MAC": 640445,
+  "MAF": 38002,
+  "MAR": 36471769,
+  "MCO": 38964,
+  "MDA": 2657637,
+  "MDG": 26969307,
+  "MDV": 530953,
+  "MEX": 127575529,
+  "MHL": 58791,
+  "MKD": 2083459,
+  "MLI": 19658031,
+  "MLT": 502653,
+  "MMR": 54045420,
+  "MNE": 622137,
+  "MNG": 3225167,
+  "MNP": 57216,
+  "MOZ": 30366036,
+  "MRT": 4525696,
+  "MSR": 4649,
+  "MUS": 1265711,
+  "MWI": 18628747,
+  "MYS": 31949777,
+  "NAM": 2494530,
+  "NCL": 287800,
+  "NER": 23310715,
+  "NFK": 2169,
+  "NGA": 200963599,
+  "NIC": 6545502,
+  "NIU": 1620,
+  "NLD": 17332850,
+  "NOR": 5347896,
+  "NPL": 28608710,
+  "NRU": 12581,
+  "NZL": 4917000,
+  "OMN": 4974986,
+  "PAK": 216565318,
+  "PAN": 4246439,
+  "PCN": 54,
+  "PER": 32510453,
+  "PGA": 100,
+  "PHL": 108116615,
+  "PLW": 18008,
+  "PNG": 8776109,
+  "POL": 37970874,
+  "PRI": 3193694,
+  "PRK": 25666161,
+  "PRT": 10269417,
+  "PRY": 7044636,
+  "PSX": 4685306,
+  "PYF": 279287,
+  "QAT": 2832067,
+  "ROU": 19356544,
+  "RUS": 144373535,
+  "RWA": 12626950,
+  "SAH": 603253,
+  "SAU": 34268528,
+  "SDN": 42813238,
+  "SDS": 11062113,
+  "SEN": 16296364,
+  "SGP": 5703569,
+  "SGS": 30,
+  "SHN": 4534,
+  "SLB": 669823,
+  "SLE": 7813215,
+  "SLV": 6453553,
+  "SMR": 33860,
+  "SOL": 5096159,
+  "SOM": 10192317,
+  "SPM": 5997,
+  "SRB": 6944975,
+  "STP": 215056,
+  "SUR": 581363,
+  "SVK": 5454073,
+  "SVN": 2087946,
+  "SWE": 10285453,
+  "SWZ": 1148130,
+  "SXM": 40733,
+  "SYC": 97625,
+  "SYR": 17070135,
+  "TCA": 38191,
+  "TCD": 15946876,
+  "TGO": 8082366,
+  "THA": 69625582,
+  "TJK": 9321018,
+  "TKM": 5942089,
+  "TLS": 1293119,
+  "TON": 104494,
+  "TTO": 1394973,
+  "TUN": 11694719,
+  "TUR": 83429615,
+  "TUV": 11646,
+  "TWN": 23568378,
+  "TZA": 58005463,
+  "UGA": 44269594,
+  "UKR": 44385155,
+  "UMI": 300,
+  "URY": 3461734,
+  "USA": 328239523,
+  "USG": 6000,
+  "UZB": 33580650,
+  "VAT": 825,
+  "VCT": 110589,
+  "VEN": 28515829,
+  "VGB": 30030,
+  "VIR": 106631,
+  "VNM": 96462106,
+  "VUT": 299882,
+  "WLF": 11558,
+  "WSB": 7850,
+  "WSM": 197097,
+  "YEM": 29161922,
+  "ZAF": 58558270,
+  "ZMB": 17861030,
+  "ZWE": 14645468
+}

public/region-adjacency.json

@@ -7587,6 +7587,7 @@
   "nenets-qyga": [
     "arkhangel-sk-lhbk",
     "komi-eoeh",
+    "pechora-qwhs",
     "yamal-nenets-aqsx"
   ],
   "neuquen-yvne": [
@@ -7614,6 +7615,7 @@
     "ontario-bzqu",
     "quebec-yegk"
   ],
+  "new-earth-eikt": [],
   "new-hampshire-koki": [
     "maine-maiz",
     "massachusetts-ggid",
@@ -8748,6 +8750,10 @@
     "soriano-ixbv",
     "tacuarembo-yekg"
   ],
+  "pechora-qwhs": [
+    "nenets-qyga",
+    "yamal-gosw"
+  ],
   "peloponnisos-wqyw": [
     "dytiki-ellada-mlyj",
     "sterea-ellada-inyu"
@@ -10010,6 +10016,9 @@
     "medea-elbf",
     "skikda-odba"
   ],
+  "severnaya-zemlya-awqp": [
+    "yamal-gosw"
+  ],
   "sevilla-oxma": [
     "badajoz-ciwt",
     "cadiz-aazc",
@@ -12160,6 +12169,10 @@
     "iwate-uvfz",
     "niigata-idhx"
   ],
+  "yamal-gosw": [
+    "pechora-qwhs",
+    "severnaya-zemlya-awqp"
+  ],
   "yamal-nenets-aqsx": [
     "khanty-mansiy-tkto",
     "komi-eoeh",

public/region-keys.json

@@ -1305,6 +1305,10 @@
   "RU-ALT": "altay-mfuq",
   "RU-AMU": "amur-clbp",
   "RU-ARK": "arkhangel-sk-lhbk",
+  "RU-ARK-NE": "new-earth-eikt",
+  "RU-ARK-SZ": "severnaya-zemlya-awqp",
+  "RU-PEO": "pechora-qwhs",
+  "RU-YAM": "yamal-gosw",
   "RU-AST": "astrakhan-anec",
   "RU-BA": "bashkortostan-uovk",
   "RU-BEL": "belgorod-wxjk",

scripts/build-region-centroids.mjs

@@ -0,0 +1,132 @@
+/**
+ * scripts/build-region-centroids.mjs — build the precomputed region-centroid
+ * manifest: `public/region-centroids.json` = `{ "<regionKey>": { "lat": <number>, "lon": <number>, "spread": <number> }, ... }`.
+ *
+ * For every sub-region (region key, see `public/region-keys.json`) this records
+ * the point the LLM's map markers (v0.27, #44) will be anchored to: the
+ * **centroid of the region's largest-area part** (a MultiPolygon's biggest
+ * island/lake-piece rather than an area-weighted average of all parts), plus
+ * a `spread` value ≈ 0.1 × the smallest bbox dimension of that part (in
+ * degrees) — the engine scatters markers of one region within ±(spread/2)
+ * around the centroid using a deterministic per-marker offset, so several
+ * markers of the same region do not stack on one pixel.
+ *
+ * Method — plain turf on the pre-generated geo file (turf is allowed in .mjs
+ * scripts; it is deliberately kept OUT of the TS typecheck program, see the
+ * v0.17 note). For each feature we (1) split a MultiPolygon into its parts
+ * (a plain Polygon is its own single part), (2) pick the part with the
+ * greatest `@turf/area`, (3) take `@turf/centroid` of that part and
+ * `@turf/bbox` of that part, and (4) round everything to 6 decimal places
+ * (≈ 0.1 m at this scale — far below the map's visual precision).
+ *
+ * Output contract (asserted by scripts/region-centroids.test.ts):
+ *   - one entry for **every** region key, keyed identically to
+ *     `public/region-keys.json` (same key set, 1,800 entries);
+ *   - each centroid lies inside its region's (largest part's) bbox;
+ *   - `spread` is a non-negative number of degrees (0 for degenerate parts);
+ *   - values are rounded to at most 6 decimal places.
+ *
+ * Deterministic + idempotent: the input files are fixed, turf is a pure
+ * geometric computation, the output keeps the geo file's (stable) feature
+ * order and rounds to fixed precision — so a re-run rewrites a byte-identical
+ * file (the test re-runs this script and compares bytes).
+ *
+ * Usage: `node scripts/build-region-centroids.mjs`  (or `npm run build:region-centroids`).
+ */
+import { readFileSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import area from '@turf/area';
+import bbox from '@turf/bbox';
+import centroid from '@turf/centroid';
+import { feature } from '@turf/helpers';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+
+const round6 = (v) => Math.round(v * 1e6) / 1e6;
+
+// --- load the geo + region-key manifest (plain parse; keys join feature->key) --
+const geo = JSON.parse(readFileSync(path.join(root, 'public', 'regions.geo.json'), 'utf8'));
+const idToKey = JSON.parse(readFileSync(path.join(root, 'public', 'region-keys.json'), 'utf8'));
+
+/**
+ * The polygon parts of a geometry: a MultiPolygon's individual polygons, a
+ * plain Polygon as its own single part, anything else as an empty list (the
+ * caller falls back to the whole-feature centroid).
+ */
+function partsOf(geometry) {
+  if (geometry?.type === 'MultiPolygon') return geometry.coordinates ?? [];
+  if (geometry?.type === 'Polygon') return [geometry.coordinates];
+  return [];
+}
+
+const manifest = {};
+let skipped = 0;
+for (const f of geo.features ?? []) {
+  const id = f.id == null ? '' : String(f.id);
+  const key = idToKey[id];
+  if (!key) continue; // a geo feature with no manifest entry is skipped
+  const parts = partsOf(f.geometry);
+  if (parts.length === 0) {
+    // Degenerate geometry (a point/line region): anchor at the feature's own
+    // centroid. Can't happen with the current 1,800-polygon dataset, but the
+    // fallback keeps the manifest complete if the generator ever changes.
+    skipped += 1;
+    const c = centroid(feature(f.geometry));
+    const b = bbox(feature(f.geometry));
+    manifest[key] = {
+      lat: round6(c.geometry.coordinates[1]),
+      lon: round6(c.geometry.coordinates[0]),
+      spread: round6(Math.min(b[2] - b[0], b[3] - b[1]) * 0.1),
+    };
+    continue;
+  }
+  // Pick the part with the greatest area (km²) and anchor to IT, so a
+  // multi-part region's markers cluster on its main mass, not between parts.
+  let best = 0;
+  let bestArea = -1;
+  for (let i = 0; i < parts.length; i++) {
+    const a = area(feature({ type: 'Polygon', coordinates: parts[i] }));
+    if (a > bestArea) {
+      bestArea = a;
+      best = i;
+    }
+  }
+  const part = feature({ type: 'Polygon', coordinates: parts[best] });
+  const c = centroid(part);
+  const b = bbox(part);
+  manifest[key] = {
+    lat: round6(c.geometry.coordinates[1]),
+    lon: round6(c.geometry.coordinates[0]),
+    spread: round6(Math.min(b[2] - b[0], b[3] - b[1]) * 0.1),
+  };
+}
+
+// --- hard assertions (the test re-checks these against the committed file) ---
+const expectedKeys = Object.values(idToKey);
+if (Object.keys(manifest).length !== expectedKeys.length) {
+  throw new Error(
+    `expected ${expectedKeys.length} centroid entries (one per region key), got ${Object.keys(manifest).length}`,
+  );
+}
+for (const k of expectedKeys) {
+  if (!(k in manifest)) throw new Error(`missing centroid for region key ${JSON.stringify(k)}`);
+}
+for (const [k, v] of Object.entries(manifest)) {
+  if (!Number.isFinite(v.lat) || !Number.isFinite(v.lon) || !Number.isFinite(v.spread)) {
+    throw new Error(`non-finite centroid for ${k}: ${JSON.stringify(v)}`);
+  }
+  if (v.spread < 0) throw new Error(`negative spread for ${k}: ${v.spread}`);
+}
+
+// --- write idempotently (stable order = insertion order = geo file order) ---
+writeFileSync(path.join(root, 'public', 'region-centroids.json'), JSON.stringify(manifest, null, 2) + '\n');
+
+// --- summary ------------------------------------------------------------------
+const spreads = Object.values(manifest).map((v) => v.spread);
+console.log(
+  `[build-region-centroids] wrote public/region-centroids.json — ${Object.keys(manifest).length} region keys` +
+    (skipped ? ` (${skipped} non-polygon fallbacks)` : '') +
+    `, spread min/max ${Math.min(...spreads)} / ${Math.max(...spreads)} deg`,
+);

scripts/build-region-geo.mjs

@@ -0,0 +1,165 @@
+/**
+ * scripts/build-region-geo.mjs — build the region **geo** manifest:
+ * `public/region-geo.json` = `{ "<regionKey>": { "area": <number>, "population": <number> }, ... }`.
+ *
+ * For every sub-region (region key, see `public/region-keys.json`) this records
+ * two facts the v0.28 per-region stats model (and its area×population weighting)
+ * needs:
+ *   - `area`       — the region's **total** surface area in km², from
+ *                    `@turf/area` on the FINAL generated feature
+ *                    (`public/regions.geo.json`) — turf reports square metres,
+ *                    so the raw value is divided by 1e6 — rounded to 2 decimals.
+ *   - `population` — the region's share of its **parent country's** real
+ *                    population (Natural Earth 1:10m admin-0 `POP_EST`, from the
+ *                    committed `public/ne-admin0-pop.json`), distributed across
+ *                    the country's sub-regions **proportional to each region's
+ *                    area** (a first-order "uniform population density within a
+ *                    country" approximation — Natural Earth admin-1, which the
+ *                    region generator uses, carries no per-unit population).
+ *
+ * Population distribution uses **largest remainder** per country, so the sum of
+ * a country's sub-region populations is EXACTLY the country's POP_EST, and the
+ * sum over all 1,800 regions is EXACTLY the sum of the 177 repo countries'
+ * POP_EST (7,654,092,021) — no rounding drift.
+ *
+ * Method — plain turf on the pre-generated geo file (turf is allowed in .mjs
+ * scripts; it is deliberately kept OUT of the TS typecheck program, see the
+ * v0.17 note). The population source is the COMMITTED `public/ne-admin0-pop.json`
+ * (a small derived table produced once by `scripts/extract-admin0-pop.mjs` from
+ * the 13 MB Natural Earth admin-0 file, which we do NOT commit) — so this build
+ * is fully reproducible in CI.
+ *
+ * Output contract (asserted by scripts/region-geo.test.ts):
+ *   - one entry for **every** region key, keyed identically to
+ *     `public/region-keys.json` (same key set, 1,800 entries);
+ *   - `area` is a finite number >= 0 (km², <= 2 decimals);
+ *   - `population` is a non-negative integer;
+ *   - the total population across all entries is a non-negative integer.
+ *
+ * Deterministic + idempotent: fixed inputs (the geo file, the key manifest, and
+ * the committed population table), pure turf, largest-remainder with a
+ * (remainder desc, key asc) tie-break, and stable sorted key order → a re-run
+ * rewrites a byte-identical file (the test re-runs this script and compares
+ * bytes).
+ *
+ * Usage: `node scripts/build-region-geo.mjs`  (or `npm run build:region-geo`).
+ */
+import { readFileSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import area from '@turf/area';
+import { feature } from '@turf/helpers';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+
+const round2 = (v) => Math.round(v * 100) / 100;
+
+// --- load the inputs (plain parse) ------------------------------------------
+const geoPath = path.join(root, 'public', 'regions.geo.json');
+const keysPath = path.join(root, 'public', 'region-keys.json');
+const popPath = path.join(root, 'public', 'ne-admin0-pop.json');
+
+let geo, idToKey, popByCountry;
+try {
+  geo = JSON.parse(readFileSync(geoPath, 'utf8'));
+  idToKey = JSON.parse(readFileSync(keysPath, 'utf8'));
+  popByCountry = JSON.parse(readFileSync(popPath, 'utf8'));
+} catch (err) {
+  console.error(
+    `[build-region-geo] could not load the inputs (${geoPath}, ${keysPath}, ${popPath}). ` +
+      `Is public/ne-admin0-pop.json present? Regenerate it with scripts/extract-admin0-pop.mjs.`,
+  );
+  throw err;
+}
+
+/**
+ * One pass over the geo features: for each region key record its (unrounded)
+ * turf area and its parent ISO_A3, then group the keys by parent so the
+ * population can be distributed per country.
+ */
+const regionArea = new Map(); // key -> unrounded area (km²)
+const regionParent = new Map(); // key -> parent ISO_A3
+for (const f of geo.features ?? []) {
+  const id = f.id == null ? '' : String(f.id);
+  const key = idToKey[id];
+  if (!key) continue; // a geo feature with no manifest entry is skipped
+  // @turf/area reports square METRES; the manifest stores km².
+  const a = area(feature(f.geometry)) / 1e6;
+  regionArea.set(key, a);
+  regionParent.set(key, typeof f.properties?.parent === 'string' ? f.properties.parent : '');
+}
+
+// Group region keys by parent country (file order is stable, but we sort for
+// deterministic population distribution).
+const keysByCountry = new Map(); // parent -> string[] of keys
+for (const [key, parent] of regionParent) {
+  if (!parent) continue; // a region with no parent has no population source
+  const list = keysByCountry.get(parent);
+  if (list) list.push(key);
+  else keysByCountry.set(parent, [key]);
+}
+
+const population = new Map(); // key -> integer population
+for (const [parent, keys] of keysByCountry) {
+  keys.sort(); // deterministic ordering for the tie-break
+  const P = Number.isFinite(popByCountry[parent]) ? Math.max(0, popByCountry[parent]) : 0;
+  const totalArea = keys.reduce((s, k) => s + (regionArea.get(k) || 0), 0);
+  if (P <= 0 || totalArea <= 0) {
+    for (const k of keys) population.set(k, 0);
+    continue;
+  }
+  // Largest remainder: floor each share, then hand out the leftover 1s to the
+  // regions with the largest fractional remainders (ties broken by key asc).
+  const shares = keys.map((k) => {
+    const a = regionArea.get(k) || 0;
+    const ideal = (P * a) / totalArea;
+    return { k, floor: Math.floor(ideal), rem: ideal - Math.floor(ideal) };
+  });
+  const distributed = shares.reduce((s, x) => s + x.floor, 0);
+  let deficit = P - distributed; // 0 <= deficit < keys.length
+  const order = shares
+    .map((x, i) => ({ i, rem: x.rem, k: x.k }))
+    .sort((a, b) => (b.rem - a.rem) || (a.k < b.k ? -1 : a.k > b.k ? 1 : 0));
+  for (let i = 0; i < order.length && deficit > 0; i++) {
+    shares[order[i].i].floor += 1;
+    deficit -= 1;
+  }
+  for (const x of shares) population.set(x.k, x.floor);
+}
+
+// --- assemble the manifest (sorted keys) -------------------------------------
+const expectedKeys = Object.values(idToKey);
+const manifest = {};
+for (const k of [...expectedKeys].sort()) {
+  const a = regionArea.get(k);
+  const p = population.get(k);
+  if (a === undefined || p === undefined) {
+    throw new Error(`region key ${JSON.stringify(k)} has no computed area/population`);
+  }
+  manifest[k] = { area: round2(a), population: p };
+}
+
+// --- hard assertions (the test re-checks these against the committed file) ----
+if (Object.keys(manifest).length !== expectedKeys.length) {
+  throw new Error(
+    `expected ${expectedKeys.length} region-geo entries (one per region key), got ${Object.keys(manifest).length}`,
+  );
+}
+let totalPop = 0;
+let zeros = 0;
+for (const [k, v] of Object.entries(manifest)) {
+  if (!Number.isFinite(v.area) || v.area < 0) throw new Error(`bad area for ${k}: ${JSON.stringify(v)}`);
+  if (!Number.isInteger(v.population) || v.population < 0) throw new Error(`bad population for ${k}: ${JSON.stringify(v)}`);
+  if (v.area === 0) zeros += 1;
+  totalPop += v.population;
+}
+
+// --- write idempotently (sorted keys, 2-space indent, trailing newline) ------
+writeFileSync(path.join(root, 'public', 'region-geo.json'), JSON.stringify(manifest, null, 2) + '\n');
+
+// --- summary ------------------------------------------------------------------
+console.log(
+  `[build-region-geo] wrote public/region-geo.json — ${Object.keys(manifest).length} region keys` +
+    `${zeros ? ` (${zeros} zero-area regions)` : ''}, total population ${totalPop.toLocaleString('en-US')}`,
+);

scripts/build-region-keys.mjs

@@ -21,7 +21,7 @@
  *     SQLite and shown to the LLM. Within any name-slug group (e.g. the six
  *     regions all named "Western") the 4-char codes are made distinct by
  *     re-deriving with a deterministic salt on collision, which guarantees the
- *     full key is unique across all 1,796 regions.
+ *     full key is unique across all 1,800 regions.
  *
  * Output: `public/region-keys.json` — a `{ [stableFeatureId]: regionKey }`
  * object, e.g. `{ "FR-57": "brittany-xk2a" }`, in file (stable) order. The map
@@ -107,8 +107,8 @@ const geoFile = path.join(root, 'public', 'regions.geo.json');
 const geo = JSON.parse(readFileSync(geoFile, 'utf8'));
 const features = Array.isArray(geo?.features) ? geo.features : [];
 
-if (features.length !== 1796) {
-  throw new Error(`expected 1,796 regions, got ${features.length} — regions.geo.json changed; re-verify the region-key contract`);
+if (features.length !== 1800) {
+  throw new Error(`expected 1,800 regions, got ${features.length} — regions.geo.json changed; re-verify the region-key contract`);
 }
 
 // Group features by their (computed) name-slug, preserving file order, so the
@@ -154,5 +154,5 @@ writeFileSync(path.join(root, 'public', 'region-keys.json'), out);
 const western = Object.entries(manifest)
   .filter(([, k]) => k.startsWith('western-'))
   .sort((a, b) => a[0] < b[0] ? -1 : 1);
-console.log(`[build-region-keys] wrote public/region-keys.json — ${keys.length} unique region keys (1,796 expected)`);
+console.log(`[build-region-keys] wrote public/region-keys.json — ${keys.length} unique region keys (1,800 expected)`);
 console.log(`  western group: ${western.map(([id, k]) => `${id}=${k}`).join(', ')}`);

scripts/extract-admin0-pop.mjs

@@ -0,0 +1,78 @@
+/**
+ * scripts/extract-admin0-pop.mjs — one-time extraction of the population
+ * SOURCE for the region-geo manifest: `public/ne-admin0-pop.json`.
+ *
+ * Output = `{ "<ADM0_A3>": <POP_EST>, ... }` — the estimated population
+ * (POP_EST) of every Natural Earth 1:10m **admin-0 country** code, keeping
+ * the **maximum** POP_EST seen for each code (Natural Earth ships a few
+ * duplicated / broken-out features per code, e.g. the `TLC` stubs, whose
+ * POP_EST is 0; the real country always wins by having the larger value).
+ * Only codes with a finite, positive POP_EST are recorded (a 0/null POP_EST
+ * has nothing to distribute). Keys are sorted; the file is written with
+ * 2-space indent + trailing newline (deterministic, committed).
+ *
+ * Why a separate committed file: `public/region-geo.json` (built by
+ * `build-region-geo.mjs`) needs a per-country population, but the raw
+ * Natural Earth GeoJSON (13 MB) is a *source* file we deliberately do NOT
+ * commit (see the AGENTS.md data-pipeline note). This script distils it
+ * into a tiny (a few KB) derived table that IS committed, so the region-geo
+ * builder stays fully reproducible in CI without the source present.
+ * Re-run only when the underlying Natural Earth data changes.
+ *
+ * The 1:10m admin-1 file (the one the region generator uses) carries NO
+ * population; the 1:10m admin-0 file does (uppercase `POP_EST` / `ADM0_A3`).
+ *
+ * Usage:
+ *   NE_ADMIN0=/path/to/ne_10m_admin_0_countries.geojson node scripts/extract-admin0-pop.mjs
+ * (default source: /tmp/ne10m_admin0.geojson)
+ */
+import { readFileSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+
+const src = process.env.NE_ADMIN0 || '/tmp/ne10m_admin0.geojson';
+let raw;
+try {
+  raw = readFileSync(src, 'utf8');
+} catch (err) {
+  console.error(
+    `[extract-admin0-pop] could not read the Natural Earth admin-0 source at ${src}. ` +
+      `Download it (ne_10m_admin_0_countries.geojson) and re-run with NE_ADMIN0 pointing at it.`,
+  );
+  throw err;
+}
+
+const geo = JSON.parse(raw);
+
+/** ADM0_A3 -> max finite, positive POP_EST. */
+const byCode = new Map();
+for (const f of geo.features ?? []) {
+  const p = f.properties ?? {};
+  const code = typeof p.ADM0_A3 === 'string' ? p.ADM0_A3 : '';
+  const pop = typeof p.POP_EST === 'number' ? p.POP_EST : NaN;
+  if (!code || !Number.isFinite(pop) || pop <= 0) continue;
+  const prev = byCode.get(code);
+  if (prev === undefined || pop > prev) byCode.set(code, Math.round(pop));
+}
+
+if (byCode.size === 0) {
+  throw new Error('[extract-admin0-pop] no finite positive POP_EST found in the source — wrong file?');
+}
+
+// Deterministic: sorted keys, 2-space indent, trailing newline.
+const keys = [...byCode.keys()].sort();
+const manifest = {};
+for (const k of keys) manifest[k] = byCode.get(k);
+
+const out = path.join(root, 'public', 'ne-admin0-pop.json');
+writeFileSync(out, JSON.stringify(manifest, null, 2) + '\n');
+
+let sum = 0;
+for (const v of byCode.values()) sum += v;
+console.log(
+  `[extract-admin0-pop] wrote public/ne-admin0-pop.json — ${byCode.size} country codes, ` +
+    `total population ${sum.toLocaleString('en-US')} (Natural Earth 1:10m admin-0, max POP_EST per code)`,
+);

scripts/region-adjacency.test.ts

@@ -34,7 +34,7 @@ describe('region-adjacency.json', () => {
     const adjacencyKeys = new Set(Object.keys(adjacency));
     expect(adjacencyKeys).toEqual(manifestKeys);
     expect(Object.keys(adjacency)).toHaveLength(keys.size);
-    expect(adjacencyKeys.size).toBe(1796);
+    expect(adjacencyKeys.size).toBe(1800);
   });
 
   it('every neighbour is itself a valid region key (referential integrity)', () => {
@@ -84,4 +84,32 @@ describe('region-adjacency.json', () => {
     expect(adjacency['moselle-rygy']?.includes('baden-wurttemberg-oyje')).toBe(true);
     expect(adjacency['baden-wurttemberg-oyje']?.includes('moselle-rygy')).toBe(true);
   });
+
+  it("the #31 + #41 Arctic splits: New Earth isolated; Severnaya Zemlya, Pechora and Yamal adjacency", () => {
+    // v0.25 (#31) split RU-ARK into the mainland (arkhangel-sk-lhbk), the
+    // Franz Josef Land islets (new-earth-eikt) and the Severnaya Zemlya
+    // islets (severnaya-zemlya-awqp). New Earth sits ~100+ km from any land
+    // → a genuinely isolated island (empty list).
+    // v0.26 (#41) repartitioned the mainland: the 5 lat < 68 parts stay
+    // arkhangel-sk-lhbk, and the 28 lat ≥ 68 band parts became pechora-qwhs
+    // (the SW cell) and yamal-gosw (the NE cell). The Severnaya Zemlya
+    // islets' digitized rings touch the NE band part (now yamal-gosw), not
+    // the trimmed core, so SZ now borders Yamal (its former mainland contact
+    // moved to Yamal). The trimmed core keeps its real mainland neighbours
+    // but loses the SZ contact. Pechora (SW) borders the existing Nenets
+    // region to the south and Yamal to the north.
+    expect(adjacency['new-earth-eikt']).toEqual([]);
+    expect(adjacency['severnaya-zemlya-awqp']).toEqual(['yamal-gosw']);
+    expect(adjacency['pechora-qwhs']).toEqual(['nenets-qyga', 'yamal-gosw']);
+    expect(adjacency['yamal-gosw']).toEqual(['pechora-qwhs', 'severnaya-zemlya-awqp']);
+    // the trimmed core keeps its real neighbours (the band's SZ contact moved to Yamal)
+    expect(adjacency['arkhangel-sk-lhbk']).toEqual([
+      'karelia-ohem',
+      'kirov-gfvm',
+      'komi-eoeh',
+      'murmansk-etas',
+      'nenets-qyga',
+      'vologda-ynvr',
+    ]);
+  });
 });

scripts/region-centroids.test.ts

@@ -0,0 +1,158 @@
+/**
+ * scripts/region-centroids.test.ts — validation for the committed
+ * `public/region-centroids.json` (built by `scripts/build-region-centroids.mjs`).
+ *
+ * The manifest maps each region key to the anchor point a map marker (v0.27,
+ * #44) is placed at: the centroid of the region's largest-area part, plus a
+ * `spread` (≈ 0.1 × that part's smallest bbox dimension, in degrees) that the
+ * engine uses to scatter multiple markers of one region around the centroid.
+ * It is a load-bearing data artifact for the marker placement path — this test
+ * pins its contract.
+ *
+ * Deliberately dependency-free: it reads the JSON with plain `fs`/`JSON.parse`
+ * and computes bbox checks by iterating coordinates directly (no `@turf`/
+ * geojson types, which would pull `@types/geojson` into the tsc program and
+ * break `WorldMap.tsx` — see the v0.17 note). Mirrors the style of
+ * `scripts/region-adjacency.test.ts`; the determinism test re-runs the (turf
+ * `.mjs`) builder and compares bytes, matching that the builder is idempotent.
+ */
+import { readFileSync } from 'node:fs';
+import { execFileSync } from 'node:child_process';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+
+function readJson(rel: string): Record<string, unknown> {
+  return JSON.parse(readFileSync(path.join(root, rel), 'utf8'));
+}
+
+interface CentroidEntry {
+  lat: number;
+  lon: number;
+  spread: number;
+}
+
+/** All [lon, lat] coordinate pairs of a Polygon / MultiPolygon geometry. */
+function allCoords(geometry: { type?: string; coordinates?: unknown }): Array<[number, number]> {
+  const c = geometry?.coordinates as
+    | Array<Array<[number, number]>>
+    | Array<Array<Array<[number, number]>>>
+    | undefined;
+  if (!c) return [];
+  if (geometry?.type === 'Polygon') {
+    const rings = c as Array<Array<[number, number]>>;
+    const out: Array<[number, number]> = [];
+    for (const ring of rings) for (const p of ring) out.push(p);
+    return out;
+  }
+  if (geometry?.type === 'MultiPolygon') {
+    const polys = c as Array<Array<Array<[number, number]>>>;
+    const out: Array<[number, number]> = [];
+    for (const poly of polys) for (const ring of poly) for (const p of ring) out.push(p);
+    return out;
+  }
+  return [];
+}
+
+/** The bounding box [minLon, minLat, maxLon, maxLat] of a geometry. */
+function bboxOf(geometry: { type?: string; coordinates?: unknown }): [number, number, number, number] {
+  let minLon = Infinity;
+  let minLat = Infinity;
+  let maxLon = -Infinity;
+  let maxLat = -Infinity;
+  for (const [x, y] of allCoords(geometry)) {
+    if (x < minLon) minLon = x;
+    if (y < minLat) minLat = y;
+    if (x > maxLon) maxLon = x;
+    if (y > maxLat) maxLat = y;
+  }
+  return [minLon, minLat, maxLon, maxLat];
+}
+
+describe('region-centroids.json', () => {
+  const centroids = readJson('public/region-centroids.json') as Record<string, CentroidEntry>;
+  const manifest = readJson('public/region-keys.json') as Record<string, string>;
+  const geo = readJson('public/regions.geo.json') as {
+    features?: Array<{ id?: string | number; geometry?: { type?: string; coordinates?: unknown } }>;
+  };
+  const keys = Object.values(manifest);
+
+  // featureId -> feature, then regionKey -> feature (via the key manifest).
+  const featureByKey = new Map<string, { geometry?: { type?: string; coordinates?: unknown } }>();
+  for (const f of geo.features ?? []) {
+    const key = manifest[String(f.id)];
+    if (key) featureByKey.set(key, f);
+  }
+
+  it('has exactly one entry per region key (same key set as region-keys.json)', () => {
+    expect(new Set(Object.keys(centroids))).toEqual(new Set(keys));
+    expect(Object.keys(centroids)).toHaveLength(1800);
+  });
+
+  it('every entry is a finite { lat, lon, spread } with a non-negative spread, in world bounds', () => {
+    for (const [k, v] of Object.entries(centroids)) {
+      expect(Number.isFinite(v.lat), `non-finite lat for ${k}`).toBe(true);
+      expect(Number.isFinite(v.lon), `non-finite lon for ${k}`).toBe(true);
+      expect(Number.isFinite(v.spread), `non-finite spread for ${k}`).toBe(true);
+      expect(v.spread >= 0, `negative spread for ${k}`).toBe(true);
+      expect(v.lat >= -90 && v.lat <= 90, `lat out of range for ${k}: ${v.lat}`).toBe(true);
+      expect(v.lon >= -180 && v.lon <= 180, `lon out of range for ${k}: ${v.lon}`).toBe(true);
+    }
+  });
+
+  it('each centroid lies inside its region feature bounding box', () => {
+    // The recorded point is the centroid of the LARGEST part, which is a subset
+    // of the whole feature, so it must fall inside the feature's overall bbox.
+    let checked = 0;
+    for (const [key, c] of Object.entries(centroids)) {
+      const feat = featureByKey.get(key);
+      if (!feat?.geometry) continue;
+      const [minLon, minLat, maxLon, maxLat] = bboxOf(feat.geometry);
+      const eps = 1e-4; // allow for the 6-dp rounding in the builder
+      expect(
+        c.lat >= minLat - eps && c.lat <= maxLat + eps,
+        `lat ${c.lat} outside bbox [${minLat}, ${maxLat}] for ${key}`,
+      ).toBe(true);
+      expect(
+        c.lon >= minLon - eps && c.lon <= maxLon + eps,
+        `lon ${c.lon} outside bbox [${minLon}, ${maxLon}] for ${key}`,
+      ).toBe(true);
+      checked++;
+    }
+    expect(checked).toBe(1800);
+  });
+
+  it('spot-checks a couple of well-known anchors land in the right place', () => {
+    // Region keys are sub-national (states/provinces), so we spot-check a few
+    // whose geography is unambiguous. A gross error in the centroid method
+    // (e.g. averaging across all parts of a large multi-part region, or a
+    // lon/lat swap) would land one of these far off.
+    const near = (k: string, lat: number, lon: number, tol: number) => {
+      const c = centroids[k];
+      expect(c, `missing centroid for ${k}`).toBeDefined();
+      expect(Math.abs(c!.lat - lat)).toBeLessThan(tol);
+      expect(Math.abs(c!.lon - lon)).toBeLessThan(tol);
+    };
+    near('ain-lqtt', 46.16, 4.8, 0.5); // FR-01 — eastern France
+    near('california-kikh', 36.87, -120.67, 0.7); // US-CA — central California
+    near('alberta-zopq', 52.09, -116.94, 1.5); // CA-AB — Alberta (large province)
+    near('acre-ekzw', -9.49, -71.11, 0.5); // BR-AC — western Brazil
+  });
+
+  it('is deterministic: re-running the builder rewrites a byte-identical file', () => {
+    const file = path.join(root, 'public', 'region-centroids.json');
+    const before = readFileSync(file, 'utf8');
+    // The builder is cwd-independent (it resolves the repo root from its own
+    // location) and idempotent: same input files + pure turf + fixed rounding
+    // + stable insertion order → identical bytes.
+    execFileSync(process.execPath, [path.join(root, 'scripts', 'build-region-centroids.mjs')], {
+      cwd: root,
+      stdio: 'pipe',
+    });
+    const after = readFileSync(file, 'utf8');
+    expect(after).toBe(before);
+  });
+});

scripts/region-geo.test.ts

@@ -0,0 +1,139 @@
+/**
+ * scripts/region-geo.test.ts — validation for the committed
+ * `public/region-geo.json` (built by `scripts/build-region-geo.mjs`).
+ *
+ * The manifest maps each region key to its { area (km²), population } — the
+ * weighting source for the per-region stats model (v0.28, #46): a nation's
+ * four 0–100 stats are derived as the area×population-weighted median of the
+ * stats of the regions it owns. It is a load-bearing data artifact — this
+ * test pins its contract.
+ *
+ * The `area` is the turf area of the region's final geometry (km², 2 dp); the
+ * `population` is the country's Natural-Earth admin-0 `POP_EST` (from the
+ * committed `public/ne-admin0-pop.json`) distributed across its sub-regions
+ * proportional to area via largest-remainder, so every country's sub-regions
+ * sum EXACTLY to the country's total (and the global total is the sum over the
+ * 177 repo countries). This is a dependency-free test: it reads the JSON with
+ * plain `fs`/`JSON.parse` (no `@turf`/geojson types, which would pull
+ * `@types/geojson` into the tsc program and break `WorldMap.tsx` — see the
+ * v0.17 note). The determinism test re-runs the (turf `.mjs`) builder and
+ * compares bytes, matching that the builder is idempotent.
+ */
+import { readFileSync } from 'node:fs';
+import { execFileSync } from 'node:child_process';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+
+function readJson(rel: string): Record<string, unknown> {
+  return JSON.parse(readFileSync(path.join(root, rel), 'utf8'));
+}
+
+interface GeoEntry {
+  area: number;
+  population: number;
+}
+
+// The 177 repo countries' admin-0 population totals (the committed derived
+// source). Only the countries actually present in the region dataset appear.
+const admin0 = readJson('public/ne-admin0-pop.json') as Record<string, number>;
+// feature id -> region key
+const manifest = readJson('public/region-keys.json') as Record<string, string>;
+// feature id -> { name, parent (ISO_A3) }
+const regGeo = readJson('public/regions.geo.json') as {
+  features?: Array<{ id?: string | number; properties?: { name?: string; parent?: string } }>;
+};
+
+// region key -> parent ISO_A3 (via the key manifest + the geo feature parent).
+const keyToParent: Record<string, string> = {};
+for (const f of regGeo.features ?? []) {
+  const key = manifest[String(f.id)];
+  const parent = f.properties?.parent;
+  if (key && parent) keyToParent[key] = parent;
+}
+
+const geo = readJson('public/region-geo.json') as Record<string, GeoEntry>;
+const keys = Object.values(manifest);
+
+describe('region-geo.json', () => {
+  it('has exactly one entry per region key (same key set as region-keys.json)', () => {
+    expect(new Set(Object.keys(geo))).toEqual(new Set(keys));
+    expect(Object.keys(geo)).toHaveLength(1800);
+  });
+
+  it('is keyed in sorted (deterministic) order', () => {
+    const ks = Object.keys(geo);
+    expect(ks).toEqual([...ks].sort());
+  });
+
+  it('every entry is a finite { area ≥ 0 with ≤ 2 dp, integer population ≥ 0 }', () => {
+    for (const [k, v] of Object.entries(geo)) {
+      expect(Number.isFinite(v.area), `non-finite area for ${k}`).toBe(true);
+      expect(Number.isFinite(v.population), `non-finite population for ${k}`).toBe(true);
+      expect(v.area >= 0, `negative area for ${k}: ${v.area}`).toBe(true);
+      // area is recorded to at most 2 decimal places (km²)
+      expect(Math.round(v.area * 100) / 100 === v.area, `area over 2dp for ${k}: ${v.area}`).toBe(true);
+      expect(Number.isInteger(v.population), `non-integer population for ${k}: ${v.population}`).toBe(true);
+      expect(v.population >= 0, `negative population for ${k}: ${v.population}`).toBe(true);
+    }
+  });
+
+  it('the global population total equals the sum of the 177 repo countries\' admin-0 totals', () => {
+    // The distribution preserved each country's total exactly, so the grand
+    // total over all sub-regions is the sum over the repo countries only.
+    const total = Object.values(geo).reduce((s, v) => s + v.population, 0);
+    expect(total).toBe(7654092021);
+  });
+
+  it('preserves each country\'s population total across its sub-regions (largest-remainder)', () => {
+    // For every parent country present in the region dataset, the sum of its
+    // sub-regions' populations must equal that country's admin-0 POP_EST
+    // EXACTLY — this is the invariant the largest-remainder distribution
+    // guarantees (no population is created or lost by the split).
+    const byParent: Record<string, number> = {};
+    for (const [k, v] of Object.entries(geo)) {
+      const p = keyToParent[k];
+      if (!p) throw new Error(`no parent for region key ${k}`);
+      byParent[p] = (byParent[p] ?? 0) + v.population;
+    }
+    expect(Object.keys(byParent).length).toBe(177); // the 177 repo countries
+    for (const [p, sum] of Object.entries(byParent)) {
+      expect(admin0[p], `missing admin-0 population for ${p}`).toBeDefined();
+      expect(sum, `population drift for ${p}: sub-regions ${sum} vs admin-0 ${admin0[p]}`).toBe(admin0[p]);
+    }
+  });
+
+  it('spot-checks well-known regions for exact area + population', () => {
+    const is = (k: string, area: number, population: number) => {
+      const v = geo[k];
+      expect(v, `missing geo for ${k}`).toBeDefined();
+      expect(v!.area, `area for ${k}`).toBe(area);
+      expect(v!.population, `population for ${k}`).toBe(population);
+    };
+    is('california-kikh', 413329.21, 14184195); // US-CA
+    is('arkhangel-sk-lhbk', 305257.7, 2579108); // RU-ARK mainland core
+    is('pechora-qwhs', 37399.76, 315989); // RU-PEO (Arctic-coast band, #41)
+    is('yamal-gosw', 50598.25, 427502); // RU-YAM (Arctic-coast band, #41)
+    is('new-earth-eikt', 15721.27, 132828); // RU-ARK-NE (island group, #31)
+    is('severnaya-zemlya-awqp', 1209.93, 10223); // RU-ARK-SZ (island group, #31)
+    is('ain-lqtt', 22557.77, 2304126); // FR-01 (Ain)
+  });
+
+  it('is deterministic: re-running the builder rewrites a byte-identical file', () => {
+    const file = path.join(root, 'public', 'region-geo.json');
+    const before = readFileSync(file, 'utf8');
+    // The builder is cwd-independent (it resolves the repo root from its own
+    // location) and idempotent: same input files (regions.geo.json +
+    // region-keys.json + ne-admin0-pop.json) + pure turf + fixed 2-dp rounding
+    // + stable (sorted) key order → identical bytes.
+    execFileSync(process.execPath, [path.join(root, 'scripts', 'build-region-geo.mjs')], {
+      cwd: root,
+      stdio: 'pipe',
+    });
+    const after = readFileSync(file, 'utf8');
+    expect(after).toBe(before);
+  });
+});

scripts/region-keys.test.ts

@@ -33,13 +33,13 @@ describe('region-keys.json', () => {
   const keys = Object.values(manifest);
   const featureIds = (geo.features ?? []).map((f) => String(f.id));
 
-  it('has exactly 1,796 entries (one per region)', () => {
-    expect(Object.keys(manifest)).toHaveLength(1796);
+  it('has exactly 1,800 entries (one per region)', () => {
+    expect(Object.keys(manifest)).toHaveLength(1800);
   });
 
-  it('has 1,796 unique keys (no collisions)', () => {
+  it('has 1,800 unique keys (no collisions)', () => {
     expect(new Set(keys).size).toBe(keys.length);
-    expect(new Set(keys).size).toBe(1796);
+    expect(new Set(keys).size).toBe(1800);
   });
 
   it('keys each end in -[a-z]{4} and contain at least one hyphen', () => {
@@ -50,11 +50,26 @@ describe('region-keys.json', () => {
     }
   });
 
+  it("keeps RU-ARK's key stable across the #31 + #41 splits and mints the island and band keys", () => {
+    // v0.25 (#31) split RU-ARK into main + RU-ARK-NE + RU-ARK-SZ, and v0.26
+    // (#41) repartitioned the mainland into the core (RU-ARK) + RU-PEO +
+    // RU-YAM. The MAIN feature keeps its id (and therefore its key — FNV-1a
+    // of the id), which is what keeps existing Nation.territory / SQLite
+    // ownership valid; the new features get fresh keys derived the same way
+    // from their ids (no within-country name-collision salt needed — the
+    // slugs are unique).
+    expect(manifest['RU-ARK']).toBe('arkhangel-sk-lhbk'); // unchanged since v0.19
+    expect(manifest['RU-ARK-NE']).toBe('new-earth-eikt');
+    expect(manifest['RU-ARK-SZ']).toBe('severnaya-zemlya-awqp');
+    expect(manifest['RU-PEO']).toBe('pechora-qwhs');
+    expect(manifest['RU-YAM']).toBe('yamal-gosw');
+  });
+
   it('is a stable join: its keys are exactly the regions.geo.json feature ids', () => {
     // The manifest is looked up by feature id, so its key set must line up
     // 1:1 with the geo file (catches drift if the geo is regenerated without
     // rebuilding the keys).
-    expect(featureIds).toHaveLength(1796);
+    expect(featureIds).toHaveLength(1800);
     const manifestIds = Object.keys(manifest);
     expect(new Set(manifestIds)).toEqual(new Set(featureIds));
   });

scripts/regions.test.ts

@@ -530,16 +530,22 @@ describe('regions.geo.json', () => {
     );
   });
 
-  it('is at the v0.17 fixed point: 1,796 regions, 11,794 parts, 11,795 rings, 164,801 vertices, 1 hole (KZ-KZY)', () => {
+  it('is at the v0.26 fixed point: 1,800 regions, 11,794 parts, 11,795 rings, 164,801 vertices, 1 hole (KZ-KZY)', () => {
     // v0.17 (scripts/fill-gaps.mjs) APPENDED cleaned gap pieces to the v0.16
     // fixed point: it never moves an existing border, merges a part, or
     // removes a ring — it only adds new parts (+6,768: 5,026 → 11,794) and
-    // keeps the single KZ-KZY hole. The region count (1,796), the
-    // per-feature ids/names/parents and their order are unchanged; only the
-    // part/ring/vertex totals and the hole's part structure moved. Pinning
-    // the signature guards against a non-idempotent or destructive re-run.
-    // The fill is byte-deterministic per input and idempotent (a second run
-    // on the filled file changes nothing).
+    // keeps the single KZ-KZY hole. The v0.25 Arkhangel'sk split (#31,
+    // scripts/split-arkhangel.mjs) then repartitioned the 78 RU-ARK parts
+    // across three features (RU-ARK + RU-ARK-NE + RU-ARK-SZ), and the v0.26
+    // band split (#41, scripts/split-arkhangel-band.mjs) repartitioned the
+    // 33-part mainland again into RU-ARK + RU-PEO + RU-YAM. Both are pure
+    // re-groupings: no part/ring/vertex moves, so only the region count
+    // changed (1,796 → 1,798 → 1,800); the part/ring/vertex totals, the
+    // per-feature ids/names/parents, and the feature order (the new features
+    // sit immediately after RU-ARK-SZ) are as pinned below. Pinning the
+    // signature guards against a non-idempotent or destructive re-run; both
+    // stages are byte-deterministic per input and idempotent (a second run
+    // changes nothing).
     const polysOf = (g: Geometry) => (g.type === 'Polygon' ? [g.coordinates] : g.coordinates);
     let verts = 0,
       rings = 0,
@@ -556,15 +562,67 @@ describe('regions.geo.json', () => {
         for (const ring of poly) verts += ring.length;
       }
     }
-    expect(regions.features.length, 'region count').toBe(1796); // unchanged by the fill
-    expect(parts, 'parts').toBe(11_794); // v0.16: 5,026 → +6,768 appended gap pieces
+    expect(regions.features.length, 'region count').toBe(1800); // 1,796 + the #31 islands (+2) + the #41 band regions (+2)
+    expect(parts, 'parts').toBe(11_794); // v0.16: 5,026 → +6,768 appended gap pieces; unchanged by the #31/#41 re-partitions
     expect(rings, 'rings').toBe(11_795); // every appended part is a single-ring polygon (+1 hole = KZ-KZY, pre-existing)
     expect(holes, 'holes').toBe(1); // the single KZ-KZY hole, unchanged
     expect(holeIds, 'the one remaining hole is KZ-KZY').toEqual(['KZ-KZY']);
-    expect(verts, 'total vertices (incl. ring closure)').toBe(164_801); // v0.16: 111,175
+    expect(verts, 'total vertices (incl. ring closure)').toBe(164_801); // v0.16: 111,175; unchanged by the #31/#41 re-partitions
     console.log(
-      `\n  v0.17 gap fill: ${regions.features.length} regions, ${parts} parts, ${rings} rings, ` +
-        `${holes} hole (KZ-KZY), ${verts} vertices — v0.16 topology preserved, 6,768 gap pieces appended`,
+      `\n  v0.26 fixed point: ${regions.features.length} regions (1,796 + the #31 islands + the #41 band), ` +
+        `${parts} parts, ${rings} rings, ${holes} hole (KZ-KZY), ${verts} vertices — v0.17 topology preserved`,
+    );
+  });
+
+  it('has the five Arkhangel\'sk-family features: #31 islands + #41 band (RU-ARK, New Earth, Severnaya Zemlya, Pechora, Yamal)', () => {
+    // v0.25 (#31): the ~411,500 km² RU-ARK mega-region (a 78-part MultiPolygon
+    // mixing mainland and far-north islands) was repartitioned by part
+    // centroid into the mainland (RU-ARK, keeps its id/name/key), the Franz
+    // Josef Land islets (RU-ARK-NE "New Earth", centroid lat ≥ 79.5) and the
+    // Severnaya Zemlya islets (RU-ARK-SZ, centroid 76–79.5° N, lon ≥ 55°E).
+    // v0.26 (#41): the 33-part mainland (post-#31) was repartitioned again —
+    // the 5 lat < 68 parts stay RU-ARK (id/name/key unchanged), and the 28
+    // lat ≥ 68 "Arctic-coast band" parts split into RU-PEO "Pechora" (the SW
+    // Voronoi cell, 13 parts) and RU-YAM "Yamal" (the NE Voronoi cell, 15
+    // parts). Pure re-grouping: all five keep parent RUS and all 78 original
+    // parts of the pre-#31 feature are accounted for, verbatim.
+    const byId = new Map(regions.features.map((f) => [f.id, f]));
+    const ark = byId.get('RU-ARK');
+    const ne = byId.get('RU-ARK-NE');
+    const sz = byId.get('RU-ARK-SZ');
+    const peo = byId.get('RU-PEO');
+    const yam = byId.get('RU-YAM');
+    for (const f of [ark, ne, sz, peo, yam]) {
+      expect(f, `${f?.id ?? '?'} exists`).toBeDefined();
+      expect(f!.properties.parent, `${f!.id} parent`).toBe('RUS');
+      expect(f!.geometry.type, `${f!.id} geometry`).toBe('MultiPolygon');
+    }
+    expect(ark!.properties.name, 'RU-ARK keeps its name').toBe("Arkhangel'sk");
+    expect(ne!.properties.name, 'RU-ARK-NE name').toBe('New Earth');
+    expect(sz!.properties.name, 'RU-ARK-SZ name').toBe('Severnaya Zemlya');
+    expect(peo!.properties.name, 'RU-PEO name').toBe('Pechora');
+    expect(yam!.properties.name, 'RU-YAM name').toBe('Yamal');
+    // the 78 parts of the pre-split feature are all accounted for, verbatim
+    const countParts = (f: (typeof regions.features)[number]) =>
+      f.geometry.type === 'MultiPolygon' ? f.geometry.coordinates.length : 1;
+    expect(
+      countParts(ark!) + countParts(ne!) + countParts(sz!) + countParts(peo!) + countParts(yam!),
+      'total parts across the five features',
+    ).toBe(78);
+    // the #41 split: the mainland core keeps its 5 lat < 68 parts; the band's
+    // 28 parts split 13 (Pechora) / 15 (Yamal)
+    expect(countParts(ark!), 'RU-ARK core part count').toBe(5);
+    expect(countParts(peo!), 'RU-PEO part count').toBe(13);
+    expect(countParts(yam!), 'RU-YAM part count').toBe(15);
+    // stable file order: RU-ARK, RU-ARK-NE, RU-ARK-SZ, RU-PEO, RU-YAM
+    const idx = regions.features.findIndex((f) => f.id === 'RU-ARK');
+    expect(regions.features[idx + 1]?.id).toBe('RU-ARK-NE');
+    expect(regions.features[idx + 2]?.id).toBe('RU-ARK-SZ');
+    expect(regions.features[idx + 3]?.id).toBe('RU-PEO');
+    expect(regions.features[idx + 4]?.id).toBe('RU-YAM');
+    console.log(
+      `\n  #31 + #41: RU-ARK ${countParts(ark!)} parts (core), RU-ARK-NE ${countParts(ne!)} (New Earth), ` +
+        `RU-ARK-SZ ${countParts(sz!)} (Severnaya Zemlya), RU-PEO ${countParts(peo!)} (Pechora), RU-YAM ${countParts(yam!)} (Yamal)`,
     );
   });
 });

scripts/split-arkhangel-band.mjs

@@ -0,0 +1,247 @@
+#!/usr/bin/env node
+/**
+ * scripts/split-arkhangel-band.mjs — split the RU-ARK Arctic-coast band into
+ * two new regions, RU-PEO ("Pechora", the SW group) and RU-YAM ("Yamal", the
+ * NE group) (issue #41, a follow-up to #31).
+ *
+ * The #31 split (`scripts/split-arkhangel.mjs`) left `RU-ARK` as a 33-part
+ * MultiPolygon (~393,256 km²). Measured on that feature (centroid latitude /
+ * planar area), the parts divide cleanly by centroid latitude:
+ *
+ *   lat < 68            4 parts  ~305,000 km²  (Arkhangel'sk proper + 3 slivers)
+ *   66 ≤ lat < 68       1 part   ~47 km²
+ *   lat ≥ 68            28 parts ~88,000 km²   (the "Arctic-coast band")
+ *
+ * The band is really *other* Arctic oblasts (Nenets / Pechora / Yamal / Taimyr
+ * side) mis-lumped into Arkhangel'sk during the v0.14 coarsening. This stage
+ * re-coarsens it: the 28 band parts are split into two new regions by a
+ * Voronoi of the two band parts with the largest planar area (the SW anchor
+ * vs the NE anchor), while the 5 lat < 68 parts stay in `RU-ARK`.
+ *
+ *   RU-ARK   (keeps its id and name)  — the 5 lat < 68 parts (original order)
+ *                                          → still the `arkhangel-sk-lhbk` key
+ *   RU-PEO   "Pechora"                — the band's SW Voronoi cell (13 parts)
+ *   RU-YAM   "Yamal"                  — the band's NE Voronoi cell (15 parts)
+ *
+ * Deterministic, turf-free threshold spec (all data-derived — no magic
+ * coordinates; the same planar model the tests/adjacency build use):
+ *   1. centroid of a part = the mean of its outer-ring vertices (verified to
+ *      give the same band assignment as turf's area-weighted centroid, 0 flips).
+ *   2. band = the parts whose centroid lat ≥ 68 (asserted to be exactly 28).
+ *   3. anchors = the 2 band parts with the largest planar area (≈ 47,223 and
+ *      ≈ 32,907 km², indices 2 and 1 in the 33-part feature); anchorW = the
+ *      anchor with the smaller centroid longitude.
+ *   4. each non-anchor band part → the nearer anchor by km-weighted centroid
+ *      distance, `dist(a,b) = hypot(Δlon·111.32·cos(midLat), Δlat·110.574)`;
+ *      a tie → west (anchorW). Each anchor → its own group. This yields
+ *      PEO = {1,4,5,9,11,12,13,14,16,17,18,20,22} and
+ *      YAM = {2,6,15,19,21,23,24,25,26,27,28,29,30,31,32} (0-based indices).
+ *
+ * PURE REPARTITION — no geometry is created, moved, or altered: each part is
+ * moved verbatim (same coordinates, same ring order) from the one feature to
+ * the others. The union of the three output geometries is byte-identical to
+ * the input feature's parts, so no border moves and no new overlap is
+ * possible (the same guarantee as #31). `RU-ARK` keeps its stable feature id,
+ * so its region key (`arkhangel-sk-lhbk`, FNV-1a of the id) and every existing
+ * `Nation.territory` / SQLite ownership referencing it stays valid; the two
+ * new ids (`RU-PEO`, `RU-YAM`) get their own keys derived by the same FNV-1a
+ * rule in `scripts/build-region-keys.mjs` (`pechora-qwhs`, `yamal-gosw` —
+ * run it after this stage).
+ *
+ * The new features are inserted immediately after `RU-ARK-SZ` (stable file
+ * order, deterministic bytes: `RU-ARK, RU-ARK-NE, RU-ARK-SZ, RU-PEO, RU-YAM,
+ * …`). Each new feature's `properties` copies `RU-ARK`'s (only `name` and
+ * `parent` exist in this dataset) with `name` overridden; `parent` stays RUS.
+ * Each feature's geometry is a MultiPolygon of its assigned parts (in
+ * original order), or a single Polygon if it ended up with one part (it won't
+ * here, but the builder handles it).
+ *
+ * Pipeline position: AFTER `split-arkhangel` and BEFORE `build-region-keys`
+ * (the manifests must be rebuilt after any geo change):
+ *
+ *   generate → coarsen → cleanup → smooth → fill-gaps → split-arkhangel
+ *   → **split-arkhangel-band** → build-region-keys → build-region-adjacency
+ *
+ * Idempotent: when RU-PEO and RU-YAM already exist the file is left untouched
+ * (no write at all), so a full re-run of the pipeline reproduces byte-identical
+ * output.
+ *
+ * Usage:  node scripts/split-arkhangel-band.mjs [inFile [outFile]]
+ *          (or `npm run split:regions:band`)
+ *   inFile  default: public/regions.geo.json
+ *   outFile default: inFile (edit in place)
+ *
+ * Deliberately turf-free: no `@turf/*` import (turf is only ever imported by
+ * the geo-generator `.mjs` stages, never by this re-partition or by any `.ts`).
+ */
+import { readFileSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+const inFile = process.argv[2] ?? path.join(root, 'public', 'regions.geo.json');
+const outFile = process.argv[3] ?? inFile;
+
+// A part whose centroid lat is ≥ this is part of the Arctic-coast band; the
+// lat < 68 core stays in RU-ARK (issue #41).
+const BAND_MIN_LAT = 68;
+
+// The post-#31 mainland feature is a 33-part MultiPolygon; any other shape
+// means the file is not the state this stage expects → fail loud.
+const EXPECTED_PARTS = 33;
+// The Arctic-coast band is exactly 28 of those parts (lat ≥ 68).
+const EXPECTED_BAND = 28;
+
+// Planar km model (matches the test's area model and the adjacency build):
+// x = lon · 111.32 · cos(midLat), y = lat · 110.574.
+const KM_LON = 111.32;
+const KM_LAT = 110.574;
+const rad = (deg) => (deg * Math.PI) / 180;
+
+/**
+ * Mean of a part's outer-ring vertices — a turf-free centroid. Verified to give
+ * the same band assignment as turf's area-weighted centroid (0 flips).
+ */
+function centroidOf(part) {
+  const ring = part[0];
+  let lon = 0;
+  let lat = 0;
+  for (const [lo, la] of ring) {
+    lon += lo;
+    lat += la;
+  }
+  return [lon / ring.length, lat / ring.length];
+}
+
+/** Planar area of a part (km²), shoelace over its outer ring at its mean latitude. */
+function areaKm2(part) {
+  const ring = part[0];
+  let lat = 0;
+  for (const [, la] of ring) lat += la;
+  const midLat = lat / ring.length;
+  const kx = KM_LON * Math.cos(rad(midLat));
+  let a = 0;
+  for (let i = 0; i < ring.length; i++) {
+    const [lon1, lat1] = ring[i];
+    const [lon2, lat2] = ring[(i + 1) % ring.length];
+    a += lon1 * kx * (lat2 * KM_LAT) - lon2 * kx * (lat1 * KM_LAT);
+  }
+  return Math.abs(a / 2);
+}
+
+/** Planar km distance between two centroids (midpoint-latitude weighted). */
+function kmDist(a, b) {
+  const dLon = b[0] - a[0];
+  const dLat = b[1] - a[1];
+  const midLat = (a[1] + b[1]) / 2;
+  return Math.hypot(dLon * KM_LON * Math.cos(rad(midLat)), dLat * KM_LAT);
+}
+
+// --- load --------------------------------------------------------------------
+const geo = JSON.parse(readFileSync(inFile, 'utf8'));
+if (geo?.type !== 'FeatureCollection' || !Array.isArray(geo.features)) {
+  throw new Error(`${inFile} is not a FeatureCollection`);
+}
+const features = geo.features;
+
+// --- idempotency: already split? ----------------------------------------------
+const ids = new Set(features.map((f) => String(f.id ?? '')));
+if (ids.has('RU-PEO') && ids.has('RU-YAM')) {
+  console.log(
+    `[split-arkhangel-band] RU-PEO and RU-YAM already present — no-op (idempotent), ${inFile} left untouched`,
+  );
+  process.exit(0);
+}
+
+// --- load + validate RU-ARK ---------------------------------------------------
+const idx = features.findIndex((f) => f.id === 'RU-ARK');
+if (idx < 0) throw new Error('RU-ARK not found in ' + inFile);
+const ark = features[idx];
+if (ark.geometry?.type !== 'MultiPolygon') {
+  throw new Error(
+    `RU-ARK geometry is ${ark.geometry?.type}, expected MultiPolygon (the 33-part post-#31 mainland)`,
+  );
+}
+const parts = ark.geometry.coordinates;
+if (parts.length !== EXPECTED_PARTS) {
+  throw new Error(`RU-ARK has ${parts.length} parts, expected ${EXPECTED_PARTS} (the post-#31 mainland)`);
+}
+
+// --- band selection (centroid lat ≥ 68) and the lat < 68 core -----------------
+const partsByIndex = parts.map((p, i) => ({ i, c: centroidOf(p) }));
+const band = partsByIndex.filter((o) => o.c[1] >= BAND_MIN_LAT);
+if (band.length !== EXPECTED_BAND) {
+  throw new Error(`expected exactly ${EXPECTED_BAND} Arctic-coast band parts (lat ≥ ${BAND_MIN_LAT}), found ${band.length}`);
+}
+const core = partsByIndex.filter((o) => o.c[1] < BAND_MIN_LAT);
+
+// --- anchors: the two band parts with the largest planar area -----------------
+// (≈ 47,223 and ≈ 32,907 km², indices 2 and 1 in the 33-part feature).
+const byArea = [...band].sort((a, b) => areaKm2(parts[b.i]) - areaKm2(parts[a.i]));
+const big = byArea[0];
+const small = byArea[1];
+const anchorW = big.c[0] <= small.c[0] ? big : small; // the west (SW) anchor
+const anchorE = big.c[0] <= small.c[0] ? small : big; // the east (NE) anchor
+
+// --- assignment (Voronoi by km-weighted centroid distance; tie → west) --------
+const peo = new Set([anchorW.i]);
+const yam = new Set([anchorE.i]);
+for (const o of band) {
+  if (o.i === anchorW.i || o.i === anchorE.i) continue;
+  const dW = kmDist(o.c, anchorW.c);
+  const dE = kmDist(o.c, anchorE.c);
+  (dW <= dE ? peo : yam).add(o.i); // a tie goes to the west (anchorW) group
+}
+
+// --- rebuild geometries (parts verbatim, original order; MultiPolygon/Polygon) --
+const geom = (ps) =>
+  ps.length > 1 ? { type: 'MultiPolygon', coordinates: ps } : { type: 'Polygon', coordinates: ps[0] };
+
+const coreParts = [...core].sort((a, b) => a.i - b.i).map((o) => parts[o.i]);
+const peoParts = [...peo].sort((a, b) => a - b).map((i) => parts[i]);
+const yamParts = [...yam].sort((a, b) => a - b).map((i) => parts[i]);
+
+ark.geometry = geom(coreParts);
+
+const mkFeature = (id, name, ps) => ({
+  type: 'Feature',
+  id,
+  // copy every property RU-ARK has (currently just { name, parent }), overriding name
+  properties: { ...ark.properties, name },
+  geometry: geom(ps),
+});
+const peoF = mkFeature('RU-PEO', 'Pechora', peoParts);
+const yamF = mkFeature('RU-YAM', 'Yamal', yamParts);
+
+// --- report -------------------------------------------------------------------
+const km2 = (ps) => ps.reduce((s, p) => s + areaKm2(p), 0);
+console.log(`[split-arkhangel-band] input: ${inFile}`);
+console.log(
+  `  RU-ARK  (core, lat < 68)   ${coreParts.length} parts (of ${parts.length}), ≈ ${Math.round(km2(coreParts)).toLocaleString('en-US')} km²`,
+);
+console.log(
+  `  RU-PEO  (Pechora, SW)      ${peoParts.length} parts, ≈ ${Math.round(km2(peoParts)).toLocaleString('en-US')} km²  [${[...peo].sort((a, b) => a - b).join(',')}]`,
+);
+console.log(
+  `  RU-YAM  (Yamal, NE)        ${yamParts.length} parts, ≈ ${Math.round(km2(yamParts)).toLocaleString('en-US')} km²  [${[...yam].sort((a, b) => a - b).join(',')}]`,
+);
+if (peoParts.length === 0 || yamParts.length === 0) {
+  throw new Error(
+    `threshold mis-split: Pechora=${peoParts.length} parts, Yamal=${yamParts.length} parts — check the band before shipping`,
+  );
+}
+
+// --- insert at a stable position (immediately after RU-ARK-SZ) and write -------
+// RU-ARK-SZ must exist (the #31 split ran first); if it doesn't, this stage is
+// being run out of order → fail loud.
+const szIdx = features.findIndex((f) => f.id === 'RU-ARK-SZ');
+if (szIdx < 0) {
+  throw new Error('RU-ARK-SZ not found — the #31 split (scripts/split-arkhangel.mjs) must run before this stage');
+}
+features.splice(szIdx + 1, 0, peoF, yamF);
+writeFileSync(outFile, JSON.stringify(geo));
+console.log(
+  `[split-arkhangel-band] wrote ${outFile} — features ${features.length - 2} → ${features.length}` +
+    ` (order …, RU-ARK, RU-ARK-NE, RU-ARK-SZ, RU-PEO, RU-YAM, …)`,
+);

scripts/split-arkhangel.mjs

@@ -0,0 +1,180 @@
+#!/usr/bin/env node
+/**
+ * scripts/split-arkhangel.mjs — split the RU-ARK ("Arkhangel'sk") mega-region
+ * into main + two detached island archipelagos (issue #31).
+ *
+ * `RU-ARK` is a 78-part MultiPolygon of ~411,500 km²: the Arkhangel'sk
+ * mainland plus Arctic-coast mainland parts, tiny islets, AND two far-north
+ * island groups that belong nowhere near the mainland — the Franz Josef Land
+ * islets (New Earth, centroid lat ≥ 79.5) and the Severnaya Zemlya islets
+ * (centroid lat 76–79.5, lon ≥ 55). This stage repartitions the existing
+ * polygon parts between three features so each island group is its own
+ * addressable sub-region:
+ *
+ *   RU-ARK     (keeps its id and name)  — every part whose centroid has
+ *                                         lat < 76 (the mainland, Arctic-coast
+ *                                         mainland parts, islets, one south dot)
+ *   RU-ARK-NE  "New Earth"              — every part whose centroid has
+ *                                         lat ≥ 79.5 (the 42 Franz Josef Land
+ *                                         islets, ~15,700 km²)
+ *   RU-ARK-SZ  "Severnaya Zemlya"       — every part whose centroid has
+ *                                         76 ≤ lat < 79.5 AND lon ≥ 55 (the 3
+ *                                         Severnaya Zemlya islets, ~1,200 km²)
+ *
+ * (Parts in the 76–79.5° band with lon < 55 would stay in RU-ARK; none exist
+ * in the current dataset — the split is verified clean before it is written.)
+ *
+ * PURE REPARTITION — no geometry is created, moved, or altered: each part is
+ * moved verbatim (same coordinates, same ring order) from the one feature to
+ * the other. The union of the three output geometries is byte-identical to
+ * the input feature's parts, so no border moves and no new overlap is
+ * possible. RU-ARK keeps its stable feature id, so its region key
+ * (`arkhangel-sk-lhbk`, FNV-1a of the id) and every existing
+ * `Nation.territory` / SQLite ownership referencing it stays valid; the two
+ * new ids (`RU-ARK-NE`, `RU-ARK-SZ`) get their own keys derived by the same
+ * FNV-1a rule in `scripts/build-region-keys.mjs` (run it after this stage).
+ *
+ * The new features are inserted immediately after RU-ARK (stable file order,
+ * deterministic bytes). Each new feature's `properties` copies RU-ARK's
+ * (only `name` and `parent` exist in this dataset) with `name` overridden;
+ * `parent` stays RUS. Each feature's geometry is a MultiPolygon of its
+ * assigned parts, or a single Polygon if it ends up with one part.
+ *
+ * Pipeline position: between `fill-gaps` and `build-region-keys` (the
+ * manifests must be rebuilt after any geo change):
+ *
+ *   generate → coarsen → cleanup → smooth → fill-gaps → **split-arkhangel**
+ *   → build-region-keys → build-region-adjacency
+ *
+ * Idempotent: when RU-ARK-NE and RU-ARK-SZ already exist the file is left
+ * untouched (no write at all), so a full re-run of the pipeline reproduces
+ * byte-identical output.
+ *
+ * Usage:  node scripts/split-arkhangel.mjs [inFile [outFile]]
+ *          (or `npm run split:regions`)
+ *   inFile  default: public/regions.geo.json
+ *   outFile default: inFile (edit in place)
+ *
+ * `@turf/centroid` + `@turf/helpers` are used only to classify each part by
+ * its centroid — the same measurement the split thresholds are defined in.
+ * (Turf is allowed in .mjs scripts only; never imported by any .ts file.)
+ */
+import { readFileSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import centroid from '@turf/centroid';
+import area from '@turf/area';
+import { polygon } from '@turf/helpers';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const root = path.resolve(here, '..');
+const inFile = process.argv[2] ?? path.join(root, 'public', 'regions.geo.json');
+const outFile = process.argv[3] ?? inFile;
+
+// The split thresholds (degrees), per issue #31.
+const NEW_EARTH_MIN_LAT = 79.5; // centroid lat ≥ this → New Earth (Franz Josef Land)
+const SZ_BAND_MIN_LAT = 76; // centroid lat ≥ this (and < NEW_EARTH_MIN_LAT)…
+const SZ_MIN_LON = 55; // …and centroid lon ≥ this → Severnaya Zemlya
+// (anything else — including the 76–79.5° band west of 55°E, of which the
+// current dataset has none — stays in the main Arkhangel'sk feature)
+
+/** A GeoJSON polygon part as a turf Feature (for centroid/area only). */
+const partFeature = (part) => polygon(part);
+
+/**
+ * A part's centroid [lon, lat]. Strict by design: a centroid that cannot be
+ * computed is a data error, not something to silently route to the mainland.
+ */
+function centroidOf(part) {
+  try {
+    return centroid(partFeature(part)).geometry.coordinates;
+  } catch (err) {
+    throw new Error(`cannot compute centroid for a RU-ARK part: ${err.message}`);
+  }
+}
+
+/** Classify a centroid [lon, lat] into one of the three output buckets. */
+function bucketOf([lon, lat]) {
+  if (lat >= NEW_EARTH_MIN_LAT) return 'ne';
+  if (lat >= SZ_BAND_MIN_LAT && lat < NEW_EARTH_MIN_LAT && lon >= SZ_MIN_LON) return 'sz';
+  return 'main';
+}
+
+// --- load --------------------------------------------------------------------
+const geo = JSON.parse(readFileSync(inFile, 'utf8'));
+if (geo?.type !== 'FeatureCollection' || !Array.isArray(geo.features)) {
+  throw new Error(`${inFile} is not a FeatureCollection`);
+}
+const features = geo.features;
+
+// --- idempotency: already split? ----------------------------------------------
+const ids = new Set(features.map((f) => String(f.id ?? '')));
+if (ids.has('RU-ARK-NE') && ids.has('RU-ARK-SZ')) {
+  console.log(
+    `[split-arkhangel] RU-ARK-NE and RU-ARK-SZ already present — no-op (idempotent), ${inFile} left untouched`,
+  );
+  process.exit(0);
+}
+
+const idx = features.findIndex((f) => f.id === 'RU-ARK');
+if (idx < 0) {
+  throw new Error('RU-ARK not found in ' + inFile);
+}
+const ark = features[idx];
+if (ark.geometry?.type !== 'MultiPolygon') {
+  throw new Error(
+    `RU-ARK geometry is ${ark.geometry?.type}, expected MultiPolygon (the split expects the pre-#31 mega-region)`,
+  );
+}
+const parts = ark.geometry.coordinates;
+
+// --- partition (stable: original part order is kept inside each bucket) -------
+const buckets = { main: [], ne: [], sz: [] };
+let bandWest = 0; // 76–79.5°-band parts west of 55°E (stay in main; 0 in the current data)
+for (const part of parts) {
+  const [lon, lat] = centroidOf(part);
+  if (lat >= SZ_BAND_MIN_LAT && lat < NEW_EARTH_MIN_LAT && lon < SZ_MIN_LON) bandWest += 1;
+  buckets[bucketOf([lon, lat])].push(part);
+}
+
+// --- rebuild geometries (parts verbatim; MultiPolygon, or Polygon if 1 part) --
+const geom = (ps) =>
+  ps.length > 1
+    ? { type: 'MultiPolygon', coordinates: ps }
+    : { type: 'Polygon', coordinates: ps[0] };
+
+ark.geometry = geom(buckets.main);
+
+const mkFeature = (id, name, ps) => ({
+  type: 'Feature',
+  id,
+  // copy every property RU-ARK has (currently just { name, parent }), overriding name
+  properties: { ...ark.properties, name },
+  geometry: geom(ps),
+});
+const ne = mkFeature('RU-ARK-NE', 'New Earth', buckets.ne);
+const sz = mkFeature('RU-ARK-SZ', 'Severnaya Zemlya', buckets.sz);
+
+// --- report -------------------------------------------------------------------
+const km2 = (ps) => ps.reduce((s, p) => s + area(partFeature(p)) * 1e-6, 0);
+console.log(`[split-arkhangel] input: ${inFile}`);
+console.log(
+  `  RU-ARK    (main)  ${buckets.main.length} parts (of ${parts.length}), ≈ ${Math.round(km2(buckets.main)).toLocaleString('en-US')} km²` +
+    (bandWest ? ` — incl. ${bandWest} part(s) in the 76–79.5° band west of 55°E (kept in main)` : ''),
+);
+console.log(
+  `  RU-ARK-NE (New Earth)         ${buckets.ne.length} parts, ≈ ${Math.round(km2(buckets.ne)).toLocaleString('en-US')} km²`,
+);
+console.log(
+  `  RU-ARK-SZ (Severnaya Zemlya)  ${buckets.sz.length} parts, ≈ ${Math.round(km2(buckets.sz)).toLocaleString('en-US')} km²`,
+);
+if (buckets.ne.length === 0 || buckets.sz.length === 0) {
+  throw new Error(
+    `threshold mis-split: New Earth=${buckets.ne.length} parts, Severnaya Zemlya=${buckets.sz.length} parts — check the centroids before shipping`,
+  );
+}
+
+// --- insert at a stable position (immediately after RU-ARK) and write ---------
+features.splice(idx + 1, 0, ne, sz);
+writeFileSync(outFile, JSON.stringify(geo));
+console.log(`[split-arkhangel] wrote ${outFile} — features ${features.length - 2} → ${features.length}`);

server/db.test.ts

@@ -25,6 +25,12 @@ function makeState(id: string): GameState {
     version: 1,
     unowned: [],
     pendingNationOps: [],
+    markers: [],
+    // (v0.28, #46) a v0.28+ save carries per-region stats; the fake 'GBR'
+    // region here holds a copy of the uk's (single-region) stats.
+    regionStats: {
+      GBR: { military: 80, economy: 70, stability: 60, population: 50 },
+    },
   };
 }
 
@@ -97,6 +103,50 @@ describe('openDb', () => {
     db.close();
   });
 
+  it('(v0.27 #44) a legacy row saved before the markers field existed loads with it defaulted to []', () => {
+    const db = openDb(':memory:');
+    const legacy = makeState('legacy');
+    delete (legacy as { markers?: unknown[] }).markers; // a pre-v0.27 save (field absent)
+    db.save(legacy);
+    const loaded = db.load('legacy');
+    expect(loaded).not.toBeNull();
+    expect(loaded!.markers).toEqual([]);
+    db.close();
+  });
+
+  it('(v0.28 #46) a legacy row saved before the regionStats field existed loads with it seeded per region and stats recomputed', () => {
+    const db = openDb(':memory:');
+    const legacy = makeState('legacy');
+    delete (legacy as { regionStats?: Record<string, unknown> }).regionStats; // a pre-v0.28 save (field absent)
+    db.save(legacy);
+    const loaded = db.load('legacy');
+    expect(loaded).not.toBeNull();
+    // each owned region is seeded with a copy of its owner's stats…
+    expect(loaded!.regionStats).toEqual({
+      GBR: { military: 80, economy: 70, stability: 60, population: 50 },
+    });
+    // …and a single-region nation's derived stats equal the seeded ones
+    // (the weighted median of identical values is that value).
+    expect(loaded!.nations.uk.stats).toEqual({ military: 80, economy: 70, stability: 60, population: 50 });
+    db.close();
+  });
+
+  it('(v0.28 #46) a v0.28+ row (regionStats present) loads UNCHANGED — no recompute on load', () => {
+    const db = openDb(':memory:');
+    const s = makeState('current');
+    // Diverge one region's stats from the nation level to prove load does not
+    // recompute (a v0.28+ save keeps its stored derived stats exactly).
+    s.regionStats = { GBR: { military: 99, economy: 70, stability: 60, population: 50 } };
+    s.nations = { uk: { ...s.nations.uk, stats: { military: 42, economy: 70, stability: 60, population: 50 } } };
+    db.save(s);
+    const loaded = db.load('current');
+    expect(loaded).not.toBeNull();
+    expect(loaded!.regionStats).toEqual({ GBR: { military: 99, economy: 70, stability: 60, population: 50 } });
+    // the nation's stats are NOT recomputed from the region on load (they stay 42)
+    expect(loaded!.nations.uk.stats.military).toBe(42);
+    db.close();
+  });
+
   it('delete removes a game by id and reports absence otherwise', () => {
     const db = openDb(':memory:');
     db.save(makeState('a'));

server/db.ts

@@ -2,6 +2,7 @@
 import { mkdirSync } from 'node:fs';
 import path from 'node:path';
 import Database from 'better-sqlite3';
+import { migrateRegionStats } from '../shared/protocol';
 import type { GameState } from '../shared/types';
 
 export interface Db {
@@ -39,13 +40,22 @@ export function openDb(filePath: string): Db {
       const row = byId.get(id) as { data: string } | undefined;
       if (!row) return null;
       try {
-        const state = JSON.parse(row.data) as GameState;
+        let state = JSON.parse(row.data) as GameState;
         // (v0.22, #16 P3) Rows saved before `GameState.unowned` existed load
         // with it defaulted: a legacy game has no no-man's-land regions.
         if (state.unowned === undefined) state.unowned = [];
         // (v0.23, #16 P4a) Same for pending nation-op proposals: a legacy game
         // has none awaiting confirm/reject.
         if (state.pendingNationOps === undefined) state.pendingNationOps = [];
+        // (v0.27, #44) Same for map markers: a legacy game has none placed.
+        if (state.markers === undefined) state.markers = [];
+        // (v0.28, #46) Rows saved before per-region stats existed are migrated
+        // ONCE at load time (and never re-migrated afterwards — the field is
+        // then present): each owned region is seeded with a copy of its owner's
+        // nation-level stats and the nations' stats are recomputed as the
+        // (uniform-weight) area×population-weighted median, so no data is lost
+        // and a single-region nation keeps exactly its old stats.
+        state = migrateRegionStats(state);
         return state;
       } catch {
         return null;

server/engine.test.ts

@@ -1,16 +1,19 @@
 import { describe, expect, it } from 'vitest';
-import type { GameState, Preset, RoundItem } from '../shared/types';
-import { makeEvent, type NationOp, type TurnResult } from '../shared/protocol';
+import type { GameState, MarkerType, Nation, NationStats, Preset, RegionStats, RoundItem } from '../shared/types';
+import { makeEvent, markerId, MAX_MARKERS, seedRegionStats, type MarkerSpec, type NationOp, type TurnResult } from '../shared/protocol';
 import type { LlmClient, ToolDefinition, WireMessage } from './llm';
 import { makeStubLlmClient } from './stub';
 import {
+  applyNationOp,
   applyTurnResult,
   buildSystemPrompt,
   buildUserPrompt,
   confirmNationOp,
+  freshNationId,
   GET_NEIGHBOURS_TOOL,
   isMeaningful,
   makeNeighboursExecutor,
+  NEW_NATION_STATS,
   parseTurnResult,
   playerFrontier,
   queueRoundItem,
@@ -18,6 +21,7 @@ import {
   removeRoundItem,
   resolveNationRef,
   runTurn,
+  validateMarkerOps,
   validateNationOps,
   validateTurnResult,
 } from './engine';
@@ -67,6 +71,11 @@ const preset: Preset = {
 };
 
 function baseState(): GameState {
+  const nations: GameState['nations'] = {
+    uk: { ...preset.nations[0], stats: { ...preset.nations[0].stats }, territory: [...preset.nations[0].territory], relations: { ...preset.nations[0].relations } },
+    us: { ...preset.nations[1], stats: { ...preset.nations[1].stats }, territory: [...preset.nations[1].territory], relations: { ...preset.nations[1].relations } },
+    de: { ...preset.nations[2], stats: { ...preset.nations[2].stats }, territory: [...preset.nations[2].territory], relations: { ...preset.nations[2].relations } },
+  };
   return {
     id: 'g1',
     presetId: 'test',
@@ -74,16 +83,16 @@ function baseState(): GameState {
     playerNationId: 'uk',
     turn: 1,
     date: '1939-09-01',
-    nations: {
-      uk: { ...preset.nations[0], stats: { ...preset.nations[0].stats }, territory: [...preset.nations[0].territory], relations: { ...preset.nations[0].relations } },
-      us: { ...preset.nations[1], stats: { ...preset.nations[1].stats }, territory: [...preset.nations[1].territory], relations: { ...preset.nations[1].relations } },
-      de: { ...preset.nations[2], stats: { ...preset.nations[2].stats }, territory: [...preset.nations[2].territory], relations: { ...preset.nations[2].relations } },
-    },
+    nations,
     events: [],
     pending: [],
     version: 1,
     unowned: [],
     pendingNationOps: [],
+    markers: [],
+    // (v0.28, #46) every owned region starts as a copy of its owner's stats,
+    // so a fresh state's derived stats equal its nation-level stats.
+    regionStats: seedRegionStats(nations),
   };
 }
 
@@ -521,7 +530,7 @@ describe('validateNationOps (v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'France', to: 'French Republic' }],
+      nationOps: [{ kind: 'rename', nationRef: 'France', to: 'French Republic' }], markers: { add: [], remove: [] },
     });
     expect(withOps).not.toBeNull();
     expect(withOps!.nationOps).toEqual([{ kind: 'rename', nationRef: 'France', to: 'French Republic' }]);
@@ -542,7 +551,7 @@ describe('applyTurnResult (nation-op proposals, v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }],
+      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], markers: { add: [], remove: [] },
     });
     expect(next.nations.de.name).toBe('DE'); // still the old name
     expect(next.pendingNationOps).toEqual([{ kind: 'rename', nationRef: 'de', to: 'Reich' }]);
@@ -562,7 +571,7 @@ describe('applyTurnResult (nation-op proposals, v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'us', to: 'USA' }], // new proposal this turn
+      nationOps: [{ kind: 'rename', nationRef: 'us', to: 'USA' }], markers: { add: [], remove: [] }, // new proposal this turn
     });
     expect(next.pendingNationOps).toEqual([
       { kind: 'rename', nationRef: 'de', to: 'Reich' }, // the old one survived
@@ -580,7 +589,7 @@ describe('applyTurnResult (nation-op proposals, v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }],
+      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], markers: { add: [], remove: [] },
     });
     expect(next.pendingNationOps).toEqual([{ kind: 'rename', nationRef: 'de', to: 'Reich' }]);
   });
@@ -634,7 +643,7 @@ describe('confirmNationOp / rejectNationOp (v0.23 #16 P4a)', () => {
     expect(next!.nations.us.name).toBe('United States');
   });
 
-  it('confirm is a no-op on the world for a P4b-kind op (split/merge) — the op is still removed', () => {
+  it('confirm of a 1-part split is a no-op on the world (fewer than 2 parts) — the op is still removed', () => {
     const state = baseState();
     state.pendingNationOps = [{ kind: 'split', nationRef: 'de', parts: [{ name: 'East' }] }];
     const next = confirmNationOp(state, 0);
@@ -683,18 +692,306 @@ describe('confirmNationOp / rejectNationOp (v0.23 #16 P4a)', () => {
   });
 });
 
-describe('buildSystemPrompt (nationOps contract, v0.23 #16 P4a)', () => {
-  it('both modes contract the nationOps field and the rename proposal rule', () => {
+describe('buildSystemPrompt (nationOps contract, v0.23 #16 P4a; v0.24 #16 P4b)', () => {
+  it('both modes contract the nationOps field with all three op kinds and the proposal rule', () => {
     for (const p of [buildSystemPrompt(preset), buildSystemPrompt(preset, true)]) {
-      // the JSON shape carries the field in both modes
-      expect(p).toMatch(/"nationOps": \[\{"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"\}\]/);
-      // the rule explains that it is a proposal only the player can confirm
+      // the JSON shape carries all three kinds in both modes
+      expect(p).toMatch(/"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"/);
+      expect(p).toMatch(/"kind":"split","nationRef":"<nation id or name>","parts":\[\{"name":"<new name>","territory":\["<region key>"\]\}\]/);
+      expect(p).toMatch(/"kind":"merge","nationRefs":\["<id>","<id>"\],"survivingRef":"<id of the surviving nation>","into":"<new name>"/);
+      // the rule explains that ops are proposals only the player can confirm
       expect(p).toMatch(/PROPOSAL/);
-      expect(p).toMatch(/only takes effect if the player confirms/);
+      expect(p).toMatch(/only take effect if the player confirms/);
+      // and the split/merge shapes are spelt out in the hard constraints
+      expect(p).toMatch(/at least 2 parts/);
+      expect(p).toMatch(/survivingRef" must name one of them/);
     }
   });
 });
 
+describe('freshNationId (v0.24 #16 P4b)', () => {
+  it('returns the first free of n1, n2, ... against the taken set', () => {
+    expect(freshNationId(new Set())).toBe('n1');
+    expect(freshNationId(new Set(['n1']))).toBe('n2');
+    expect(freshNationId(new Set(['n1', 'n2', 'n3']))).toBe('n4');
+    // non-n ids never collide: existing nation ids are irrelevant
+    expect(freshNationId(new Set(['uk', 'de', 'us']))).toBe('n1');
+  });
+});
+
+describe('applyNationOp (split, v0.24 #16 P4b)', () => {
+  /** de owns four regions; the player is uk (so a split of de does not move the pointer). */
+  function splitState(): GameState {
+    const s = baseState();
+    s.nations.de.territory = ['DEU-N', 'DEU-S', 'DEU-E', 'DEU-W'];
+    s.nations.de.relations = { uk: 'ally' };
+    s.nations.uk.relations.de = 'hostile'; // mirror entry, to check the cleanup
+    return s;
+  }
+
+  it('partitions the parent territory: first-wins per key, leftovers to part 0, fresh ids, baseline stats, copied relations, parent removed', () => {
+    const state = splitState();
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'de',
+      parts: [
+        { name: 'East', territory: ['DEU-E', 'DEU-W', 'ZZZ-not-a-key'] },
+        { name: 'West', territory: ['DEU-W', 'DEU-S'] },
+      ],
+    });
+    // the parent is gone and two fresh nations exist (n1, n2 — uk/us/de were taken)
+    expect(state.nations.de).toBeUndefined();
+    expect(Object.keys(state.nations).sort()).toEqual(['n1', 'n2', 'uk', 'us']);
+    const east = state.nations.n1;
+    const west = state.nations.n2;
+    // East claimed DEU-E and DEU-W first (the invalid key is ignored); the
+    // only key no part claimed — DEU-N (DEU-S went to West) — goes to part 0
+    // in the parent's territory order.
+    expect(east.territory).toEqual(['DEU-E', 'DEU-W', 'DEU-N']);
+    // West's DEU-W was already claimed by East; it keeps only DEU-S.
+    expect(west.territory).toEqual(['DEU-S']);
+    // every parent key sits in exactly one part (sole ownership, nothing lost)
+    const all = [...east.territory, ...west.territory].sort();
+    expect(all).toEqual(['DEU-E', 'DEU-N', 'DEU-S', 'DEU-W']);
+    // fresh baseline stats (not the parent's) and inherited form of state
+    expect(east.stats).toEqual(NEW_NATION_STATS);
+    expect(west.stats).toEqual(NEW_NATION_STATS);
+    expect(east.type).toBe('major');
+    expect(west.type).toBe('major');
+    // both parts copied the parent's relations
+    expect(east.relations).toEqual({ uk: 'ally' });
+    expect(west.relations).toEqual({ uk: 'ally' });
+    // the mirror entry for the removed parent is cleaned up
+    expect(state.nations.uk.relations.de).toBeUndefined();
+    expect(state.nations.uk.relations.us).toBe('neutral'); // other entries untouched
+    // the player (uk) is not affected
+    expect(state.playerNationId).toBe('uk');
+  });
+
+  it('an unresolvable nationRef is a no-op (the world is untouched, never throws)', () => {
+    const state = splitState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'zzz-not-a-nation',
+      parts: [{ name: 'East' }, { name: 'West' }],
+    });
+    expect(state).toEqual(before);
+  });
+
+  it('a split named by the parent NAME works (ref resolution, not just id)', () => {
+    const state = splitState();
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'DE', // the name; the id is 'de'
+      parts: [{ name: 'East', territory: ['DEU-E'] }, { name: 'West', territory: ['DEU-W'] }],
+    });
+    expect(state.nations.de).toBeUndefined();
+    expect(state.nations.n1.name).toBe('East');
+    expect(state.nations.n2.name).toBe('West');
+  });
+
+  it('when the parent is the player nation, playerNationId moves to the chosen part (edits.playerPart: default 0, clamped in range)', () => {
+    const state = splitState();
+    state.playerNationId = 'de';
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'de',
+      parts: [{ name: 'East' }, { name: 'West' }, { name: 'Centre' }],
+    });
+    expect(state.playerNationId).toBe('n1'); // default: the first part
+
+    const state2 = splitState();
+    state2.playerNationId = 'de';
+    applyNationOp(
+      state2,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }, { name: 'Centre' }],
+      },
+      { playerPart: 1 },
+    );
+    expect(state2.playerNationId).toBe('n2');
+
+    const state3 = splitState();
+    state3.playerNationId = 'de';
+    applyNationOp(
+      state3,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { playerPart: 99 }, // clamped down to the last part
+    );
+    expect(state3.playerNationId).toBe('n2');
+
+    const state4 = splitState();
+    state4.playerNationId = 'de';
+    applyNationOp(
+      state4,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { playerPart: -5 }, // clamped up to the first part
+    );
+    expect(state4.playerNationId).toBe('n1');
+  });
+
+  it('edits.name renames the chosen part (edits.playerPart picks which one)', () => {
+    const state = splitState();
+    applyNationOp(
+      state,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { playerPart: 1, name: 'New West' },
+    );
+    expect(state.nations.n1.name).toBe('East'); // untouched part keeps its name
+    expect(state.nations.n2.name).toBe('New West');
+
+    const state2 = splitState();
+    applyNationOp(
+      state2,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { name: 'First of the Remnant' }, // no playerPart -> the first part
+    );
+    expect(state2.nations.n1.name).toBe('First of the Remnant');
+    expect(state2.nations.n2.name).toBe('West');
+  });
+
+  it('a 1-part split is a no-op on the world (fewer than 2 parts)', () => {
+    const state = splitState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, { kind: 'split', nationRef: 'de', parts: [{ name: 'East' }] });
+    expect(state).toEqual(before);
+  });
+});
+
+describe('applyNationOp (merge, v0.24 #16 P4b)', () => {
+  /**
+   * de and us will be merged (the survivor is us — deliberately listed
+   * second in nationRefs, so the "survivor's view wins" rule can be observed
+   * overwriting the first input's views). uk, fr and ja survive as third
+   * parties; the survivor has no view on ja, so ja must come from the first
+   * input's map.
+   */
+  function mergeState(): GameState {
+    const s = baseState();
+    s.nations.de.relations = { us: 'rival', uk: 'hostile', fr: 'rival', ja: 'rival' };
+    s.nations.us.relations = { de: 'ally', uk: 'ally', fr: 'neutral' }; // no view on ja
+    s.nations.uk.relations = { us: 'ally', de: 'hostile', fr: 'neutral', ja: 'neutral' };
+    s.nations.fr = {
+      id: 'fr',
+      type: 'major',
+      name: 'FR',
+      stats: { military: 40, economy: 60, stability: 70, population: 60 },
+      territory: ['FRA'],
+      relations: { us: 'neutral', de: 'rival', uk: 'neutral', ja: 'neutral' },
+    };
+    s.nations.ja = {
+      id: 'ja',
+      type: 'major',
+      name: 'JA',
+      stats: { military: 30, economy: 80, stability: 50, population: 90 },
+      territory: ['JPN'],
+      relations: { us: 'neutral', de: 'rival', uk: 'neutral', fr: 'neutral' },
+    };
+    return s;
+  }
+
+  it('folds the inputs into the survivor: union territory (survivor first), survivor stats, survivor view wins per third party (else first input), non-input third parties kept, removed ids dropped from everyone else, into-name', () => {
+    const state = mergeState();
+    applyNationOp(state, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' });
+    // the removed input is gone; the survivor and all non-inputs survive
+    expect(state.nations.de).toBeUndefined();
+    expect(Object.keys(state.nations).sort()).toEqual(['fr', 'ja', 'uk', 'us']);
+    // the survivor keeps its id, its own stats, and the merged name
+    expect(state.nations.us.id).toBe('us');
+    expect(state.nations.us.stats).toEqual({ military: 60, economy: 90, stability: 80, population: 80 });
+    expect(state.nations.us.name).toBe('Union');
+    // territory: the union — the survivor's keys first, then the other input's
+    expect(state.nations.us.territory).toEqual(['USA', 'DEU']);
+    // relations: on uk and fr the survivor's own views (ally/neutral) beat the
+    // first input's (hostile/rival); ja has no survivor view, so the first
+    // input's (rival) stands; the removed input's id is gone from the map.
+    expect(state.nations.us.relations).toEqual({ uk: 'ally', fr: 'neutral', ja: 'rival' });
+    // the removed id is dropped from every remaining nation's relations map
+    expect(state.nations.uk.relations).toEqual({ us: 'ally', fr: 'neutral', ja: 'neutral' });
+    expect(state.nations.fr.relations).toEqual({ us: 'neutral', uk: 'neutral', ja: 'neutral' });
+    expect(state.nations.ja.relations).toEqual({ us: 'neutral', uk: 'neutral', fr: 'neutral' });
+    // the player (uk) is not part of the merge — the pointer stays valid
+    expect(state.playerNationId).toBe('uk');
+  });
+
+  it('the player pointer moves to the survivor when the player led a removed input', () => {
+    const state = mergeState();
+    state.playerNationId = 'de'; // the player's nation is absorbed
+    applyNationOp(state, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' });
+    expect(state.playerNationId).toBe('us');
+    expect(state.nations[state.playerNationId].name).toBe('Union');
+  });
+
+  it('edits.name overrides the merged name; an empty edit falls back to "into", then to the survivor name', () => {
+    const state = mergeState();
+    applyNationOp(state, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' }, { name: 'United World' });
+    expect(state.nations.us.name).toBe('United World');
+
+    const state2 = mergeState();
+    applyNationOp(state2, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' }, { name: '   ' });
+    expect(state2.nations.us.name).toBe('Union');
+
+    const state3 = mergeState();
+    applyNationOp(state3, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: '' }); // empty into: keep the survivor's name
+    expect(state3.nations.us.name).toBe('US');
+  });
+
+  it('an unresolvable input ref is a no-op (never throws, world untouched)', () => {
+    const state = mergeState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'merge',
+      nationRefs: ['us', 'zzz-not-a-nation'],
+      survivingRef: 'uk',
+      into: 'X',
+    });
+    expect(state).toEqual(before);
+  });
+
+  it('a survivor that is not one of the inputs is a no-op', () => {
+    const state = mergeState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'merge',
+      nationRefs: ['us', 'de'],
+      survivingRef: 'uk', // uk is not an input
+      into: 'X',
+    });
+    expect(state).toEqual(before);
+  });
+
+  it('fewer than two DISTINCT inputs is a no-op (the same nation named twice)', () => {
+    const state = mergeState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'merge',
+      nationRefs: ['us', 'US'], // both resolve to 'us'
+      survivingRef: 'us',
+      into: 'X',
+    });
+    expect(state).toEqual(before);
+  });
+});
+
 describe('parseTurnResult', () => {
   it('parses a fenced JSON block', () => {
     const r = parseTurnResult('```json\n{"date":"1939-09-03","events":[{"nation":"uk","type":"military","title":"t","text":"b","outcome":"success"}]}\n```');
@@ -748,7 +1045,7 @@ describe('applyTurnResult', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [],
+      nationOps: [], markers: { add: [], remove: [] },
     };
     applyTurnResult(state, result);
     expect(JSON.stringify(state)).toBe(snapshot);
@@ -764,7 +1061,7 @@ describe('applyTurnResult', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [],
+      nationOps: [], markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
     expect(next.pending).toEqual([]);
@@ -786,7 +1083,7 @@ describe('applyTurnResult', () => {
       // is not a real key at all. Both are proposed as a gain by DE.
       territoryChanges: [{ nation: 'de', gain: ['wales-bbbb', 'not-a-region-xyz'], lose: [] }],
       unowned: [],
-      nationOps: [],
+      nationOps: [], markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result, new Set(['wales-bbbb']));
     // the valid key was gained (taken from its sole previous owner); the bogus one was ignored
@@ -811,7 +1108,7 @@ describe('applyTurnResult', () => {
       // released (not in state.unowned), so it does not enter GameState.unowned.
       territoryChanges: [{ nation: 'de', gain: ['POL', 'wales-bbbb'], lose: [] }],
       unowned: [],
-      nationOps: [],
+      nationOps: [], markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result); // no validKeys -> nothing filtered
     expect(next.nations.de.territory).toContain('wales-bbbb');
@@ -828,7 +1125,7 @@ describe('applyTurnResult (sole-ownership invariants, v0.21 #16 P2)', () => {
     stateChanges: [],
     relations: [],
     unowned: [],
-    nationOps: [],
+    nationOps: [], markers: { add: [], remove: [] },
   };
 
   it('a double claim (two different gainers, one key) is rejected: the key stays with its original owner', () => {
@@ -917,7 +1214,7 @@ describe('applyTurnResult (no man\'s land, v0.22 #16 P3)', () => {
     relations: [],
     territoryChanges: [],
     unowned: [],
-    nationOps: [],
+    nationOps: [], markers: { add: [], remove: [] },
   };
 
   it('a release removes the key from its sole owner and marks it in GameState.unowned', () => {
@@ -1032,7 +1329,7 @@ describe('applyTurnResult (no man\'s land, v0.22 #16 P3)', () => {
 
   it('a lone release is meaningful (it survives the retry/nudge path)', () => {
     expect(
-      isMeaningful({ date: 'x', events: [], stateChanges: [], relations: [], territoryChanges: [], unowned: ['GBR'], nationOps: [] }),
+      isMeaningful({ date: 'x', events: [], stateChanges: [], relations: [], territoryChanges: [], unowned: ['GBR'], nationOps: [], markers: { add: [], remove: [] } }),
     ).toBe(true);
   });
 
@@ -1339,9 +1636,9 @@ describe('buildSystemPrompt (tool mode, v0.21 #16 P2)', () => {
 
 describe('isMeaningful', () => {
   it('is true with an event, false when everything is empty', () => {
-    expect(isMeaningful({ date: 'x', events: [{ nation: 'uk', type: 'military', title: 't', text: 'b', outcome: 'neutral' }], stateChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [] })).toBe(true);
-    expect(isMeaningful({ date: 'x', events: [], stateChanges: [{ nation: 'uk', stat: 'military', op: 'set', value: 5 }], relations: [], territoryChanges: [], unowned: [], nationOps: [] })).toBe(true);
-    expect(isMeaningful({ date: 'x', events: [], stateChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [] })).toBe(false);
+    expect(isMeaningful({ date: 'x', events: [{ nation: 'uk', type: 'military', title: 't', text: 'b', outcome: 'neutral' }], stateChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], markers: { add: [], remove: [] } })).toBe(true);
+    expect(isMeaningful({ date: 'x', events: [], stateChanges: [{ nation: 'uk', stat: 'military', op: 'set', value: 5 }], relations: [], territoryChanges: [], unowned: [], nationOps: [], markers: { add: [], remove: [] } })).toBe(true);
+    expect(isMeaningful({ date: 'x', events: [], stateChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], markers: { add: [], remove: [] } })).toBe(false);
   });
 
   it('(v0.23 #16 P4a) a turn that only proposes a nation-op is meaningful (it survives the retry/nudge path)', () => {
@@ -1353,8 +1650,473 @@ describe('isMeaningful', () => {
         relations: [],
         territoryChanges: [],
         unowned: [],
-        nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }],
+        nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], markers: { add: [], remove: [] },
+      }),
+    ).toBe(true);
+  });
+
+  it('(v0.27 #44) a turn that only adds a marker is meaningful (it survives the retry/nudge path)', () => {
+    expect(
+      isMeaningful({
+        date: 'x',
+        events: [],
+        stateChanges: [],
+        relations: [],
+        territoryChanges: [],
+        unowned: [],
+        nationOps: [],
+        markers: { add: [{ type: 'city', name: 'Lyon', regionKey: 'rhone-rhne' }], remove: [] },
       }),
     ).toBe(true);
   });
 });
+
+describe('markers (point placement, v0.27 #44)', () => {
+  // a deterministic centroid for one region key, undefined for everything else
+  const centroidOf = (key: string) =>
+    key === 'moselle-rygy' ? { lat: 48, lon: 6, spread: 1 } : undefined;
+
+  // build a MarkerSpec from a (possibly invalid, for the guard tests) type string
+  const mk = (type: string, name: string, regionKey: string): MarkerSpec =>
+    ({ type: type as MarkerType, name, regionKey });
+
+  it('adds a valid marker with a stable id, a jittered position within the spread, the region owner, and the placed turn', () => {
+    const state = baseState();
+    state.turn = 4; // placedTurn should equal the resolved turn
+    state.nations.uk.territory = ['GBR', 'moselle-rygy']; // the region is owned by uk
+    const result: TurnResult = {
+      date: '1939-09-03',
+      events: [],
+      stateChanges: [],
+      relations: [],
+      territoryChanges: [],
+      unowned: [],
+      nationOps: [],
+      markers: { add: [mk('city', 'Strasbourg', 'moselle-rygy')], remove: [] },
+    };
+    const next = applyTurnResult(state, result, undefined, centroidOf);
+    expect(next.markers).toHaveLength(1);
+    const m = next.markers[0];
+    expect(m.id).toBe(markerId('city', 'Strasbourg', 'moselle-rygy'));
+    expect(m.type).toBe('city');
+    expect(m.name).toBe('Strasbourg');
+    expect(m.regionKey).toBe('moselle-rygy');
+    expect(m.ownerNationId).toBe('uk'); // the region's sole owner
+    expect(m.placedTurn).toBe(4);
+    // the position is the centroid jittered within ±spread/2
+    expect(m.lat).toBeGreaterThanOrEqual(47.5);
+    expect(m.lat).toBeLessThanOrEqual(48.5);
+    expect(m.lon).toBeGreaterThanOrEqual(5.5);
+    expect(m.lon).toBeLessThanOrEqual(6.5);
+  });
+
+  it('is idempotent: re-adding the same (type, name, regionKey) does not duplicate the marker', () => {
+    const state = baseState();
+    state.nations.uk.territory = ['moselle-rygy'];
+    const add = [mk('city', 'Strasbourg', 'moselle-rygy')];
+    const first = applyTurnResult(state, {
+      date: '1939-09-03', events: [], stateChanges: [], relations: [], territoryChanges: [],
+      unowned: [], nationOps: [], markers: { add, remove: [] },
+    }, undefined, centroidOf);
+    expect(first.markers).toHaveLength(1);
+    // a second turn proposes the exact same marker again
+    const second = applyTurnResult(first, {
+      date: '1939-09-05', events: [], stateChanges: [], relations: [], territoryChanges: [],
+      unowned: [], nationOps: [], markers: { add, remove: [] },
+    }, undefined, centroidOf);
+    expect(second.markers).toHaveLength(1);
+    expect(second.markers[0].id).toBe(first.markers[0].id); // stable id, no second copy
+  });
+
+  it('applyTurnResult drops a new add whose region is unknown or has no centroid, but keeps a valid one', () => {
+    const state = baseState();
+    state.nations.uk.territory = ['moselle-rygy'];
+    // validKeys knows two keys; the centroid resolves only the first.
+    const validKeys = new Set(['moselle-rygy', 'other-key']);
+    const centroidOf2 = (k: string) =>
+      k === 'moselle-rygy' ? { lat: 48, lon: 6, spread: 1 } : undefined;
+    const result: TurnResult = {
+      date: '1939-09-03',
+      events: [],
+      stateChanges: [],
+      relations: [],
+      territoryChanges: [],
+      unowned: [],
+      nationOps: [],
+      markers: {
+        add: [
+          { type: 'city', name: 'Good', regionKey: 'moselle-rygy' }, // valid + centroid → kept
+          { type: 'city', name: 'NoCent', regionKey: 'other-key' }, // in validKeys, no centroid → dropped
+          { type: 'city', name: 'Unknown', regionKey: 'zzz-not-a-key' }, // not in validKeys → dropped
+        ],
+        remove: [],
+      },
+    };
+    const next = applyTurnResult(state, result, validKeys, centroidOf2);
+    expect(next.markers).toHaveLength(1);
+    expect(next.markers[0].name).toBe('Good');
+  });
+
+  it('caps the total marker count at MAX_MARKERS, dropping the newest add that exceeds the cap', () => {
+    const state = baseState();
+    // pre-seed the state with MAX_MARKERS - 1 distinct markers
+    const seeded: typeof state.markers = [];
+    for (let i = 0; i < MAX_MARKERS - 1; i++) {
+      const k = `seed-${i}`;
+      seeded.push({
+        id: markerId('city', `S${i}`, k),
+        type: 'city',
+        name: `S${i}`,
+        regionKey: k,
+        lat: 0, lon: 0,
+        ownerNationId: null,
+        placedTurn: 1,
+      });
+    }
+    state.markers = seeded;
+    // a permissive centroid: every region key resolves
+    const anyCentroid = () => ({ lat: 0, lon: 0, spread: 0 });
+    const result: TurnResult = {
+      date: '1939-09-03',
+      events: [],
+      stateChanges: [],
+      relations: [],
+      territoryChanges: [],
+      unowned: [],
+      nationOps: [],
+      markers: {
+        add: [
+          { type: 'city', name: 'NewA', regionKey: 'new-a' },
+          { type: 'city', name: 'NewB', regionKey: 'new-b' },
+        ],
+        remove: [],
+      },
+    };
+    const next = applyTurnResult(state, result, undefined, anyCentroid);
+    expect(next.markers).toHaveLength(MAX_MARKERS); // capped, not MAX_MARKERS + 1
+    expect(next.markers.some((m) => m.name === 'NewA')).toBe(true); // the 1st new one kept
+    expect(next.markers.some((m) => m.name === 'NewB')).toBe(false); // the 2nd (over cap) dropped
+  });
+
+  it('removes a marker by id; removing an absent id is a no-op', () => {
+    const state = baseState();
+    state.nations.uk.territory = ['moselle-rygy'];
+    const idA = markerId('city', 'Strasbourg', 'moselle-rygy');
+    const idB = markerId('port', 'Dunkirk', 'moselle-rygy');
+    state.markers = [
+      { id: idA, type: 'city', name: 'Strasbourg', regionKey: 'moselle-rygy', lat: 48, lon: 6, ownerNationId: 'uk', placedTurn: 1 },
+      { id: idB, type: 'port', name: 'Dunkirk', regionKey: 'moselle-rygy', lat: 48, lon: 6, ownerNationId: 'uk', placedTurn: 1 },
+    ];
+    const next = applyTurnResult(state, {
+      date: '1939-09-03', events: [], stateChanges: [], relations: [], territoryChanges: [],
+      unowned: [], nationOps: [], markers: { add: [], remove: [idA, 'zzzz-not-there'] },
+    }, undefined, centroidOf);
+    expect(next.markers).toHaveLength(1);
+    expect(next.markers[0].id).toBe(idB); // only A removed; the bogus id was a no-op
+  });
+
+  it('a marker owner follows its region: released to no man\'s land → null; re-claimed → the new owner', () => {
+    const state = baseState();
+    state.nations.uk.territory = ['moselle-rygy'];
+    const idA = markerId('city', 'Strasbourg', 'moselle-rygy');
+    state.markers = [
+      { id: idA, type: 'city', name: 'Strasbourg', regionKey: 'moselle-rygy', lat: 48, lon: 6, ownerNationId: 'uk', placedTurn: 1 },
+    ];
+    // 1) uk releases the region → the marker becomes ownerless
+    const released = applyTurnResult(state, {
+      date: '1939-09-03', events: [], stateChanges: [], relations: [], territoryChanges: [],
+      unowned: ['moselle-rygy'], nationOps: [], markers: { add: [], remove: [] },
+    }, undefined, centroidOf);
+    expect(released.markers[0].ownerNationId).toBeNull();
+    // 2) de re-claims the region → the marker's owner follows to de
+    const reclaimed = applyTurnResult(released, {
+      date: '1939-09-05', events: [], stateChanges: [], relations: [],
+      territoryChanges: [{ nation: 'de', gain: ['moselle-rygy'], lose: [] }],
+      unowned: [], nationOps: [], markers: { add: [], remove: [] },
+    }, undefined, centroidOf);
+    expect(reclaimed.markers[0].ownerNationId).toBe('de');
+  });
+
+  it('the user prompt carries the existing markers when provided (and omits the field otherwise)', () => {
+    const state = baseState();
+    const info = {
+      id: markerId('city', 'Strasbourg', 'moselle-rygy'),
+      type: 'city' as MarkerType,
+      name: 'Strasbourg',
+      regionKey: 'moselle-rygy',
+      owner: 'uk',
+    };
+    const payload = JSON.parse(
+      buildUserPrompt(state, [], undefined, undefined, undefined, [info]),
+    ) as { markers?: Array<Record<string, unknown>> };
+    expect(payload.markers).toHaveLength(1);
+    expect(payload.markers![0].name).toBe('Strasbourg');
+    expect(payload.markers![0].owner).toBe('uk');
+    // a bare call (no markers arg) omits the field entirely
+    const bare = JSON.parse(buildUserPrompt(state, [])) as { markers?: unknown };
+    expect(bare.markers).toBeUndefined();
+  });
+
+  it('the system prompt documents the markers contract (field + placement rule + a type)', () => {
+    const prompt = buildSystemPrompt(preset);
+    expect(prompt).toMatch(/named points on the map/i);
+    expect(prompt).toMatch(/"markers"/);
+    expect(prompt).toMatch(/"add"/);
+    expect(prompt).toMatch(/"remove"/);
+    expect(prompt).toMatch(/gathering/);
+    expect(prompt).toMatch(/no man's land/); // owner recompute on release
+  });
+
+  it('validateMarkerOps cleans a raw markers field: drops bad types/empty names, dedupes, trims removes', () => {
+    const raw = {
+      add: [
+        { type: 'city', name: 'X', regionKey: 'a' },
+        { type: 'not-a-type', name: 'Y', regionKey: 'a' }, // invalid type -> dropped
+        { type: 'city', name: '   ', regionKey: 'a' }, // empty name -> dropped
+        { type: 'city', name: 'X', regionKey: 'a' }, // duplicate (same id) -> deduped
+        { type: 'port', name: 'Z', regionKey: 'b' }, // valid
+      ],
+      remove: ['id-1', 42, '', '  id-2  ', 'id-1'], // number/empty dropped, trimmed, deduped
+    };
+    const out = validateMarkerOps(raw);
+    expect(out.add.map((m) => m.name).sort()).toEqual(['X', 'Z']);
+    expect(out.remove).toEqual(['id-1', 'id-2']);
+  });
+
+  it('validateMarkerOps returns empty ops for a non-object raw value (a string, an array, null)', () => {
+    for (const bad of ['oops', [{ type: 'city', name: 'X', regionKey: 'a' }], null, undefined]) {
+      expect(validateMarkerOps(bad)).toEqual({ add: [], remove: [] });
+    }
+  });
+
+  it('runTurn wires the centroid through: a marker added over the LLM path is placed (owner = region owner)', async () => {
+    const result = JSON.stringify({
+      date: '1939-09-03',
+      events: [],
+      stateChanges: [],
+      relations: [],
+      territoryChanges: [{ nation: 'uk', gain: ['moselle-rygy'], lose: [] }],
+      unowned: [],
+      nationOps: [],
+      markers: { add: [{ type: 'city', name: 'Strasbourg', regionKey: 'moselle-rygy' }], remove: [] },
+    });
+    const { state } = await runTurn({
+      llm: fakeLlm([result]),
+      preset,
+      state: baseState(),
+      items: [],
+      centroidOf,
+    });
+    expect(state.markers).toHaveLength(1);
+    expect(state.markers[0].name).toBe('Strasbourg');
+    expect(state.markers[0].ownerNationId).toBe('uk'); // uk gained the region this turn
+  });
+});
+
+// --- Per-region stats (v0.28, #46): the derived-stats model ------------------
+//
+// A nation's 0–100 stats are DERIVED as the area×population-weighted median of
+// the stats of the regions it owns (`GameState.regionStats`). These tests pin
+// the turn-level maintenance of that model in `applyTurnResult`:
+//   - a transferred region keeps its OWN stats (the conquest is what makes a
+//     nation's regions diverge);
+//   - a released region's entry is deleted (no man's land carries none);
+//   - a re-claimed region with no entry is re-inited to the gainer's stats;
+//   - a 0-region nation keeps its (directly-maintained) stats;
+//   - the end-of-turn recompute weights by area×population when `geoOf` is
+//     provided (and degrades to a uniform median without it).
+//
+// `applyTurnResult` is used directly (not `runTurn`) so the tests are pure and
+// don't depend on the LLM: the result objects below are constructed directly.
+
+const NS = (military: number, economy: number, stability: number, population: number): NationStats => ({
+  military,
+  economy,
+  stability,
+  population,
+});
+
+const RS = (military: number, economy: number, stability: number, population: number): RegionStats => ({
+  military,
+  economy,
+  stability,
+  population,
+});
+
+function mkNation(id: string, stats: NationStats, territory: string[]): Nation {
+  return { id, name: id.toUpperCase(), type: 'major', stats, territory, relations: {} };
+}
+
+function mkTurnState(
+  nations: Record<string, Nation>,
+  regionStats: Record<string, RegionStats>,
+  unowned: string[] = [],
+): GameState {
+  return {
+    id: 'g',
+    presetId: 'p',
+    presetTitle: 'P',
+    playerNationId: Object.keys(nations)[0] ?? '',
+    turn: 1,
+    date: '1939-09-01',
+    nations,
+    events: [],
+    pending: [],
+    version: 1,
+    unowned,
+    pendingNationOps: [],
+    markers: [],
+    regionStats,
+  };
+}
+
+function mkTurnResult(partial: Partial<TurnResult>): TurnResult {
+  return {
+    date: '1939-09-03',
+    events: partial.events ?? [],
+    stateChanges: partial.stateChanges ?? [],
+    relations: partial.relations ?? [],
+    territoryChanges: partial.territoryChanges ?? [],
+    unowned: partial.unowned ?? [],
+    nationOps: partial.nationOps ?? [],
+    markers: partial.markers ?? { add: [], remove: [] },
+  };
+}
+
+describe('applyTurnResult — per-region stats (v0.28, #46)', () => {
+  it('a transferred region keeps its OWN stats; the conqueror\'s aggregate blends them', () => {
+    // uk owns g1 (military 80), de owns d1 (military 95). de conquers g1.
+    const state = mkTurnState(
+      {
+        uk: mkNation('uk', NS(80, 70, 60, 50), ['g1']),
+        de: mkNation('de', NS(95, 90, 75, 90), ['d1']),
+      },
+      {
+        g1: RS(80, 70, 60, 50),
+        d1: RS(95, 90, 75, 90),
+      },
+    );
+    const next = applyTurnResult(
+      state,
+      mkTurnResult({ territoryChanges: [{ nation: 'de', gain: ['g1'], lose: [] }] }),
+    );
+    // territory moved
+    expect(next.nations.uk.territory).toEqual([]);
+    expect(next.nations.de.territory).toEqual(['d1', 'g1']);
+    // the transferred region KEPT its own (uk's) stats — not re-inited to de's
+    expect(next.regionStats.g1).toEqual(RS(80, 70, 60, 50));
+    expect(next.regionStats.d1).toEqual(RS(95, 90, 75, 90));
+    // de's derived stats are the (uniform) median of its two regions → pulled
+    // toward the conquered region's lower values
+    expect(next.nations.de.stats).toEqual(RS(80, 70, 60, 50));
+    // uk (now 0 regions) keeps its directly-maintained stats untouched
+    expect(next.nations.uk.stats).toEqual(NS(80, 70, 60, 50));
+  });
+
+  it('a released region leaves no-man\'s land and its stats entry is deleted', () => {
+    const state = mkTurnState(
+      { uk: mkNation('uk', NS(80, 70, 60, 50), ['g1', 'g2']) },
+      { g1: RS(80, 70, 60, 50), g2: RS(60, 60, 60, 60) },
+    );
+    const next = applyTurnResult(state, mkTurnResult({ unowned: ['g1'] }));
+    expect(next.unowned).toEqual(['g1']);
+    expect(next.nations.uk.territory).toEqual(['g2']);
+    // g1's stats left the table with the region; g2's stay
+    expect(next.regionStats).toEqual({ g2: RS(60, 60, 60, 60) });
+    // uk's derived stats now come only from g2
+    expect(next.nations.uk.stats).toEqual(RS(60, 60, 60, 60));
+  });
+
+  it('a re-claimed region with no entry is re-inited to the gainer\'s current stats', () => {
+    // g1 is unowned (released earlier; its stats entry was deleted). de owns d1.
+    const deStats = NS(95, 90, 75, 90);
+    const state = mkTurnState(
+      {
+        uk: mkNation('uk', NS(80, 70, 60, 50), []),
+        de: mkNation('de', deStats, ['d1']),
+      },
+      { d1: RS(95, 90, 75, 90) }, // g1 has NO entry (it was released)
+      ['g1'],
+    );
+    const next = applyTurnResult(state, mkTurnResult({ territoryChanges: [{ nation: 'de', gain: ['g1'], lose: [] }] }));
+    expect(next.unowned).toEqual([]); // g1 leaves no man's land
+    expect(next.nations.de.territory).toEqual(['d1', 'g1']);
+    // g1 was re-inited as a copy of de's (pre-stateChanges) stats
+    expect(next.regionStats.g1).toEqual(RS(95, 90, 75, 90));
+    // both of de's regions now hold identical stats → derived stats = those stats
+    expect(next.nations.de.stats).toEqual(RS(95, 90, 75, 90));
+  });
+
+  it('a 0-region nation keeps its directly-maintained stats (the recompute skips it)', () => {
+    const state = mkTurnState(
+      { uk: mkNation('uk', NS(80, 70, 60, 50), []) },
+      {},
+    );
+    const next = applyTurnResult(
+      state,
+      mkTurnResult({ stateChanges: [{ nation: 'uk', stat: 'military', op: 'set', value: 99 }] }),
+    );
+    expect(next.nations.uk.territory).toEqual([]);
+    // no regions to aggregate → the nation-level update sticks
+    expect(next.nations.uk.stats.military).toBe(99);
+    expect(next.regionStats).toEqual({});
+  });
+
+  it('the recompute weights by area×population: the larger region dominates (geoOf)', () => {
+    // uk owns two regions: a small one (military 50) and a large one (military
+    // 90). With area×population weighting the large region's value wins; without
+    // geo the uniform median picks the lower value (reached first at half-weight).
+    const state = mkTurnState(
+      { uk: mkNation('uk', NS(50, 50, 50, 50), ['big', 'small']) },
+      { big: RS(90, 90, 90, 90), small: RS(50, 50, 50, 50) },
+    );
+    const geoOf = (k: string) =>
+      k === 'big' ? { area: 1000, population: 1000 } : { area: 10, population: 100 };
+
+    const weighted = applyTurnResult(state, mkTurnResult({}), undefined, undefined, geoOf);
+    expect(weighted.nations.uk.stats).toEqual(RS(90, 90, 90, 90)); // the large region dominates
+
+    const uniform = applyTurnResult(state, mkTurnResult({})); // no geoOf
+    expect(uniform.nations.uk.stats).toEqual(RS(50, 50, 50, 50)); // uniform → lower value first
+  });
+
+  it('a nation-level stat change re-applies to every owned region (before the recompute)', () => {
+    // uk owns two identical regions. A nation-level `add` applies to each region
+    // and the derived (uniform) median tracks it; a 0-region sibling keeps its
+    // own nation-level update.
+    const state = mkTurnState(
+      {
+        uk: mkNation('uk', NS(50, 50, 50, 50), ['a', 'b']),
+        de: mkNation('de', NS(50, 50, 50, 50), []),
+      },
+      { a: RS(50, 50, 50, 50), b: RS(50, 50, 50, 50) },
+    );
+    const next = applyTurnResult(
+      state,
+      mkTurnResult({
+        stateChanges: [
+          { nation: 'uk', stat: 'economy', op: 'add', value: 20 },
+          { nation: 'de', stat: 'military', op: 'set', value: 77 },
+        ],
+      }),
+    );
+    // uk: both regions +20 economy → derived economy 70
+    expect(next.regionStats.a).toEqual(RS(50, 70, 50, 50));
+    expect(next.regionStats.b).toEqual(RS(50, 70, 50, 50));
+    expect(next.nations.uk.stats).toEqual(RS(50, 70, 50, 50));
+    // de: 0 regions → its nation-level set sticks
+    expect(next.nations.de.stats.military).toBe(77);
+  });
+
+  it('the original state is never mutated', () => {
+    const state = mkTurnState(
+      { uk: mkNation('uk', NS(80, 70, 60, 50), ['g1']), de: mkNation('de', NS(95, 90, 75, 90), ['d1']) },
+      { g1: RS(80, 70, 60, 50), d1: RS(95, 90, 75, 90) },
+    );
+    const beforeNations = JSON.stringify(state.nations);
+    const beforeRegions = JSON.stringify(state.regionStats);
+    applyTurnResult(state, mkTurnResult({ territoryChanges: [{ nation: 'de', gain: ['g1'], lose: [] }] }));
+    expect(JSON.stringify(state.nations)).toBe(beforeNations);
+    expect(JSON.stringify(state.regionStats)).toBe(beforeRegions);
+  });
+});

server/engine.ts

@@ -7,6 +7,9 @@ import type {
   EventOutcome,
   EventType,
   GameState,
+  MapMarker,
+  Nation,
+  NationStats,
   Preset,
   RelationStatus,
   RoundItem,
@@ -16,9 +19,16 @@ import { EVENT_TYPES, RELATION_STATUSES } from '../shared/types';
 import {
   addDays,
   clampStat,
+  deriveNationStats,
+  fnv1a32,
   isDateLike,
+  isMarkerType,
   makeEvent,
+  markerId,
+  MAX_MARKERS,
   nationForPrompt,
+  type MarkerInfo,
+  type MarkerSpec,
   type NationOp,
   type TurnEventSpec,
   type TurnResult,
@@ -134,7 +144,9 @@ export function playerFrontier(
  * When `withNeighboursTool` is set (the turn runs with the getNeighbours tool
  * available) the contract gains the contiguity rules for territory transfers
  * (v0.21, #16 P2): the model may only move regions across a shared border, and
- * may verify borders with the tool before answering.
+ * may verify borders with the tool before answering. The contract also
+ * documents the `nationOps` proposal queue (v0.23, #16 P4a) — rename plus the
+ * split/merge shapes applied on player confirm (v0.24, #16 P4b).
  */
 export function buildSystemPrompt(preset: Preset, withNeighboursTool = false): string {
   const rules = preset.simulationRules
@@ -178,14 +190,23 @@ export function buildSystemPrompt(preset: Preset, withNeighboursTool = false): s
     '  "relations": [{"a":"<nationId>","b":"<nationId>","set":"<ally|neutral|rival|hostile|war>"}],',
     '  "territoryChanges": [{"nation":"<nationId>","gain":["<region key>"],"lose":["<region key>"]}],',
     '  "unowned": ["<region key>"],',
-    '  "nationOps": [{"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"}]',
+    '  "nationOps": [',
+    '    {"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"},',
+    '    {"kind":"split","nationRef":"<nation id or name>","parts":[{"name":"<new name>","territory":["<region key>"]}]}',
+    '    {"kind":"merge","nationRefs":["<id>","<id>"],"survivingRef":"<id of the surviving nation>","into":"<new name>"}',
+    '  ],',
+    '  "markers": {"add":[{"type":"<city|factory|army|port|capital|fleet|rocket|gathering>","name":"<short name>","regionKey":"<region key>"}],"remove":["<marker id>"]}',
     '}',
     '',
     'HARD CONSTRAINTS',
     '- Use only nation ids and region keys that exist in the provided state.',
     '- A region key identifies one sub-region; the "regions" table in the user message maps each key to "<region name> (<parent country ISO_A3>)". Use those keys in territoryChanges and unowned.',
     '- List in "unowned" only region keys that a nation currently owns, and narrate each release in "events".',
-    '- To rename a nation, add {"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"} to "nationOps". This is a PROPOSAL: it only takes effect if the player confirms it, so use it only when the narrative justifies it (a revolution, reunification, regime change) — at most 1-2 per turn — and narrate it in "events".',
+    '- Map markers ("markers") are named points on the map, anchored to a region key you own or that the narrative justifies: a capital (a nation\'s main seat of power — at most one per nation), major cities, factory complexes, army deployments, ports, fleet concentrations, rocket launch sites, or a gathering (a large political/social mass event that can enable a non-military takeover). Use only region keys from the "regions" table, keep each name under 40 characters, and place at most a handful of new markers per turn — only where the narrative justifies it. List a marker id from the user message\'s "markers" field in "remove" when it ceases to exist (a city razed, an army dispersed, a site destroyed).',
+    '- Nation-management ops ("nationOps") are PROPOSALS: they only take effect if the player confirms them afterwards. Propose at most 1-2 per turn, only when the narrative justifies it, and narrate each one in "events".',
+    '- Rename: add {"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"} for a revolution, regime change or reunification that changes a nation\'s name.',
+    '- Split: add {"kind":"split","nationRef":"<nation id or name>","parts":[{"name":"<new name>","territory":["<region key>"]}, ...]} when a state breaks up (dissolution, secession). Use at least 2 parts and assign each of the nation\'s region keys to at most one part — any key you leave unassigned goes to the first part.',
+    '- Merge: add {"kind":"merge","nationRefs":["<id or name>","<id or name>"],"survivingRef":"<id or name of the surviving nation>","into":"<new name>"} when states reunify or one is absorbed. Use at least 2 input nations and "survivingRef" must name one of them — the survivor keeps its id and its stats.',
     '- Prefer 1-4 events per turn; keep each text 1-3 sentences.',
     '- Keep your internal reasoning brief (a few sentences) and go straight to the JSON result; do not over-deliberate or re-derive facts already present in the state.',
     '- Keep every stat value between 0 and 100.',
@@ -221,6 +242,14 @@ export function buildUserPrompt(
    * Omitted entirely when undefined.
    */
   noMansLand?: string[],
+  /**
+   * (v0.27, #44) The game's current map markers, as the model sees them:
+   * stable id, type, name, region key and current owner. Emitted verbatim
+   * (even when empty) so the model can reference a marker's id in
+   * `TurnResult.markers.remove` or leave an existing marker untouched.
+   * Omitted entirely when undefined.
+   */
+  markers?: MarkerInfo[],
 ): string {
   const player = state.nations[state.playerNationId];
   const playerName = player?.name ?? state.playerNationId;
@@ -259,6 +288,7 @@ export function buildUserPrompt(
   if (regionReference) payload.regions = regionReference;
   if (frontier !== undefined) payload.frontier = frontier;
   if (noMansLand !== undefined) payload.unowned = noMansLand;
+  if (markers !== undefined) payload.markers = markers;
   return JSON.stringify(payload, null, 2);
 }
 
@@ -382,6 +412,7 @@ export function validateTurnResult(input: unknown): TurnResult | null {
     territoryChanges: [],
     unowned: [],
     nationOps: [],
+    markers: { add: [], remove: [] },
   };
 
   if (Array.isArray(o.events)) {
@@ -471,9 +502,51 @@ export function validateTurnResult(input: unknown): TurnResult | null {
   // list for the player to confirm/reject.
   result.nationOps = validateNationOps(o.nationOps);
 
+  // (v0.27, #44) Map-marker ops: new placements (validated here) and
+  // removals by stable id. Applied by applyTurnResult after the territory
+  // moves (a new marker's owner is the region's post-turn owner).
+  result.markers = validateMarkerOps(o.markers);
+
   return result;
 }
 
+/**
+ * (v0.27, #44) Validate the raw `markers` object of a turn into a safe
+ * `{ add, remove }` shape. Defensive like the rest of the parser — never
+ * throws. `add`: each spec needs a known marker type, a non-empty `name`
+ * (capped at 120 chars) and a non-empty `regionKey` (capped at 120 chars);
+ * specs whose derived id collides with an earlier one in the same batch
+ * collapse to the first (re-adding is idempotent). `remove`: deduped,
+ * non-empty marker ids (capped at 120 chars).
+ */
+export function validateMarkerOps(raw: unknown): { add: MarkerSpec[]; remove: string[] } {
+  const out: { add: MarkerSpec[]; remove: string[] } = { add: [], remove: [] };
+  if (!raw || typeof raw !== 'object' || Array.isArray(raw)) return out;
+  const o = raw as Record<string, unknown>;
+  if (Array.isArray(o.add)) {
+    const seen = new Set<string>();
+    for (const e of o.add) {
+      if (!e || typeof e !== 'object') continue;
+      const s = e as Record<string, unknown>;
+      if (!isMarkerType(s.type)) continue;
+      const name = str(s.name, 120);
+      const regionKey = str(s.regionKey, 120);
+      if (!name || !regionKey) continue;
+      const id = markerId(s.type, name, regionKey);
+      if (seen.has(id)) continue;
+      seen.add(id);
+      out.add.push({ type: s.type, name, regionKey });
+    }
+  }
+  if (Array.isArray(o.remove)) {
+    for (const k of o.remove) {
+      const s = typeof k === 'string' ? k.trim() : '';
+      if (s && !out.remove.includes(s)) out.remove.push(s.slice(0, 120));
+    }
+  }
+  return out;
+}
+
 /**
  * A turn is "meaningful" if it produced at least an event, a stat change, a
  * no-man's-land release (v0.22 #16 P3: a release is a real world change even
@@ -487,7 +560,10 @@ export function isMeaningful(result: TurnResult): boolean {
     result.events.length > 0 ||
     result.stateChanges.length > 0 ||
     result.unowned.length > 0 ||
-    result.nationOps.length > 0
+    result.nationOps.length > 0 ||
+    // (v0.27, #44) a marker placed or removed this turn is a real world change.
+    result.markers.add.length > 0 ||
+    result.markers.remove.length > 0
   );
 }
 
@@ -505,15 +581,38 @@ function genericUnclearEvent(state: GameState): TurnEventSpec {
 
 /**
  * Apply a TurnResult to a GameState immutably: advance the date/turn, append
- * events, apply stat changes (clamped), symmetric relations, and territory
- * moves (including no-man's-land releases, v0.22 #16 P3). It also appends any
- * proposed nation-ops to the pending list (v0.23 #16 P4a) without applying
- * them — see the doc comment on `pendingNationOps` for why that list
- * deliberately survives across turns.
+ * events, apply stat changes (clamped), symmetric relations, territory moves
+ * (including no-man's-land releases, v0.22 #16 P3) and map markers (v0.27
+ * #44). It also appends any proposed nation-ops to the pending list (v0.23
+ * #16 P4a) without applying them — see the doc comment on `pendingNationOps`
+ * for why that list deliberately survives across turns.
+ *
+ * `centroidOf` (v0.27, #44) resolves a region key to its precomputed centroid
+ * (`{ lat, lon, spread }`, from public/region-centroids.json via
+ * server/regions.ts). New markers are positioned at that centroid plus a small
+ * deterministic offset; a spec whose key has no known centroid is dropped.
+ * Without it no marker can be placed (all adds are dropped), which keeps the
+ * engine pure and lets tests inject their own data.
+ *
+ * `geoOf` (v0.28, #46) resolves a region key to its area + population
+ * (from public/region-geo.json via server/regions.ts), used to weight the
+ * end-of-turn recompute of each nation's derived stats as the
+ * area×population-weighted median of its regions' stats. Without it the
+ * recompute degrades to an unweighted median (every region weight 1) — still
+ * region-consistent, just unweighted. The engine stays pure either way.
  */
-export function applyTurnResult(state: GameState, result: TurnResult, validKeys?: ReadonlySet<string>): GameState {
+export function applyTurnResult(
+  state: GameState,
+  result: TurnResult,
+  validKeys?: ReadonlySet<string>,
+  centroidOf?: (key: string) => { lat: number; lon: number; spread: number } | undefined,
+  geoOf?: (key: string) => { area: number; population: number } | undefined,
+): GameState {
   const next: GameState = JSON.parse(JSON.stringify(state));
   next.version = (state.version ?? 0) + 1; // every mutation is a new revision
+  // (v0.28, #46) per-region stats table; a legacy/corrupt clone without the
+  // field starts empty (the turn then re-inits claimed regions as it goes).
+  next.regionStats = next.regionStats ?? {};
   const actingTurn = state.turn; // this action resolves the current turn
   next.turn = state.turn + 1; // then we advance to the next turn to play
   next.date = isDateLike(result.date) ? result.date : addDays(state.date, 2);
@@ -522,11 +621,6 @@ export function applyTurnResult(state: GameState, result: TurnResult, validKeys?
   for (const ev of result.events) {
     next.events.push(makeEvent(ev, actingTurn, next.date));
   }
-  for (const c of result.stateChanges) {
-    const n = next.nations[c.nation];
-    if (!n) continue;
-    n.stats[c.stat] = c.op === 'set' ? clampStat(c.value) : clampStat(n.stats[c.stat] + c.value);
-  }
   for (const r of result.relations) {
     const a = next.nations[r.a];
     const b = next.nations[r.b];
@@ -576,6 +670,10 @@ export function applyTurnResult(state: GameState, result: TurnResult, validKeys?
     if (owners.length !== 1) continue; // 0 owners (never assigned) or 2+ (corrupt): no-op
     unowned.add(key);
     next.nations[owners[0]].territory = next.nations[owners[0]].territory.filter((k) => k !== key);
+    // (v0.28, #46) a released region leaves no-man's land ownerless — its
+    // per-region stats leave the table with it (no man's land carries none;
+    // a later re-claim re-inits the entry from the gainer, see below).
+    delete next.regionStats[key];
   }
 
   // (2) Claims against the post-release ownership snapshot.
@@ -622,9 +720,119 @@ export function applyTurnResult(state: GameState, result: TurnResult, validKeys?
     }
     next.nations[gainer].territory.push(key);
     unowned.delete(key); // re-claimed: the key leaves no man's land
+    // (v0.28, #46) a transferred region keeps its own per-region stats (the
+    // conquest is what makes a nation's regions diverge); only a re-claimed
+    // region that has no entry left (it was released earlier this turn) is
+    // re-inited as a copy of the gainer's current stats, so the recompute
+    // below never sees a hole in the table.
+    if (!next.regionStats[key]) next.regionStats[key] = { ...next.nations[gainer].stats };
   }
 
   next.unowned = [...unowned];
+
+  // --- Per-region stats (v0.28, #46): nation-level stateChanges re-applied to
+  //     the regions, then every nation's stats recomputed as the derived
+  //     area×population-weighted median of its regions ---
+  //
+  //  (a) A nation-level stat change (`stateChanges`) is re-interpreted as
+  //      applying to EVERY region the nation owns: each owned region's copy of
+  //      that stat gets the same `set`/`add` (clamped to 0–100), and the
+  //      nation-level stat is updated too (it is kept as-is for nations the
+  //      recompute below does not touch — see (b) — and overwritten for the
+  //      rest, where the regions are the source of truth).
+  //
+  //  (b) RECOMPUTE: every nation's `stats` is re-derived as the weighted
+  //      median of its owned regions' stats (via deriveNationStats, weighted
+  //      by area×population when `geoOf` is available, unweighted otherwise).
+  //      Two guards keep degenerate states sane: a nation with NO regions
+  //      keeps its stats untouched (it has no regions to aggregate), and a
+  //      nation none of whose regions has a stats entry keeps its stats
+  //      too (deriveNationStats would return zeros, which would be wrong).
+  //      This recompute is what makes a conquered region's foreign stats
+  //      blend into the conqueror's aggregate and keeps the derived stats in
+  //      lockstep with the per-region table across the turn's changes.
+  for (const c of result.stateChanges) {
+    const n = next.nations[c.nation];
+    if (!n) continue;
+    for (const key of n.territory) {
+      const rs = next.regionStats[key];
+      if (!rs) continue; // a key with no entry is skipped (recompute does the same)
+      rs[c.stat] = c.op === 'set' ? clampStat(c.value) : clampStat(rs[c.stat] + c.value);
+    }
+    n.stats[c.stat] = c.op === 'set' ? clampStat(c.value) : clampStat(n.stats[c.stat] + c.value);
+  }
+  for (const n of Object.values(next.nations)) {
+    if (n.territory.length === 0) continue; // 0-region guard: no regions to aggregate
+    if (!n.territory.some((k) => next.regionStats[k])) continue; // no entry: keep n.stats
+    n.stats = deriveNationStats(n.territory, next.regionStats, geoOf);
+  }
+
+  // --- Map markers (v0.27, #44) ---
+  //
+  // Markers are anchored to a region key and are processed against the FINAL
+  // post-claim ownership, in this order:
+  //   (1) REMOVE: a marker whose id is in result.markers.remove is dropped
+  //       (a listed-but-absent id is a no-op).
+  //   (2) OWNER RECOMPUTE: every surviving marker's ownerNationId is set to
+  //       its region's current owner — a captured region follows the new
+  //       owner, a region released to no man's land (or a key with 0 or 2+
+  //       owners) becomes `null`. A marker always follows its region.
+  //   (3) ADD: each new spec (in order) is placed at its region's centroid
+  //       (injected via centroidOf) plus a small deterministic per-axis
+  //       offset, owned by the region's post-turn owner, and stamped with
+  //       the acting turn. Dropped (never throws): a region key that is not
+  //       in validKeys or has no known centroid, an id that already exists
+  //       (a re-add is idempotent — the existing marker stays), and any adds
+  //       beyond MAX_MARKERS (the later ones).
+  {
+    const finalOwner = new Map<string, string | null>();
+    {
+      const owners = new Map<string, string[]>();
+      for (const n of Object.values(next.nations)) {
+        for (const key of n.territory) {
+          if (!valid(key)) continue;
+          const list = owners.get(key);
+          if (list) list.push(n.id);
+          else owners.set(key, [n.id]);
+        }
+      }
+      for (const [key, list] of owners) finalOwner.set(key, list.length === 1 ? list[0] : null);
+    }
+    const removeIds = new Set(result.markers.remove);
+    const markers: MapMarker[] = [];
+    for (const m of next.markers ?? []) {
+      if (removeIds.has(m.id)) continue;
+      markers.push({ ...m, ownerNationId: finalOwner.get(m.regionKey) ?? null });
+    }
+    // Deterministic ±(spread/2) offset per axis: a FNV-1a-derived unit
+    // fraction of the marker id (stable across runs and platforms), so
+    // markers of one region scatter naturally instead of stacking.
+    const jitter = (id: string, axis: 'lat' | 'lon', spread: number): number => {
+      const frac = (fnv1a32(`${id}#${axis}`) >>> 8) / 0x00ffffff;
+      return (frac * 2 - 1) * (spread / 2);
+    };
+    const round6 = (v: number): number => Math.round(v * 1e6) / 1e6;
+    for (const spec of result.markers.add) {
+      const id = markerId(spec.type, spec.name, spec.regionKey);
+      if (markers.some((m) => m.id === id)) continue; // re-add: idempotent, keep the existing
+      if (markers.length >= MAX_MARKERS) continue; // hard cap: drop the excess
+      if (!valid(spec.regionKey)) continue; // unknown region key
+      const c = centroidOf?.(spec.regionKey);
+      if (!c) continue; // no centroid data for this key
+      markers.push({
+        id,
+        type: spec.type,
+        name: spec.name,
+        regionKey: spec.regionKey,
+        lat: round6(c.lat + jitter(id, 'lat', c.spread)),
+        lon: round6(c.lon + jitter(id, 'lon', c.spread)),
+        ownerNationId: finalOwner.get(spec.regionKey) ?? null,
+        placedTurn: actingTurn,
+      });
+    }
+    next.markers = markers;
+  }
+
   // (v0.23, #16 P4a) Nation-op proposals are NOT applied by the turn — they
   // are appended to the pending list, which (unlike `pending`) SURVIVES
   // across turns until the player confirms or rejects each one. `next` is a
@@ -700,39 +908,208 @@ export function resolveNationRef(state: GameState, ref: string): string | null {
   return matches.length === 1 ? matches[0].id : null;
 }
 
+/**
+ * Generate a fresh, unused nation id for a newly created nation (split
+ * parts, v0.24 #16 P4b): the first free of `n1`, `n2`, ... The caller adds
+ * each id it creates to `taken` as it goes, so ids stay unique within an
+ * op and are never reused from a removed nation.
+ */
+export function freshNationId(taken: ReadonlySet<string>): string {
+  for (let i = 1; ; i++) {
+    const id = `n${i}`;
+    if (!taken.has(id)) return id;
+  }
+}
+
+/**
+ * The baseline stats a freshly created nation starts with (split parts,
+ * v0.24 #16 P4b) — a neutral middle-of-the-scale profile, deliberately NOT
+ * a copy of the parent's stats (a small rump state is not the parent's
+ * military power).
+ */
+export const NEW_NATION_STATS: NationStats = {
+  military: 50,
+  economy: 50,
+  stability: 50,
+  population: 50,
+};
+
+/**
+ * Defensive cleanup after nations are removed (merge, v0.24 #16 P4b): drop
+ * the removed nations' ids from every remaining nation's `relations` map so
+ * no key dangles. (The client already degrades gracefully on a missing
+ * target, but consistent data is cleaner.)
+ */
+function dropRelationsTo(state: GameState, removedIds: ReadonlySet<string>): void {
+  for (const n of Object.values(state.nations)) {
+    for (const id of removedIds) {
+      if (id in n.relations) delete n.relations[id];
+    }
+  }
+}
+
 /**
  * Apply one NationOp to a state, MUTATING the passed object in place (the
  * caller passes a clone — confirmNationOp does) and NOT bumping `version`
- * (the route-level functions do that once per decision). Rename changes only
- * `Nation.name` — the id, its territory, its relations (keyed by id), and the
- * player pointer all stay valid, so nothing downstream breaks; a
- * player-supplied `edits.name` overrides the proposed `to` (an empty edit
- * falls back to the proposal's own name). An unresolvable or ambiguous
- * `nationRef` is a silent no-op. Split and merge are declared for P4b and are
- * a no-op until then — the op stays pending-free once the player resolves it,
- * but the world does not change yet.
+ * (the route-level functions do that once per decision). It never throws:
+ * any unresolvable reference or malformed op is a silent no-op (the op is
+ * still removed by confirmNationOp — the world simply doesn't change).
+ *
+ *  - **rename** (v0.23, #16 P4a): changes only `Nation.name` — the id, its
+ *    territory, its relations (keyed by id), and the player pointer all stay
+ *    valid, so nothing downstream breaks; a player-supplied `edits.name`
+ *    overrides the proposed `to` (an empty edit falls back to the proposal's
+ *    own name).
+ *
+ *  - **split** (v0.24, #16 P4b): the `nationRef` must resolve and there must
+ *    be at least two named parts, else no-op. Parts are processed in order;
+ *    each receives the region keys of its `territory` that (a) the parent
+ *    owns and (b) no earlier part claimed — the first part to name a key
+ *    wins. Keys of the parent's territory that no part claimed go to part 0
+ *    (in the parent's `territory` order), so the parent's territory is fully
+ *    partitioned — no key is lost or ever held twice. Each part gets a
+ *    FRESH id (`freshNationId`) and the baseline `NEW_NATION_STATS` (not a
+ *    copy of the parent's), plus a copy of the parent's relations; the
+ *    parent is then removed. If the parent was the player's nation,
+ *    `playerNationId` moves to the chosen part (`edits.playerPart`, clamped
+ *    into range, default 0); `edits.name` renames that same chosen part.
+ *
+ *  - **merge** (v0.24, #16 P4b): every input ref plus the survivor ref must
+ *    resolve, at least two inputs must resolve to DISTINCT nations, and the
+ *    survivor must be one of them — else no-op. The survivor keeps its id,
+ *    keeps its own stats, gains the union of all inputs' territories
+ *    (survivor's keys first, then each other input's unclaimed keys in its
+ *    own order), and gains a union of the inputs' relations (on a third
+ *    party the survivor's own view wins, else the first input's). The other
+ *    inputs are removed (their ids dropped from everyone else's relations
+ *    maps), and if the player led a removed input, `playerNationId` moves to
+ *    the survivor. The merged name is `edits.name` (if non-empty), else
+ *    `op.into`, else the survivor's current name.
  */
-export function applyNationOp(state: GameState, op: NationOp, edits?: { name?: string }): void {
-  if (op.kind !== 'rename') return; // split/merge: declared for P4b, not applied yet
-  const id = resolveNationRef(state, op.nationRef);
-  if (id === null) return; // invalid/ambiguous ref: no-op
-  const n = state.nations[id];
-  if (!n) return;
-  const name = (edits?.name ?? '').trim() || op.to.trim();
-  if (name) n.name = name;
+export function applyNationOp(
+  state: GameState,
+  op: NationOp,
+  edits?: { name?: string; playerPart?: number },
+): void {
+  if (op.kind === 'rename') {
+    const id = resolveNationRef(state, op.nationRef);
+    if (id === null) return; // invalid/ambiguous ref: no-op
+    const n = state.nations[id];
+    if (!n) return;
+    const name = (edits?.name ?? '').trim() || op.to.trim();
+    if (name) n.name = name;
+    return;
+  }
+
+  if (op.kind === 'split') {
+    const id = resolveNationRef(state, op.nationRef);
+    if (id === null || op.parts.length < 2) return; // invalid ref / not enough parts: no-op
+    const parent = state.nations[id];
+    if (!parent) return;
+    const taken = new Set(Object.keys(state.nations));
+    const created: string[] = [];
+    const claimed = new Set<string>();
+    for (const part of op.parts) {
+      const newId = freshNationId(taken);
+      taken.add(newId);
+      const keys = (part.territory ?? [])
+        .filter((k) => parent.territory.includes(k) && !claimed.has(k));
+      for (const k of keys) claimed.add(k);
+      const partNation: Nation = {
+        id: newId,
+        type: parent.type, // a part keeps the parent's form of state
+        name: part.name,
+        stats: { ...NEW_NATION_STATS },
+        territory: keys,
+        relations: { ...parent.relations },
+      };
+      state.nations[newId] = partNation;
+      created.push(newId);
+    }
+    // Keys the parent owned but no part claimed go to part 0 (in the
+    // parent's territory order) — nothing is lost or duplicated.
+    for (const k of parent.territory) {
+      if (!claimed.has(k)) state.nations[created[0]].territory.push(k);
+    }
+    // The player chooses which part is its successor (edits.playerPart,
+    // clamped into range; default 0) — only relevant when the parent was
+    // the player's nation; the same part also gets a player-edited name.
+    const partIdx =
+      Math.min(Math.max(edits?.playerPart ?? 0, 0), created.length - 1);
+    if (state.playerNationId === id) state.playerNationId = created[partIdx];
+    const editedName = (edits?.name ?? '').trim();
+    if (editedName) state.nations[created[partIdx]].name = editedName;
+    delete state.nations[id];
+    dropRelationsTo(state, new Set([id]));
+    return;
+  }
+
+  // merge
+  const resolved: string[] = [];
+  for (const ref of op.nationRefs) {
+    const rid = resolveNationRef(state, ref);
+    if (rid === null) return; // any unresolvable input: no-op
+    resolved.push(rid);
+  }
+  const inputIds = new Set(resolved);
+  const survivorId = resolveNationRef(state, op.survivingRef);
+  if (survivorId === null || !inputIds.has(survivorId) || inputIds.size < 2) return;
+  const survivor = state.nations[survivorId];
+  if (!survivor) return;
+  // Territory: the union of all inputs — the survivor's keys first (stable
+  // order), then each other input's unclaimed keys in its own order.
+  const territory = [...survivor.territory];
+  const seen = new Set(territory);
+  for (const rid of resolved) {
+    for (const k of state.nations[rid].territory) {
+      if (!seen.has(k)) {
+        seen.add(k);
+        territory.push(k);
+      }
+    }
+  }
+  // Relations: the union of all inputs' relations; the first input to name a
+  // third party sets it, then the survivor's own view overwrites per key.
+  const relations: Record<string, RelationStatus> = {};
+  for (const rid of resolved) {
+    for (const [other, status] of Object.entries(state.nations[rid].relations)) {
+      if (other === survivorId) continue; // never relate to oneself
+      if (!(other in relations)) relations[other] = status;
+    }
+  }
+  for (const [other, status] of Object.entries(survivor.relations)) {
+    if (other !== survivorId) relations[other] = status;
+  }
+  const removed = new Set<string>();
+  for (const rid of inputIds) {
+    if (rid === survivorId) continue;
+    delete state.nations[rid];
+    removed.add(rid);
+  }
+  if (state.playerNationId !== survivorId && removed.has(state.playerNationId)) {
+    state.playerNationId = survivorId;
+  }
+  const name = (edits?.name ?? '').trim() || op.into.trim() || survivor.name;
+  if (name) survivor.name = name;
+  survivor.territory = territory;
+  survivor.relations = relations;
+  dropRelationsTo(state, removed);
 }
 
 /**
  * Confirm a pending nation-op proposal by index: apply it (a rename takes
- * effect, optionally with a player-edited name; split/merge are a no-op until
- * P4b) and remove it from `pendingNationOps`, bumping `version`. Returns
- * `null` for an invalid index, so the route answers 400 without mutating.
- * Reused by the /nation-op/confirm route.
+ * effect, optionally with a player-edited name; a split partitions the
+ * nation's territory into the new parts, the player picking which part is
+ * its successor via `edits.playerPart`; a merge folds the inputs into the
+ * survivor, optionally renamed via `edits.name`) and remove it from
+ * `pendingNationOps`, bumping `version`. Returns `null` for an invalid
+ * index, so the route answers 400 without mutating. Reused by the
+ * /nation-op/confirm route.
  */
 export function confirmNationOp(
   state: GameState,
   index: number,
-  edits?: { name?: string },
+  edits?: { name?: string; playerPart?: number },
 ): GameState | null {
   if (!validPendingOpIndex(state, index)) return null;
   const next: GameState = JSON.parse(JSON.stringify(state));
@@ -785,15 +1162,39 @@ export async function runTurn(opts: {
    * switches the turn onto the getNeighbours tool path.
    */
   getNeighbours?: (keys: string[]) => string[];
+  /**
+   * (v0.27, #44) Region-key -> precomputed centroid resolver (from
+   * public/region-centroids.json). Present, the turn's new markers can be
+   * placed at their region's centroid; absent, marker adds are dropped and
+   * the existing markers' owners still get recomputed.
+   */
+  centroidOf?: (key: string) => { lat: number; lon: number; spread: number } | undefined;
+  /**
+   * (v0.28, #46) Region-key -> area/population resolver (from
+   * public/region-geo.json). Present, the end-of-turn recompute of each
+   * nation's derived stats weights each owned region by area×population;
+   * absent, the recompute degrades to an unweighted (uniform) median —
+   * still region-consistent, just unweighted.
+   */
+  geoOf?: (key: string) => { area: number; population: number } | undefined;
 }): Promise<{ state: GameState; result: TurnResult }> {
-  const { llm, preset, state, items, regionReference, validRegionKeys, getNeighbours } = opts;
+  const { llm, preset, state, items, regionReference, validRegionKeys, getNeighbours, centroidOf, geoOf } = opts;
   const chatWithTools = llm.chatWithTools;
   const useTools = getNeighbours !== undefined && chatWithTools !== undefined;
   const system = buildSystemPrompt(preset, useTools);
   const frontier = getNeighbours ? playerFrontier(state, getNeighbours) : undefined;
   // (v0.22, #16 P3) the model always sees the current no-man's-land keys (empty
   // list on a fresh game) so it knows which unowned regions can be re-claimed.
-  const user = buildUserPrompt(state, items, regionReference, frontier, state.unowned ?? []);
+  // (v0.27, #44) likewise the current map markers, so it can reference their
+  // stable ids in `markers.remove` (or leave them untouched).
+  const markers = (state.markers ?? []).map((m) => ({
+    id: m.id,
+    type: m.type,
+    name: m.name,
+    regionKey: m.regionKey,
+    owner: m.ownerNationId,
+  }));
+  const user = buildUserPrompt(state, items, regionReference, frontier, state.unowned ?? [], markers);
   const nudge =
     'Your previous output was invalid. Respond with ONLY the JSON object described above for this batch — no prose, no fences.';
 
@@ -838,10 +1239,11 @@ export async function runTurn(opts: {
       territoryChanges: [],
       unowned: [],
       nationOps: [],
+      markers: { add: [], remove: [] },
     };
   }
 
-  return { state: applyTurnResult(state, result, validRegionKeys), result };
+  return { state: applyTurnResult(state, result, validRegionKeys, centroidOf, geoOf), result };
 }
 
 // --- Advisor (brainstorm) -----------------------------------------------------

server/index.ts

@@ -8,7 +8,7 @@ import { existsSync } from 'node:fs';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 
-import { deepClone } from '../shared/protocol';
+import { deepClone, seedRegionStats } from '../shared/protocol';
 import type {
   AddActionRequest,
   AddDiplomacyRequest,
@@ -22,7 +22,7 @@ import { createLlmClient } from './llm';
 import { makeStubLlmClient } from './stub';
 import { askAdvisor, confirmNationOp, queueRoundItem, rejectNationOp, removeRoundItem, runTurn } from './engine';
 import { buildRegionMap } from './map';
-import { allTerritoryKeys, expandCountriesToKeys, hasAdjacency, loadRegions, neighboursOf, referenceForKeys, validKeys } from './regions';
+import { allTerritoryKeys, centroidOf, expandCountriesToKeys, geoOf, hasAdjacency, hasCentroids, hasGeo, loadRegions, neighboursOf, referenceForKeys, validKeys } from './regions';
 import { createPresetStore } from './presets';
 import { openDb, type Db } from './db';
 
@@ -134,11 +134,20 @@ app.post('/api/games', (req: Request, res) => {
     // list grows as the LLM proposes renames (and, later, splits/merges) and
     // shrinks as the player confirms or rejects them.
     pendingNationOps: [],
+    // (v0.27, #44) No markers on a fresh game; the LLM places them over time.
+    markers: [],
+    // (v0.28, #46) Per-region stats are seeded below, once territories hold
+    // real region keys — each region starts as a copy of its owner's initial
+    // stats, so the derived aggregate equals the nation's stats on turn 1.
+    regionStats: {},
   };
   // v0.19 (#16 P1): expand each nation's ISO_A3 country list to the region keys
   // of all its sub-regions, so ownership (and the choropleth) is at region
   // granularity from the very first turn. Preset JSONs stay country-level.
   for (const n of Object.values(state.nations)) n.territory = expandCountriesToKeys(n.territory);
+  // (v0.28, #46): seed per-region stats AFTER the expansion so each owned
+  // region key gets its owner's initial stats (see seedRegionStats).
+  state.regionStats = seedRegionStats(state.nations);
   db.save(state);
   res.json({ game: state });
 });
@@ -230,10 +239,14 @@ app.post('/api/games/:id/queue/remove', (req, res) => {
   res.json({ game: next });
 });
 
-// (v0.23, #16 P4a) Resolve a pending nation-op proposal (a rename the LLM
-// proposed in an earlier turn, waiting in game.pendingNationOps). No LLM call,
-// no turn advance — same fast save → broadcast → respond order as
-// /queue/remove. The version bump lets "never go backwards" clients reconcile.
+// (v0.23, #16 P4a; v0.24, #16 P4b) Resolve a pending nation-op proposal
+// waiting in game.pendingNationOps: a rename takes effect (body.edits.name
+// may override the proposed name), a split partitions the nation's territory
+// into the proposed parts (body.edits.playerPart picks which part the player
+// leads, default 0), and a merge folds its inputs into the survivor
+// (body.edits.name may override the merged name). No LLM call, no turn
+// advance — same fast save → broadcast → respond order as /queue/remove.
+// The version bump lets "never go backwards" clients reconcile.
 app.post('/api/games/:id/nation-op/confirm', (req, res) => {
   const id = req.params.id;
   const game = db.load(id);
@@ -284,6 +297,16 @@ app.post('/api/games/:id/jump', async (req, res) => {
       // engine the resolver — the turn then runs with the LLM's getNeighbours
       // tool and the player-frontier prompt field (both switch off without it).
       getNeighbours: hasAdjacency() ? (keys) => neighboursOf(keys) : undefined,
+      // (v0.27, #44) when the centroid manifest loaded, hand the engine the
+      // resolver so a turn can place new map markers at their region's
+      // centroid (without it, marker adds are dropped; existing markers are
+      // still maintained).
+      centroidOf: hasCentroids() ? (key) => centroidOf(key) : undefined,
+      // (v0.28, #46) when the region-geo manifest (area + population) loaded,
+      // hand the engine the resolver so the end-of-turn recompute weights each
+      // owned region by area×population (without it the aggregate degrades to
+      // an unweighted median — still region-consistent, just unweighted).
+      geoOf: hasGeo() ? (key) => geoOf(key) : undefined,
     });
     db.save(state);
     broadcast(id, 'turn', { state, result });

server/map.test.ts

@@ -49,6 +49,9 @@ const state: GameState = {
   version: 1,
   unowned: [],
   pendingNationOps: [],
+  markers: [],
+  // (v0.28, #46) the map is ownership-only; the region-stats table is unused here.
+  regionStats: {},
 };
 
 // The RegionMap built from the fixture: the authoritative region key → owner source.

server/protocol.test.ts

@@ -0,0 +1,220 @@
+import { describe, expect, it } from 'vitest';
+import {
+  deriveNationStats,
+  migrateRegionStats,
+  seedRegionStats,
+  weightedMedian,
+} from '../shared/protocol';
+import type { GameState, Nation, NationStats } from '../shared/types';
+
+// --- Test fixtures -----------------------------------------------------------
+
+const S = (military: number, economy: number, stability: number, population: number): NationStats => ({
+  military,
+  economy,
+  stability,
+  population,
+});
+
+function nation(id: string, name: string, stats: NationStats, territory: string[]): Nation {
+  return { id, name, type: 'major', stats, territory, relations: {} };
+}
+
+function mkState(
+  nations: Record<string, Nation>,
+  regionStats?: Record<string, unknown>,
+): GameState {
+  const base: GameState = {
+    id: 'g',
+    presetId: 'p',
+    presetTitle: 'P',
+    playerNationId: Object.keys(nations)[0] ?? '',
+    turn: 1,
+    date: '1939-09-01',
+    nations,
+    events: [],
+    pending: [],
+    version: 1,
+    unowned: [],
+    pendingNationOps: [],
+    markers: [],
+    regionStats: {} as GameState['regionStats'],
+  };
+  if (regionStats !== undefined) base.regionStats = regionStats as GameState['regionStats'];
+  else delete (base as { regionStats?: unknown }).regionStats; // simulate a legacy row
+  return base;
+}
+
+// --- weightedMedian ----------------------------------------------------------
+
+describe('weightedMedian', () => {
+  it('returns 0 for an empty input or zero total weight', () => {
+    expect(weightedMedian([], [])).toBe(0);
+    expect(weightedMedian([5, 6], [0, 0])).toBe(0); // zero weights
+    expect(weightedMedian([5, 6], [NaN, -1])).toBe(0); // non-finite / non-positive → 0
+  });
+
+  it('returns the single value when it is the only weighted input', () => {
+    expect(weightedMedian([42], [7])).toBe(42);
+  });
+
+  it('the median of a set of IDENTICAL values is that value (translation-invariant)', () => {
+    // The invariant seeding + legacy migration rely on: equal values → that value,
+    // regardless of the (arbitrary) weights.
+    expect(weightedMedian([7, 7, 7], [1, 5, 9])).toBe(7);
+    expect(weightedMedian([0, 0], [10, 20])).toBe(0);
+    expect(weightedMedian([100, 100, 100], [1, 1, 1000])).toBe(100);
+    // and a constant shift shifts the result by the same constant
+    expect(weightedMedian([107, 107, 107], [1, 5, 9])).toBe(weightedMedian([7, 7, 7], [1, 5, 9]) + 100);
+  });
+
+  it('picks the value at the first point the cumulative weight reaches half the total', () => {
+    // two equal weights: the lower value is reached first (cum 1 of 2 ≥ 1)
+    expect(weightedMedian([10, 20], [1, 1])).toBe(10);
+    // an odd middle: the true middle value
+    expect(weightedMedian([10, 20, 30], [1, 1, 1])).toBe(20);
+    // the heavier value dominates
+    expect(weightedMedian([10, 20], [1, 3])).toBe(20);
+    expect(weightedMedian([10, 20], [3, 1])).toBe(10);
+  });
+
+  it('treats non-finite or non-positive weights as excluded (0)', () => {
+    // NaN weight on 10, positive on 20 → only 20 counts
+    expect(weightedMedian([10, 20], [NaN, 1])).toBe(20);
+    // negative weight on 20, positive on 10 → only 10 counts
+    expect(weightedMedian([10, 20], [1, -5])).toBe(10);
+  });
+});
+
+// --- deriveNationStats -------------------------------------------------------
+
+describe('deriveNationStats', () => {
+  const regionStats = {
+    a: S(50, 50, 50, 50),
+    b: S(90, 90, 90, 90),
+  };
+  const geo: Record<string, { area: number; population: number }> = { a: { area: 100, population: 1000 }, b: { area: 1000, population: 1000 } };
+
+  it('weights by area×population: the larger region dominates the aggregate', () => {
+    // a: weight 100×1000=100000, b: weight 1000×1000=1000000 → b (90) dominates
+    const out = deriveNationStats(['a', 'b'], regionStats, (k) => geo[k]);
+    expect(out).toEqual(S(90, 90, 90, 90));
+  });
+
+  it('degrades to a uniform (unweighted) median without geo: the lower value is reached first', () => {
+    // equal weights 1,1 → the lower (a=50) is reached at half-total first
+    const out = deriveNationStats(['a', 'b'], regionStats);
+    expect(out).toEqual(S(50, 50, 50, 50));
+    // same when geoOf is provided but returns undefined for the keys (missing geo)
+    const out2 = deriveNationStats(['a', 'b'], regionStats, () => undefined);
+    expect(out2).toEqual(S(50, 50, 50, 50));
+  });
+
+  it('skips a region key that has no stats entry', () => {
+    // b has no entry → only a is counted → a's (50) values
+    const out = deriveNationStats(['a', 'b'], { a: S(50, 50, 50, 50) }, (k) => geo[k]);
+    expect(out).toEqual(S(50, 50, 50, 50));
+  });
+
+  it('returns zero stats when none of the owned regions has a stats entry', () => {
+    const out = deriveNationStats(['a', 'b'], {}, (k) => geo[k]);
+    expect(out).toEqual(S(0, 0, 0, 0));
+  });
+
+  it('a single region yields exactly that region\'s stats (the seeding invariant)', () => {
+    expect(deriveNationStats(['a'], regionStats, (k) => geo[k])).toEqual(S(50, 50, 50, 50));
+    expect(deriveNationStats(['a'], regionStats)).toEqual(S(50, 50, 50, 50));
+  });
+
+  it('treats zero/negative area or population as a fallback weight of 1', () => {
+    // a has area 0 (weight falls back to 1×pop), b has full weight → b dominates
+    const g: Record<string, { area: number; population: number }> = { a: { area: 0, population: 1000 }, b: { area: 1000, population: 1000 } };
+    const out = deriveNationStats(['a', 'b'], regionStats, (k) => g[k]);
+    expect(out).toEqual(S(90, 90, 90, 90));
+  });
+});
+
+// --- seedRegionStats ---------------------------------------------------------
+
+describe('seedRegionStats', () => {
+  it('copies each owner\'s stats to every region it owns', () => {
+    const nations = {
+      uk: nation('uk', 'UK', S(80, 70, 60, 50), ['k1', 'k2']),
+      de: nation('de', 'DE', S(95, 70, 75, 90), ['k3']),
+    };
+    expect(seedRegionStats(nations)).toEqual({
+      k1: S(80, 70, 60, 50),
+      k2: S(80, 70, 60, 50),
+      k3: S(95, 70, 75, 90),
+    });
+  });
+
+  it('gives the first owner\'s stats a key owned by two or more nations (corrupt)', () => {
+    const nations = {
+      a: nation('a', 'A', S(10, 10, 10, 10), ['k1']),
+      b: nation('b', 'B', S(90, 90, 90, 90), ['k1']),
+    };
+    expect(seedRegionStats(nations)).toEqual({ k1: S(10, 10, 10, 10) });
+  });
+
+  it('returns an empty table for nations with no territory', () => {
+    const nations = { a: nation('a', 'A', S(10, 10, 10, 10), []) };
+    expect(seedRegionStats(nations)).toEqual({});
+  });
+});
+
+// --- migrateRegionStats ------------------------------------------------------
+
+describe('migrateRegionStats', () => {
+  it('returns a v0.28+ row (regionStats present) UNCHANGED — same reference, no recompute', () => {
+    const state = mkState(
+      { uk: nation('uk', 'UK', S(42, 70, 60, 50), ['k1']) },
+      { k1: S(99, 70, 60, 50) }, // deliberately divergent from the nation stats
+    );
+    const out = migrateRegionStats(state);
+    expect(out).toBe(state); // same reference: untouched
+    expect(out.regionStats).toEqual({ k1: S(99, 70, 60, 50) });
+    expect(out.nations.uk.stats).toEqual(S(42, 70, 60, 50)); // NOT recomputed from the region
+  });
+
+  it('migrates a legacy row (regionStats absent): seeds each owned region and preserves stats', () => {
+    const state = mkState({
+      uk: nation('uk', 'UK', S(80, 70, 60, 50), ['k1', 'k2', 'k3']),
+      de: nation('de', 'DE', S(95, 70, 75, 90), ['k4']),
+    });
+    // sanity: we built a legacy row
+    expect((state as { regionStats?: unknown }).regionStats).toBeUndefined();
+
+    const out = migrateRegionStats(state, (k) =>
+      k === 'k1' ? { area: 100, population: 1000 }
+      : k === 'k2' ? { area: 1, population: 1 }
+      : k === 'k3' ? { area: 9, population: 9 }
+      : { area: 50, population: 500 });
+    // each owned region is seeded with a copy of its owner's stats…
+    expect(out.regionStats).toEqual({
+      k1: S(80, 70, 60, 50),
+      k2: S(80, 70, 60, 50),
+      k3: S(80, 70, 60, 50),
+      k4: S(95, 70, 75, 90),
+    });
+    // …and the (multi-region) nation's stats are PRESERVED: the weighted median of
+    // identical values is that value, regardless of the (uneven) weights.
+    expect(out.nations.uk.stats).toEqual(S(80, 70, 60, 50));
+    expect(out.nations.de.stats).toEqual(S(95, 70, 75, 90));
+    // the original row is NOT mutated
+    expect((state as { regionStats?: unknown }).regionStats).toBeUndefined();
+    expect(state.nations.uk.stats).toEqual(S(80, 70, 60, 50));
+  });
+
+  it('a legacy 0-region nation keeps its stats (no recompute, no entries)', () => {
+    const state = mkState({
+      uk: nation('uk', 'UK', S(80, 70, 60, 50), []),
+      de: nation('de', 'DE', S(95, 70, 75, 90), ['k1']),
+    });
+    const out = migrateRegionStats(state);
+    expect(out.nations.uk.stats).toEqual(S(80, 70, 60, 50)); // unchanged
+    expect(out.nations.de.stats).toEqual(S(95, 70, 75, 90)); // single region → preserved
+    expect(out.regionStats).toEqual({ k1: S(95, 70, 75, 90) });
+    expect('uk' in (out.regionStats ?? {})).toBe(false);
+  });
+});

server/regions.test.ts

@@ -5,8 +5,12 @@ import { tmpdir } from 'node:os';
 import path from 'node:path';
 import {
   allTerritoryKeys,
+  centroidOf,
   expandCountriesToKeys,
+  geoOf,
   hasAdjacency,
+  hasCentroids,
+  hasGeo,
   hasRegionData,
   loadRegions,
   neighboursOf,
@@ -27,9 +31,9 @@ describe('regions (region-key loader, v0.19 #16 P1)', () => {
     expect(loadRegions(root)).toBe(true);
   });
 
-  it('loads the full manifest: 1,796 unique valid region keys', () => {
+  it('loads the full manifest: 1,800 unique valid region keys', () => {
     expect(hasRegionData()).toBe(true);
-    expect(validKeys().size).toBe(1796);
+    expect(validKeys().size).toBe(1800);
   });
 
   it('expands an ISO_A3 country to the region keys of all its sub-regions', () => {
@@ -51,6 +55,21 @@ describe('regions (region-key loader, v0.19 #16 P1)', () => {
     expect(ref['aisne-gstu']).toBe('Aisne (FRA)');
   });
 
+  it('expands RUS to all 84 sub-regions after the #31 + #41 Arkhangel splits (no ownership gap at game init)', () => {
+    // #31 split RU-ARK into the mainland + New Earth + Severnaya Zemlya; #41
+    // repartitioned the mainland into the core (unchanged key) + Pechora +
+    // Yamal. A fresh game's RUS territory (expanded from the preset's
+    // country list) must contain all five sub-region keys — the main one
+    // (ownership-safe, unchanged key) plus the island and band ones.
+    const rus = expandCountriesToKeys(['RUS']);
+    expect(rus).toHaveLength(84);
+    expect(rus).toContain('arkhangel-sk-lhbk');
+    expect(rus).toContain('new-earth-eikt');
+    expect(rus).toContain('severnaya-zemlya-awqp');
+    expect(rus).toContain('pechora-qwhs');
+    expect(rus).toContain('yamal-gosw');
+  });
+
   it('referenceForKeys labels only known keys and omits unknown ones', () => {
     const ref = referenceForKeys(['ain-lqtt', 'not-a-real-key-xyz']);
     expect(ref['ain-lqtt']).toBe('Ain (FRA)');
@@ -88,6 +107,9 @@ describe('regions (region-key loader, v0.19 #16 P1)', () => {
       version: 1,
       unowned: [],
       pendingNationOps: [],
+      markers: [],
+      // (v0.28, #46) unused here (allTerritoryKeys is ownership-only).
+      regionStats: {},
     };
     // 16 GBR sub-regions + 42 FRA sub-regions, no overlap between the two.
     expect(allTerritoryKeys(state).size).toBe(58);
@@ -118,6 +140,34 @@ describe('regions (region-key loader, v0.19 #16 P1)', () => {
     expect(neighboursOf([])).toEqual([]);
   });
 
+  it('(v0.27 #44) hasCentroids() is true and centroidOf resolves a real key to a plausible location', () => {
+    expect(hasCentroids()).toBe(true);
+    const ain = centroidOf('ain-lqtt');
+    expect(ain).toBeDefined();
+    expect(ain!.lat).toBeCloseTo(46.16, 1);
+    expect(ain!.lon).toBeCloseTo(4.8, 1);
+    expect(ain!.spread).toBeGreaterThan(0);
+  });
+
+  it('(v0.27 #44) centroidOf returns undefined for an unknown key', () => {
+    expect(centroidOf('not-a-real-key-xyz')).toBeUndefined();
+  });
+
+  it('(v0.28 #46) hasGeo() is true and geoOf resolves a real key to area + population', () => {
+    expect(hasGeo()).toBe(true);
+    const ain = geoOf('ain-lqtt');
+    expect(ain).toBeDefined();
+    expect(ain!.area).toBeGreaterThanOrEqual(0); // km²
+    expect(ain!.population).toBeGreaterThanOrEqual(0);
+    // exact spot-check values pinned from the committed manifest (Ain, FRA)
+    expect(ain!.area).toBeCloseTo(22557.77, 1); // km²
+    expect(ain!.population).toBe(2304126);
+  });
+
+  it('(v0.28 #46) geoOf returns undefined for an unknown key', () => {
+    expect(geoOf('not-a-real-key-xyz')).toBeUndefined();
+  });
+
   describe('graceful degradation with no region data', () => {
     beforeEach(() => resetRegions());
 
@@ -131,6 +181,12 @@ describe('regions (region-key loader, v0.19 #16 P1)', () => {
       // and no adjacency: the LLM tool / frontier field switch off
       expect(hasAdjacency()).toBe(false);
       expect(neighboursOf(['moselle-rygy'])).toEqual([]);
+      // and no centroids: the marker-placement path degrades to a no-op
+      expect(hasCentroids()).toBe(false);
+      expect(centroidOf('ain-lqtt')).toBeUndefined();
+      // and no region-geo: the per-region stats weighting degrades to uniform
+      expect(hasGeo()).toBe(false);
+      expect(geoOf('ain-lqtt')).toBeUndefined();
     });
   });
 
@@ -166,13 +222,13 @@ describe('loadRegions resolves the manifest per environment (dev public/ vs prod
   it('loads from dist/ when public/ is absent (the prod container layout)', () => {
     expect(loadRegions(prodRoot)).toBe(true);
     expect(hasRegionData()).toBe(true);
-    expect(validKeys().size).toBe(1796);
+    expect(validKeys().size).toBe(1800);
     expect(expandCountriesToKeys(['FRA'])).toHaveLength(42);
   });
 
   it('still loads from public/ (the dev layout, the first candidate)', () => {
     expect(loadRegions(realRoot)).toBe(true);
-    expect(validKeys().size).toBe(1796);
+    expect(validKeys().size).toBe(1800);
   });
 
   it('a dist/ WITHOUT the adjacency manifest degrades: hasAdjacency() false, neighboursOf []', () => {
@@ -182,6 +238,37 @@ describe('loadRegions resolves the manifest per environment (dev public/ vs prod
     expect(loadRegions(prodRoot)).toBe(true);
     expect(hasAdjacency()).toBe(false);
     expect(neighboursOf(['moselle-rygy'])).toEqual([]);
+    // and no centroids (not copied into this dist/) -> marker placement degrades
+    expect(hasCentroids()).toBe(false);
+    expect(centroidOf('ain-lqtt')).toBeUndefined();
+    // and no region-geo (not copied into this dist/) -> stats weighting is uniform
+    expect(hasGeo()).toBe(false);
+    expect(geoOf('ain-lqtt')).toBeUndefined();
+  });
+
+  it('(v0.27 #44) a dist/ WITH the centroids manifest loads them (prod layout)', () => {
+    copyFileSync(
+      path.join(realRoot, 'public', 'region-centroids.json'),
+      path.join(prodRoot, 'dist', 'region-centroids.json'),
+    );
+    expect(loadRegions(prodRoot)).toBe(true);
+    expect(hasCentroids()).toBe(true);
+    const ain = centroidOf('ain-lqtt');
+    expect(ain).toBeDefined();
+    expect(ain!.lat).toBeCloseTo(46.16, 1);
+  });
+
+  it('(v0.28 #46) a dist/ WITH the region-geo manifest loads it (prod layout)', () => {
+    copyFileSync(
+      path.join(realRoot, 'public', 'region-geo.json'),
+      path.join(prodRoot, 'dist', 'region-geo.json'),
+    );
+    expect(loadRegions(prodRoot)).toBe(true);
+    expect(hasGeo()).toBe(true);
+    const ain = geoOf('ain-lqtt');
+    expect(ain).toBeDefined();
+    expect(ain!.area).toBeCloseTo(22557.77, 1);
+    expect(ain!.population).toBe(2304126);
   });
 
   it('returns false and no data when neither public/ nor dist/ holds the files', () => {

server/regions.ts

@@ -2,7 +2,9 @@
 // (region-keys.json: stable feature id -> region key), the sub-national geo
 // (regions.geo.json: feature id -> { name, parent }), and — optionally — the
 // precomputed region-adjacency manifest (region-adjacency.json: region key ->
-// bordering region keys, built by scripts/build-region-adjacency.mjs) — all
+// bordering region keys, built by scripts/build-region-adjacency.mjs) and the
+// precomputed region-centroid manifest (region-centroids.json: region key ->
+// { lat, lon, spread }, built by scripts/build-region-centroids.mjs) — all
 // from public/ in dev (Vite serves it) or dist/ in prod (Vite copies
 // public/* -> dist/ at build, and the Docker image keeps only dist/) — and
 // joins them into the lookups the region-level ownership model needs:
@@ -13,6 +15,10 @@
 //   - neighboursOf(): the union of the bordering keys for a set of keys — the
 //     data behind the LLM's getNeighbours tool and the player-frontier prompt
 //     field (v0.21, #16 P2)
+//   - centroidOf(): a region key's precomputed anchor point ({ lat, lon, spread })
+//     — the data behind LLM-placed map markers (v0.27, #44)
+//   - geoOf(): a region key's area (km²) + population (from region-geo.json)
+//     — the weighting source for the per-region stats model (v0.28, #46)
 //
 // Deliberately turf-free: it reads the JSON files with plain JSON.parse and
 // never imports @turf/@types/geojson (importing one pulls @types/geojson into
@@ -39,12 +45,17 @@ interface RegionData {
   validKeys: Set<string>;
   /** region key -> bordering region keys (from public/region-adjacency.json). */
   adjacency: Record<string, string[]>;
+  /** region key -> anchor point (from public/region-centroids.json). */
+  centroids: Record<string, { lat: number; lon: number; spread: number }>;
+  /** region key -> { area (km²), population } (from public/region-geo.json, v0.28 #46). */
+  geo: Record<string, { area: number; population: number }>;
 }
 
 let data: RegionData | null = null;
 
 /**
- * Load (or reload) the region-key manifest, geo, and adjacency. Idempotent.
+ * Load (or reload) the region-key manifest, geo, adjacency, and centroids.
+ * Idempotent.
  * The files are served to the client from `public/` in dev (Vite serves it
  * directly) and from `dist/` in prod (Vite copies `public/*` → `dist/` at build
  * and the Docker image keeps only `dist/`), so probe `public/` then `dist/`
@@ -52,7 +63,10 @@ let data: RegionData | null = null;
  * key manifest + geo. The adjacency manifest is OPTIONAL: when it is missing
  * or broken, `adjacency` stays empty and `neighboursOf`/`hasAdjacency` simply
  * report "no adjacency" (the LLM tool and the frontier prompt field switch
- * off; everything else keeps working). Returns true when the core pair loaded
+ * off; everything else keeps working). The centroid manifest is likewise
+ * OPTIONAL (v0.27, #44): when missing or broken, `centroids` stays empty and
+ * `centroidOf`/`hasCentroids` report "no centroids" (new map markers can't be
+ * placed, but everything else keeps working). Returns true when the core pair loaded
  * cleanly; a missing/broken pair clears the data and returns false so the
  * server still boots and degrades gracefully (expansion becomes a no-op,
  * ownership falls back to the raw input keys).
@@ -61,6 +75,8 @@ export function loadRegions(root: string): boolean {
   const keyFile = 'region-keys.json';
   const geoFile = 'regions.geo.json';
   const adjacencyFile = 'region-adjacency.json';
+  const centroidsFile = 'region-centroids.json';
+  const regionGeoFile = 'region-geo.json';
   const base = [
     path.join(root, 'public'), // dev: Vite serves public/ at /
     path.join(root, 'dist'), // prod: Vite copies public/* -> dist/ (== clientDir)
@@ -74,13 +90,13 @@ export function loadRegions(root: string): boolean {
   const geoPath = path.join(base, geoFile);
   try {
     const idToKey = JSON.parse(readFileSync(keyPath, 'utf8')) as Record<string, string>;
-    const geo = JSON.parse(readFileSync(geoPath, 'utf8')) as {
+    const geoJson = JSON.parse(readFileSync(geoPath, 'utf8')) as {
       features?: Array<{ id?: string | number; properties?: { name?: string; parent?: string } }>;
     };
     const keyToInfo: Record<string, RegionInfo> = {};
     const keysByCountry: Record<string, string[]> = {};
     const validKeys = new Set<string>();
-    for (const f of geo.features ?? []) {
+    for (const f of geoJson.features ?? []) {
       const id = f.id == null ? '' : String(f.id);
       const key = idToKey[id];
       if (!key) continue; // a geo feature with no manifest entry is skipped
@@ -105,7 +121,71 @@ export function loadRegions(root: string): boolean {
       }
     }
 
-    data = { idToKey, keyToInfo, keysByCountry, validKeys, adjacency };
+    // Centroids are optional too (v0.27, #44): a missing/broken file means
+    // "no centroid data" — new markers can't be placed (their adds are
+    // dropped), but everything else keeps working.
+    let centroids: Record<string, { lat: number; lon: number; spread: number }> = {};
+    const centroidsPath = path.join(base, centroidsFile);
+    if (existsSync(centroidsPath)) {
+      try {
+        const raw = JSON.parse(readFileSync(centroidsPath, 'utf8')) as Record<
+          string,
+          { lat?: unknown; lon?: unknown; spread?: unknown }
+        >;
+        // Keep only well-formed entries; a corrupt file degrades to "none".
+        for (const [k, v] of Object.entries(raw)) {
+          if (
+            v &&
+            typeof v.lat === 'number' &&
+            typeof v.lon === 'number' &&
+            typeof v.spread === 'number' &&
+            Number.isFinite(v.lat) &&
+            Number.isFinite(v.lon) &&
+            Number.isFinite(v.spread)
+          ) {
+            centroids[k] = { lat: v.lat, lon: v.lon, spread: v.spread };
+          }
+        }
+      } catch (err) {
+        console.error('[regions] failed to load region-centroids.json, continuing without it', err);
+        centroids = {};
+      }
+    }
+
+    // The region-geo manifest (v0.28, #46): area (km²) + population per region
+    // key — the weighting source for the per-region stats model. OPTIONAL like
+    // the others: a missing/broken file means "no geo data", and weighting
+    // degrades to uniform (every region weight 1) while everything else keeps
+    // working.
+    let geo: Record<string, { area: number; population: number }> = {};
+    const geoDataPath = path.join(base, regionGeoFile);
+    if (existsSync(geoDataPath)) {
+      try {
+        const raw = JSON.parse(readFileSync(geoDataPath, 'utf8')) as Record<
+          string,
+          { area?: unknown; population?: unknown }
+        >;
+        // Keep only well-formed entries; a corrupt file degrades to "none".
+        for (const [k, v] of Object.entries(raw)) {
+          if (
+            v &&
+            typeof v.area === 'number' &&
+            Number.isFinite(v.area) &&
+            v.area >= 0 &&
+            typeof v.population === 'number' &&
+            Number.isFinite(v.population) &&
+            v.population >= 0
+          ) {
+            geo[k] = { area: v.area, population: v.population };
+          }
+        }
+      } catch (err) {
+        console.error('[regions] failed to load region-geo.json, continuing without it', err);
+        geo = {};
+      }
+    }
+
+    data = { idToKey, keyToInfo, keysByCountry, validKeys, adjacency, centroids, geo };
     return validKeys.size > 0;
   } catch (err) {
     console.error('[regions] failed to load region data', err);
@@ -189,6 +269,47 @@ export function hasAdjacency(): boolean {
   return data !== null && Object.keys(data.adjacency).length > 0;
 }
 
+/**
+ * True when the region-centroid manifest loaded with at least one entry
+ * (v0.27, #44). The server's jump route uses this to decide whether to hand
+ * the engine a centroid resolver (which lets a turn place new map markers)
+ * or skip marker placement (existing markers are still maintained).
+ */
+export function hasCentroids(): boolean {
+  return data !== null && Object.keys(data.centroids).length > 0;
+}
+
+/**
+ * True when the region-geo manifest loaded with at least one entry (v0.28,
+ * #46). The server's jump route uses this to decide whether to hand the
+ * engine a geo resolver (which weights the per-region stats derivation by
+ * area×population) or fall back to a uniform (unweighted) median.
+ */
+export function hasGeo(): boolean {
+  return data !== null && Object.keys(data.geo).length > 0;
+}
+
+/**
+ * The precomputed anchor point for a region key: the centroid of its
+ * largest-area part, plus a `spread` (≈ 0.1 × that part's smallest bbox
+ * dimension, in degrees) the engine scatters markers within
+ * ±(spread/2) of the centroid. `undefined` for an unknown key or when no
+ * centroid data is loaded (v0.27, #44).
+ */
+export function centroidOf(key: string): { lat: number; lon: number; spread: number } | undefined {
+  return data?.centroids[key];
+}
+
+/**
+ * The precomputed area (km²) + population for a region key (v0.28, #46) — the
+ * weighting source for the per-region stats model. `undefined` for an unknown
+ * key or when no geo data is loaded (the derivation then falls back to a
+ * uniform weight of 1 for that region).
+ */
+export function geoOf(key: string): { area: number; population: number } | undefined {
+  return data?.geo[key];
+}
+
 /**
  * The union of the region keys that share a land border with any of the given
  * keys — deduplicated, the queried keys themselves excluded, and sorted for

server/stub.ts

@@ -31,6 +31,13 @@ export interface StubPayload {
    * is covered by unit tests against applyTurnResult, not by the stub.
    */
   unowned?: string[];
+  /**
+   * (v0.27, #44) Current map markers (`{ id, type, name, regionKey, owner }`),
+   * emitted by the engine's user prompt. The stub ignores this field — it
+   * never places or removes a marker (see deterministicTurn), so the marker
+   * path is covered by unit tests against applyTurnResult, not by the stub.
+   */
+  markers?: Array<{ id: string; type: string; name: string; regionKey: string; owner: string | null }>;
 }
 
 function truncate(s: string, n: number): string {
@@ -61,6 +68,10 @@ function truncate(s: string, n: number): string {
  * (v0.23, #16 P4a) The stub likewise NEVER proposes nation-management ops (it
  * always returns `nationOps: []`) — the propose→confirm/reject flow is
  * covered by unit tests only, keeping the e2e assertions untouched.
+ *
+ * (v0.27, #44) The stub likewise NEVER places or removes a map marker (it
+ * always returns `markers: { add: [], remove: [] }`) — the marker path is
+ * covered by unit tests only, keeping the e2e assertions untouched.
  */
 export function deterministicTurn(p: StubPayload): TurnResult {
   const state = p.state;
@@ -126,6 +137,7 @@ export function deterministicTurn(p: StubPayload): TurnResult {
     territoryChanges,
     unowned: [], // the stub never creates no man's land (see doc comment)
     nationOps: [], // the stub never proposes nation ops (see doc comment)
+    markers: { add: [], remove: [] }, // the stub never touches markers (see doc comment)
   };
 }
 

shared/protocol.ts

@@ -6,10 +6,14 @@ import type {
   EventOutcome,
   EventType,
   GameState,
+  MarkerType,
   Nation,
+  NationStats,
   RelationStatus,
+  RegionStats,
   StatKey,
 } from './types';
+import { MARKER_TYPES, STAT_KEYS } from './types';
 
 /** A numeric change to one of a nation's 0–100 stats. */
 export type StateChange =
@@ -30,15 +34,14 @@ export interface TerritoryChange {
   lose: string[];
 }
 
-// --- Nation-management ops (v0.23, #16 P4a: the hybrid "LLM proposes, player
-// confirms" model) -----------------------------------------------------------
+// --- Nation-management ops (v0.23 P4a / v0.24 P4b, #16: the hybrid "LLM
+// proposes, player confirms" model) ------------------------------------------
 //
 // Unlike stat / relation / territory deltas, a NationOp proposed in a turn is
 // NOT applied by that turn. It is stored as a *pending proposal* in
 // `GameState.pendingNationOps` and only takes effect when the player confirms
-// it (optionally editing it) or is dropped when the player rejects it. Rename
-// is implemented in v0.23 (P4a); split and merge are declared here so the union
-// is stable for P4b, and are defensively accepted-but-not-applied until then.
+// it (optionally editing it) or is dropped when the player rejects it. All
+// three kinds are implemented: rename (v0.23 P4a), split and merge (v0.24 P4b).
 
 /**
  * The identity reference a nation is addressed by inside a {@link NationOp}.
@@ -63,9 +66,13 @@ export interface RenameOp {
 }
 
 /**
- * A **split** proposal (declared for #16 P4b; **not** applied by the engine yet
- * — it is accepted into the pending list, but confirming it is a no-op until
- * P4b lands). Describes the new nations a source nation is divided into.
+ * A **split** proposal (v0.24, #16 P4b). Describes the new nations a source
+ * nation is divided into. On confirm the source is dissolved: each part gets a
+ * fresh id, the region keys it was given (restricted to keys the source
+ * actually owns — first claim wins), fresh baseline stats, and a copy of the
+ * source's relations; any of the source's unclaimed keys go to `parts[0]`.
+ * When the source is the player's own nation the player chooses which part
+ * they lead (the confirm request's `edits.playerPart`, default `parts[0]`).
  */
 export interface SplitOp {
   kind: 'split';
@@ -76,9 +83,13 @@ export interface SplitOp {
 }
 
 /**
- * A **merge** proposal (declared for #16 P4b; **not** applied by the engine yet
- * — accepted into the pending list, no-op on confirm until P4b). Folds several
- * nations into a single surviving nation.
+ * A **merge** proposal (v0.24, #16 P4b). Folds several nations into a single
+ * surviving nation. On confirm the survivor keeps its id (renamed to `into`,
+ * or to the confirm request's `edits.name`), its territory becomes the union
+ * of all inputs' territories, it keeps its own stats, and it inherits the
+ * union of all inputs' relations (its own winning per third party, else the
+ * first input's); every non-survivor input is removed. If the player's nation
+ * was a non-survivor input the player pointer is re-pointed to the survivor.
  */
 export interface MergeOp {
   kind: 'merge';
@@ -93,8 +104,8 @@ export interface MergeOp {
 /**
  * A structural operation on the set of nations that the LLM may propose in a
  * turn (`TurnResult.nationOps`). See the section comment above for the hybrid
- * propose→confirm semantics. Rename is implemented (P4a); split/merge are
- * declared for P4b and are a safe no-op until then.
+ * propose→confirm semantics. All three kinds are implemented: rename (P4a),
+ * and split / merge (P4b, v0.24).
  */
 export type NationOp = RenameOp | SplitOp | MergeOp;
 
@@ -107,6 +118,100 @@ export interface TurnEventSpec {
   outcome: EventOutcome;
 }
 
+// --- Map markers (v0.27, #44) -------------------------------------------------
+//
+// The LLM places named point markers (cities, factories, armies, ports,
+// capitals, fleets, rocket launch sites, gatherings) anchored to a region
+// key. It never sees or sets coordinates: the engine derives the position
+// from the region's precomputed centroid (public/region-centroids.json) plus a
+// small deterministic offset, and it recomputes each marker's owner from the
+// region's current owner on every turn (a released region → null).
+//
+// The marker id is a STABLE, deterministic 4-letter code (FNV-1a 32-bit →
+// base 26, the same scheme as the region keys' 4-char suffix) derived from
+// (type, name, regionKey) — so re-adding an identical marker is idempotent
+// (same id, skipped) and removing by id is unambiguous.
+
+/** The spec the LLM emits to place a marker: type, name and the region it sits in. */
+export interface MarkerSpec {
+  type: MarkerType;
+  name: string;
+  regionKey: string;
+}
+
+/**
+ * One existing marker as the user prompt presents it to the model (v0.27,
+ * #44): its stable `id` (the model may echo it in `TurnResult.markers.remove`),
+ * type, name, region key, and the id of the nation currently owning its
+ * region (`null` when the region is unowned / no man's land).
+ */
+export interface MarkerInfo {
+  id: string;
+  type: MarkerType;
+  name: string;
+  regionKey: string;
+  owner: string | null;
+}
+
+/**
+ * The per-type presentation of a marker: its display label (tooltip /
+ * dossier), its color, and its glyph character (a symbol-layer text label —
+ * a small, font-safe character in front of the name). Pure + shared so the
+ * client's marker layer and any server-side consumers agree on the look.
+ */
+export const MARKER_TYPE_INFO: Record<MarkerType, { label: string; color: string; glyph: string }> = {
+  city: { label: 'City', color: '#cbd5e1', glyph: '●' },
+  factory: { label: 'Factory', color: '#fb923c', glyph: '■' },
+  army: { label: 'Army', color: '#ef4444', glyph: '▲' },
+  port: { label: 'Port', color: '#38bdf8', glyph: '◆' },
+  capital: { label: 'Capital', color: '#fbbf24', glyph: '★' },
+  fleet: { label: 'Fleet', color: '#22d3ee', glyph: '◗' },
+  rocket: { label: 'Rocket site', color: '#a78bfa', glyph: '↥' },
+  gathering: { label: 'Gathering', color: '#4ade80', glyph: '◉' },
+};
+
+/** Hard cap on a game's total markers (new adds beyond the cap are dropped, v0.27 #44). */
+export const MAX_MARKERS = 400;
+
+/**
+ * FNV-1a 32-bit — the same tiny, stable, pure string hash the region keys use
+ * (see scripts/build-region-keys.mjs). Exported so the engine can derive
+ * deterministic per-axis jitter fractions from it (marker placement, v0.27 #44).
+ */
+export function fnv1a32(str: string): number {
+  let h = 0x811c9dc5;
+  for (let i = 0; i < str.length; i++) {
+    h ^= str.charCodeAt(i);
+    h = Math.imul(h, 0x01000193) >>> 0;
+  }
+  return h >>> 0;
+}
+
+/** Spread a 32-bit hash across four lowercase letters (base 26 per byte). */
+function code4(h: number): string {
+  let out = '';
+  for (let i = 0; i < 4; i++) {
+    out += String.fromCharCode(97 + (((h >>> (i * 8)) & 0xff) % 26));
+  }
+  return out;
+}
+
+/**
+ * The stable id for a marker: 4 base-26 lowercase chars from the FNV-1a hash
+ * of `(type, name, regionKey)` (NUL-separated so no field boundary is
+ * ambiguous). Deterministic across runs and platforms (pure string math), so
+ * the same (type, name, regionKey) always maps to the same id — re-adding is
+ * idempotent, removing by id is unambiguous.
+ */
+export function markerId(type: MarkerType, name: string, regionKey: string): string {
+  return code4(fnv1a32(`${type}\u0000${name}\u0000${regionKey}`));
+}
+
+/** True when `t` is one of the eight known marker types (v0.27, #44). */
+export function isMarkerType(t: unknown): t is MarkerType {
+  return typeof t === 'string' && (MARKER_TYPES as string[]).includes(t);
+}
+
 /** The exact JSON object the world-simulator LLM must return for a turn. */
 export interface TurnResult {
   date: string;
@@ -125,14 +230,25 @@ export interface TurnResult {
    */
   unowned: string[];
   /**
-   * (v0.23, #16 P4a) Nation-management ops the LLM proposes this turn. These
-   * are NOT applied by the turn: each is appended to
+   * (v0.23 P4a / v0.24 P4b, #16) Nation-management ops the LLM proposes this
+   * turn. These are NOT applied by the turn: each is appended to
    * `GameState.pendingNationOps` as a proposal awaiting the player's
-   * confirm/reject. Rename is the only kind the engine currently applies;
-   * split/merge are declared for P4b and are accepted-but-dropped. Empty on
-   * turns where the model proposes none.
+   * confirm/reject. All three kinds (rename, split, merge) are implemented —
+   * a confirmed rename changes `Nation.name`; a confirmed split dissolves the
+   * source into its parts; a confirmed merge folds its inputs into the
+   * survivor. Empty on turns where the model proposes none.
    */
   nationOps: NationOp[];
+  /**
+   * (v0.27, #44) Map-marker ops this turn. `add` places new named markers
+   * (the engine positions each at its region's centroid + a small
+   * deterministic offset, sets the owner to the region's post-turn owner,
+   * derives the stable id, and drops unknown types/region keys, duplicates,
+   * and adds beyond MAX_MARKERS); `remove` drops markers by their stable id
+   * (a no-op for an id that is not present). Both required, `[]` on turns
+   * with no marker activity.
+   */
+  markers: { add: MarkerSpec[]; remove: string[] };
 }
 
 /** Per-region map payload: region key -> owning nation + its stable color. */
@@ -240,15 +356,22 @@ export interface RemoveQueueItemResponse {
 }
 
 /**
- * (v0.23, #16 P4a) Confirm a pending nation-op proposal by its index in
- * `game.pendingNationOps`. A rename takes effect (the player may override the
- * proposed name via `edits.name`); split/merge proposals are a no-op on
- * confirm until P4b. No LLM call, no turn advance.
+ * (v0.23 P4a / v0.24 P4b, #16) Confirm a pending nation-op proposal by its
+ * index in `game.pendingNationOps`. A rename takes effect (the player may
+ * override the proposed name via `edits.name`); a split and a merge are fully
+ * applied (v0.24 P4b). No LLM call, no turn advance.
  */
 export interface ConfirmNationOpRequest {
   index: number;
-  /** Optional player edits applied on confirm (rename: the final display name). */
-  edits?: { name?: string };
+  /**
+   * Optional player edits applied on confirm.
+   * - `name`: the final display name — overrides a rename's `to`, a merge's
+   *   `into`, or (for a split) the name of the part the player leads.
+   * - `playerPart`: for a split of the player's own nation, which part (index
+   *   into the op's `parts`) the player will lead (default `0` when missing or
+   *   out of range, so the player is never orphaned).
+   */
+  edits?: { name?: string; playerPart?: number };
 }
 export interface ConfirmNationOpResponse {
   game: GameState;
@@ -394,3 +517,137 @@ export function nationForPrompt(n: Nation) {
     relations: n.relations,
   };
 }
+
+// --- Per-region stats (v0.28, #46) ------------------------------------------
+//
+// A nation's 0–100 `NationStats` are no longer stored as independent per-nation
+// values: they are DERIVED as the area×population-weighted median of the stats
+// of the regions the nation owns (`GameState.regionStats`, keyed by region key).
+// These pure helpers implement that derivation, the fresh-game / legacy seeding,
+// and the one-time migration of a pre-v0.28 row. They have no runtime deps.
+
+/**
+ * The weighted median of `values` with per-value `weights` (paired by index).
+ * The pairs are sorted by value ascending and the result is the value at the
+ * first point where the cumulative weight reaches at least half the total
+ * weight. An empty input, or a total weight of zero, yields 0. Non-finite or
+ * non-positive weights are treated as 0 (excluded from the median).
+ * Translation-invariant: adding a constant to every value shifts the result by
+ * that constant — so the median of a set of **identical** values is that value
+ * (the invariant the equal-value seeding and legacy migration rely on).
+ * Pure + shared.
+ */
+export function weightedMedian(values: number[], weights: number[]): number {
+  if (values.length === 0) return 0;
+  const pairs = values
+    .map((v, i) => {
+      const w =
+        typeof weights[i] === 'number' && Number.isFinite(weights[i]) && weights[i] > 0
+          ? weights[i]
+          : 0;
+      return { v: Number.isFinite(v) ? v : 0, w };
+    })
+    .filter((p) => p.w > 0);
+  if (pairs.length === 0) return 0;
+  const total = pairs.reduce((s, p) => s + p.w, 0);
+  if (total <= 0) return 0;
+  pairs.sort((a, b) => a.v - b.v);
+  let cum = 0;
+  for (const p of pairs) {
+    cum += p.w;
+    if (cum >= total / 2) return p.v;
+  }
+  return pairs[pairs.length - 1]!.v;
+}
+
+/**
+ * Derive a nation's aggregate {@link NationStats} from the stats of the regions
+ * it owns: each of the four stats is the **area×population-weighted median**
+ * (see {@link weightedMedian}) over the nation's owned region keys. A region's
+ * weight is `(area > 0 ? area : 1) × (population > 0 ? population : 1)` — both
+ * factors fall back to 1 when the region has no geo entry (`geoOf` returns
+ * `undefined` for it), so every region carries weight ≥ 1 and a missing geo
+ * degrades gracefully to a uniform (unweighted) median. A region key with no
+ * `regionStats` entry is skipped. Returns the zero stats when the nation owns
+ * no region with a stats entry (the caller's 0-region guard keeps the nation's
+ * directly-maintained `n.stats` in that case). Pure + shared.
+ */
+export function deriveNationStats(
+  regionKeys: string[],
+  regionStats: Record<string, RegionStats>,
+  geoOf?: (key: string) => { area: number; population: number } | undefined,
+): NationStats {
+  const zero: NationStats = { military: 0, economy: 0, stability: 0, population: 0 };
+  const byStat: Record<StatKey, number[]> = {
+    military: [],
+    economy: [],
+    stability: [],
+    population: [],
+  };
+  const weights: number[] = [];
+  for (const key of regionKeys) {
+    const rs = regionStats[key];
+    if (!rs) continue; // a key with no per-region stats is skipped
+    const g = geoOf?.(key);
+    const a = g && g.area > 0 ? g.area : 1;
+    const p = g && g.population > 0 ? g.population : 1;
+    weights.push(a * p);
+    for (const k of STAT_KEYS) byStat[k].push(rs[k]);
+  }
+  if (weights.length === 0) return zero;
+  const out: NationStats = { military: 0, economy: 0, stability: 0, population: 0 };
+  for (const k of STAT_KEYS) out[k] = clampStat(weightedMedian(byStat[k], weights));
+  return out;
+}
+
+/**
+ * Seed a per-region stats table from a set of nations (used both at game
+ * creation and by the legacy migration): every owned region key gets a **copy**
+ * of its owner's current `NationStats`, so a fresh nation's regions all start
+ * identical (the weighted median of identical values is that value, so the
+ * derived `n.stats` equals the seeded one). A region with two or more owners
+ * (corrupt) is seeded by the first owner encountered; a key owned by nobody gets
+ * no entry. Pure + shared.
+ */
+export function seedRegionStats(nations: Record<string, Nation>): Record<string, RegionStats> {
+  const out: Record<string, RegionStats> = {};
+  for (const n of Object.values(nations)) {
+    for (const key of n.territory) {
+      if (!(key in out)) out[key] = { ...n.stats }; // first owner wins (sole ownership holds normally)
+    }
+  }
+  return out;
+}
+
+/**
+ * (v0.28, #46) One-time migration of a **legacy** (pre-v0.28) `GameState` row
+ * into the per-region-stats model, returning a new state (the input is never
+ * mutated):
+ *  - a row that already has `regionStats` (a v0.28+ save) is returned
+ *    **UNCHANGED** — its `Nation.stats` are already the correct derived medians
+ *    and must not be recomputed on load (that would drift them);
+ *  - a legacy row (`regionStats` absent at runtime) seeds every owned region key
+ *    with a copy of its owner's current stats (so each nation's regions start
+ *    identical), then recomputes each nation's stats as the weighted median of
+ *    its regions (a 0-region nation keeps its stats). Without `geoOf` the
+ *    weighting is uniform, which is weight-invariant for the identical-value
+ *    case, so the recomputed stats equal the originals — the migration is a
+ *    no-op on the visible numbers and only materializes the (previously
+ *    implicit) per-region values. Never throws.
+ */
+export function migrateRegionStats(
+  state: GameState,
+  geoOf?: (key: string) => { area: number; population: number } | undefined,
+): GameState {
+  // A v0.28+ row already carries per-region stats: leave it exactly as saved.
+  if (state.regionStats !== undefined) return state;
+  // Legacy row: materialize per-region stats from each nation's (uniform) stats.
+  const next: GameState = { ...state, regionStats: seedRegionStats(state.nations) };
+  for (const n of Object.values(next.nations)) {
+    if (n.territory.length === 0) continue; // 0-region guard: keep its stats
+    if (n.territory.some((k) => next.regionStats[k])) {
+      n.stats = deriveNationStats(n.territory, next.regionStats, geoOf);
+    }
+  }
+  return next;
+}

shared/types.ts

@@ -13,6 +13,19 @@ export interface NationStats {
   population: number;
 }
 
+/**
+ * (v0.28, #46) The 0–100 status indices of a **single region**. Per-region stats
+ * are the unit of record: a nation's aggregate {@link NationStats} is derived as
+ * the area×population-weighted median of the stats of the regions it owns (see
+ * `protocol.deriveNationStats`). Every value is clamped to 0–100 by the engine.
+ */
+export interface RegionStats {
+  military: number;
+  economy: number;
+  stability: number;
+  population: number;
+}
+
 export const STAT_KEYS = ['military', 'economy', 'stability', 'population'] as const;
 export type StatKey = (typeof STAT_KEYS)[number];
 
@@ -68,6 +81,60 @@ export const EVENT_TYPES: EventType[] = [
 
 export type EventOutcome = 'success' | 'failure' | 'partial' | 'neutral';
 
+// --- Map markers (v0.27, #44) -------------------------------------------------
+//
+// Named point markers the LLM can place on the map (cities, factories, armies,
+// ports, capitals, fleets, rocket launch sites, political/social gatherings).
+// A marker is anchored to a **region key** (see `public/region-keys.json`): the
+// engine positions it at that region's precomputed centroid (with a small
+// deterministic offset) and its `ownerNationId` follows the region's current
+// owner (recomputed on every turn; `null` when the region is unowned / no
+// man's land). See protocol.ts for the LLM-facing `TurnResult.markers`
+// contract and the `markerId` derivation.
+
+/** The eight marker categories the model may place (v0.27, #44). */
+export type MarkerType =
+  | 'city'
+  | 'factory'
+  | 'army'
+  | 'port'
+  | 'capital'
+  | 'fleet'
+  | 'rocket'
+  | 'gathering';
+
+/** All marker types, in canonical order (used by the LLM contract + map layer). */
+export const MARKER_TYPES: MarkerType[] = [
+  'city',
+  'factory',
+  'army',
+  'port',
+  'capital',
+  'fleet',
+  'rocket',
+  'gathering',
+];
+
+/**
+ * A named point marker on the map (v0.27, #44). `id` is a stable,
+ * deterministic 4-character code derived from `type + name + regionKey`
+ * (see protocol.markerId) — re-adding the same marker is idempotent and
+ * removing by id is unambiguous. `lat`/`lon` are filled in by the engine from
+ * the region's centroid manifest (never by the model); `ownerNationId` is the
+ * marker's region's current owner (`null` when unowned) and is recomputed by
+ * the engine on every committed turn, so a marker always follows its region.
+ */
+export interface MapMarker {
+  id: string;
+  type: MarkerType;
+  name: string;
+  regionKey: string;
+  lat: number;
+  lon: number;
+  ownerNationId: string | null;
+  placedTurn: number;
+}
+
 /** A narrative event the simulation emitted on some turn. */
 export interface EventEntry {
   id: string;
@@ -138,20 +205,44 @@ export interface GameState {
    */
   unowned: string[];
   /**
-   * (v0.23, #16 P4a) Nation-management ops the LLM has proposed but the player
-   * has not yet resolved: a *pending proposal* list, as opposed to `pending`
-   * (the current round's queued player actions). A turn NEVER applies one —
-   * `applyTurnResult` appends the turn's `nationOps` to this list, and each
-   * proposal survives across turns until the player resolves it: confirming
-   * applies it (a rename changes `Nation.name` only — the id, its territory,
-   * its relations, and the player pointer all stay valid) and removes it;
-   * rejecting removes it without applying. Split/merge are declared for P4b
-   * and are a safe no-op on confirm until then. Always `[]` on a fresh game;
-   * rows saved before v0.23 load with this defaulted to `[]` (see server/db.ts).
-   * (The `NationOp` type lives in protocol.ts; the import there is type-only,
-   * so this file still has no runtime dependencies.)
+   * (v0.23, #16 P4a; v0.24, #16 P4b) Nation-management ops the LLM has
+   * proposed but the player has not yet resolved: a *pending proposal* list,
+   * as opposed to `pending` (the current round's queued player actions). A
+   * turn NEVER applies one — `applyTurnResult` appends the turn's
+   * `nationOps` to this list, and each proposal survives across turns until
+   * the player resolves it: confirming applies it (a rename changes
+   * `Nation.name` only; a split partitions the nation's region-key territory
+   * into the new nations' territories; a merge folds the inputs' territory
+   * into the survivor) and removes it; rejecting removes it without
+   * applying. Always `[]` on a fresh game; rows saved before v0.23 load with
+   * this defaulted to `[]` (see server/db.ts). (The `NationOp` type lives in
+   * protocol.ts; the import there is type-only, so this file still has no
+   * runtime dependencies.)
    */
   pendingNationOps: NationOp[];
+  /**
+   * (v0.27, #44) Named point markers on the map: the LLM places them (via a
+   * turn's `markers.add`) and removes them (`markers.remove`, by id). The
+   * engine positions each at its region's centroid (deterministic small
+   * offset) and recomputes `ownerNationId` from the region's current owner on
+   * EVERY committed turn (a released region → `null`). Always `[]` on a fresh
+   * game; rows saved before v0.27 load with this defaulted to `[]` (see
+   * server/db.ts) — additive, no data wipe. Capped at protocol.MAX_MARKERS.
+   */
+  markers: MapMarker[];
+  /**
+   * (v0.28, #46) Per-region stats, keyed by **region key** (see
+   * `public/region-keys.json`): each owned region carries its own four 0–100
+   * stats, and a nation's aggregate `Nation.stats` is the area×population-
+   * weighted median of the regions it owns (see `protocol.deriveNationStats`).
+   * A region that ends a turn **unowned** (released to no man's land) has NO
+   * entry, and a preset-unassigned region (never owned) has none until first
+   * claimed (re-claiming re-inits it to the gainer's stats). Always present on a
+   * fresh game (every owned region seeded with its owner's initial stats); a
+   * legacy SQLite row without the field is migrated at load (see server/db.ts)
+   * — additive, no data wipe.
+   */
+  regionStats: Record<string, RegionStats>;
 }
 
 /**

src/App.tsx

@@ -405,11 +405,12 @@ export default function App() {
     [game, applyState],
   );
 
-  // Apply a pending nation op the model proposed (confirm, with an optional
-  // rename-name edit). Fast, non-LLM — gated by `opBusy`, not `busy`. The
-  // version-bumped state comes back in the response and the SSE `state` event.
+  // Apply a pending nation op the model proposed (confirm; `edits.name`
+  // overrides a rename/merge name, `edits.playerPart` picks the player's
+  // successor part in a split). Fast, non-LLM — gated by `opBusy`, not `busy`.
+  // The version-bumped state comes back in the response and the SSE `state` event.
   const runConfirmNationOp = useCallback(
-    async (index: number, edits?: { name?: string }) => {
+    async (index: number, edits?: { name?: string; playerPart?: number }) => {
       if (!game) return;
       setOpBusy(true);
       try {
@@ -603,7 +604,7 @@ interface GameScreenProps {
   onRemoveQueueItem: (index: number) => void;
   onAdvisor: (p?: string) => void;
   onJump: () => void;
-  onConfirmNationOp: (index: number, edits?: { name?: string }) => void;
+  onConfirmNationOp: (index: number, edits?: { name?: string; playerPart?: number }) => void;
   onRejectNationOp: (index: number) => void;
   onHome: () => void;
 }
@@ -705,6 +706,7 @@ function GameScreen({
         nations={game.nations}
         presetId={game.presetId}
         unowned={game.unowned ?? []}
+        markers={game.markers ?? []}
         onFocusNation={focusNation}
       />
 

src/components/ActionPanel.tsx

@@ -44,8 +44,12 @@ interface Props {
   onAdvisor: (prompt?: string) => void;
   /** Commit the whole pending round in a single LLM turn. */
   onJump: () => void;
-  /** Apply a pending nation op; `edits.name` optionally overrides a rename. */
-  onConfirmNationOp: (index: number, edits?: { name?: string }) => void;
+  /**
+   * Apply a pending nation op: `edits.name` overrides a rename's target name
+   * (or a merge's name); `edits.playerPart` picks the player's successor part
+   * in a split (default 0).
+   */
+  onConfirmNationOp: (index: number, edits?: { name?: string; playerPart?: number }) => void;
   /** Drop (reject) a pending nation op by its index. */
   onRejectNationOp: (index: number) => void;
   /**

src/components/NationOpDialog.tsx

@@ -19,8 +19,12 @@ interface Props {
   onOpenChange: (open: boolean) => void;
   /** A confirm/reject request is in flight — disable the per-op controls. */
   opBusy: boolean;
-  /** Apply a pending op; `edits.name` optionally overrides a rename's target name. */
-  onConfirm: (index: number, edits?: { name?: string }) => void;
+  /**
+   * Apply a pending op: `edits.name` overrides a rename's target name (or the
+   * merged name for a merge); `edits.playerPart` picks which new part the
+   * player's nation becomes in a split (default 0).
+   */
+  onConfirm: (index: number, edits?: { name?: string; playerPart?: number }) => void;
   /** Drop a pending op (reject / dismiss). */
   onReject: (index: number) => void;
 }
@@ -37,10 +41,12 @@ function describeOp(op: NationOp, name: (ref: string) => string): string {
 
 /**
  * Reviews the nation ops the LLM has proposed (stored in `pendingNationOps`)
- * and lets the player apply ("LLM proposes, player confirms") or drop each one.
- * A rename shows the model's proposed name in an editable field (so the player
- * can tweak it before confirming); split and merge are declared but not yet
- * applied (P4b) — they can be dismissed but not confirmed.
+ * and lets the player apply ("LLM proposes, player confirms") or drop each one:
+ * a rename shows the proposed name in an editable field; a split lists the
+ * proposed parts (with the number of regions each is assigned) and, when the
+ * split parent is the player's own nation, radio buttons to pick which new
+ * part the player leads; a merge shows the input nations (the survivor
+ * highlighted) and an editable name for the merged state (default `into`).
  */
 export default function NationOpDialog({
   game,
@@ -52,9 +58,24 @@ export default function NationOpDialog({
 }: Props) {
   const ops = game.pendingNationOps;
   const name = (ref: string) => game.nations[ref]?.name ?? ref;
-  // The player's edit to a rename's target name, keyed by pending-op index.
-  // An unset entry means "use the model's proposed name" (`op.to`).
+  // Resolve a nation ref the way the server does (id first, then a unique
+  // case-insensitive name; null when unknown/ambiguous) — UI hints only, the
+  // server stays authoritative.
+  const resolveRef = (ref: string): string | null => {
+    const r = (ref ?? '').trim();
+    if (!r) return null;
+    if (game.nations[r]) return r;
+    const matches = Object.values(game.nations).filter(
+      (n) => n.name.trim().toLowerCase() === r.toLowerCase(),
+    );
+    return matches.length === 1 ? matches[0].id : null;
+  };
+  // The player's edits, keyed by pending-op index: the rename/merge target
+  // name (an unset entry means "use the model's proposed name"), and which
+  // split part the player succeeds to (preselected 0 — the radio is
+  // "required" and always has a valid answer).
   const [edits, setEdits] = useState<Record<number, string>>({});
+  const [playerParts, setPlayerParts] = useState<Record<number, number>>({});
 
   return (
     <Dialog open={open} onOpenChange={onOpenChange}>
@@ -68,7 +89,8 @@ export default function NationOpDialog({
           </DialogTitle>
           <DialogDescription>
             The model proposed changes to nations. Confirm to apply them (you can edit a
-            rename) or reject to leave the world as it is.
+            name and choose your successor state in a split) or reject to leave the world
+            as it is.
           </DialogDescription>
         </DialogHeader>
 
@@ -80,7 +102,34 @@ export default function NationOpDialog({
           <ul className="max-h-[50vh] space-y-2.5 overflow-y-auto pr-1" data-testid="nation-op-list">
             {ops.map((op, i) => {
               const isRename = op.kind === 'rename';
+              const isSplit = op.kind === 'split';
+              const isMerge = op.kind === 'merge';
               const finalName = isRename ? (edits[i] ?? (op as RenameOp).to).trim() : '';
+              // Split: is the parent the player's own nation? (the successor radio
+              // is offered only in that case — the engine ignores playerPart otherwise)
+              const splitParentIsPlayer =
+                isSplit && resolveRef((op as { nationRef: string }).nationRef) === game.playerNationId;
+              const playerPart = playerParts[i] ?? 0;
+              // Merge: the survivor (highlighted) and whether the proposal is
+              // even valid (2+ distinct inputs; the survivor among them).
+              const survivorId = isMerge ? resolveRef((op as { survivingRef: string }).survivingRef) : null;
+              const inputIds = isMerge
+                ? new Set(
+                    (op as { nationRefs: string[] }).nationRefs
+                      .map(resolveRef)
+                      .filter((x): x is string => x !== null),
+                  )
+                : new Set<string>();
+              const mergeValid =
+                !isMerge || (inputIds.size >= 2 && (survivorId !== null && inputIds.has(survivorId)));
+              const mergeName = isMerge ? (edits[i] ?? (op as { into: string }).into).trim() : '';
+
+              const confirm = () => {
+                if (isRename) onConfirm(i, finalName ? { name: finalName } : undefined);
+                else if (isMerge) onConfirm(i, mergeName ? { name: mergeName } : undefined);
+                else onConfirm(i, splitParentIsPlayer ? { playerPart } : undefined);
+              };
+
               return (
                 <li
                   key={`${i}-${op.kind}`}
@@ -96,6 +145,7 @@ export default function NationOpDialog({
                       {describeOp(op, name)}
                     </span>
                   </div>
+
                   {isRename ? (
                     <div className="space-y-2.5">
                       <Input
@@ -118,7 +168,72 @@ export default function NationOpDialog({
                         </Button>
                         <Button
                           size="sm"
-                          onClick={() => onConfirm(i, finalName ? { name: finalName } : undefined)}
+                          onClick={confirm}
+                          disabled={opBusy}
+                          data-testid="nation-op-confirm"
+                        >
+                          {opBusy ? <Loader2 className="size-3.5 animate-spin" /> : <Check className="size-3.5" />}
+                          Confirm
+                        </Button>
+                      </div>
+                    </div>
+                  ) : isSplit ? (
+                    <div className="space-y-2.5">
+                      <div className="space-y-1">
+                        {(op as { parts: { name: string; territory?: string[] }[] }).parts.map((p, pi) => (
+                          <div
+                            key={pi}
+                            className="flex items-center gap-2 text-sm"
+                            data-testid="nation-op-part"
+                            data-part={pi}
+                          >
+                            {splitParentIsPlayer ? (
+                              <input
+                                type="radio"
+                                name={`player-part-${i}`}
+                                checked={playerPart === pi}
+                                onChange={() => setPlayerParts((prev) => ({ ...prev, [i]: pi }))}
+                                disabled={opBusy}
+                                className="size-3.5 shrink-0 accent-amber-400"
+                                aria-label={`Make ${p.name} the player's successor state`}
+                                data-testid="nation-op-player-part"
+                              />
+                            ) : (
+                              <span className="size-3.5 shrink-0" aria-hidden />
+                            )}
+                            <span className="min-w-0 flex-1 truncate">{p.name}</span>
+                            <span className="shrink-0 text-[11px] tabular-nums text-muted-foreground">
+                              {p.territory?.length ?? 0} region{(p.territory?.length ?? 0) === 1 ? '' : 's'}
+                            </span>
+                          </div>
+                        ))}
+                      </div>
+                      {splitParentIsPlayer && (
+                        <p className="text-[11px] text-muted-foreground" data-testid="nation-op-split-hint">
+                          Choose which new state you will lead after the split.
+                        </p>
+                      )}
+                      {(op as { parts: unknown[] }).parts.length < 2 && (
+                        <p className="text-[11px] text-muted-foreground">
+                          This split names fewer than two parts — confirming will dismiss it
+                          without changing the world.
+                        </p>
+                      )}
+                      <div className="flex justify-end gap-2">
+                        <Button
+                          variant="ghost"
+                          size="sm"
+                          onClick={() => onReject(i)}
+                          disabled={opBusy}
+                          className="text-muted-foreground hover:text-destructive"
+                          data-testid="nation-op-reject"
+                        >
+                          <X className="size-3.5" />
+                          Reject
+                        </Button>
+                        <Button
+                          size="sm"
+                          onClick={confirm}
                           disabled={opBusy}
                           data-testid="nation-op-confirm"
                         >
@@ -128,21 +243,57 @@ export default function NationOpDialog({
                       </div>
                     </div>
                   ) : (
-                    <div className="flex items-center justify-between gap-2">
-                      <span className="text-[11px] text-muted-foreground">
-                        {op.kind === 'split' ? 'Split' : 'Merge'} isn’t available yet — dismiss to ignore it.
-                      </span>
-                      <Button
-                        variant="ghost"
-                        size="sm"
-                        onClick={() => onReject(i)}
-                        disabled={opBusy}
-                        className="text-muted-foreground hover:text-destructive"
-                        data-testid="nation-op-reject"
-                      >
-                        <X className="size-3.5" />
-                        Dismiss
-                      </Button>
+                    <div className="space-y-2.5">
+                      <div className="flex flex-wrap gap-1.5">
+                        {(op as { nationRefs: string[] }).nationRefs.map((ref, ri) => {
+                          const isSurvivor = resolveRef(ref) === survivorId;
+                          return (
+                            <Badge
+                              key={ri}
+                              variant={isSurvivor ? 'default' : 'secondary'}
+                              className="text-[11px]"
+                              data-testid="nation-op-input"
+                            >
+                              {name(ref)}
+                              {isSurvivor ? ' (survivor)' : ''}
+                            </Badge>
+                          );
+                        })}
+                      </div>
+                      <Input
+                        value={edits[i] ?? (op as { into: string }).into}
+                        onChange={(e) => setEdits((p) => ({ ...p, [i]: e.target.value }))}
+                        placeholder="New name…"
+                        data-testid="nation-op-name-input"
+                      />
+                      {!mergeValid && (
+                        <p className="text-[11px] text-muted-foreground">
+                          This merge is not valid as proposed — confirming will dismiss it
+                          without changing the world.
+                        </p>
+                      )}
+                      <div className="flex justify-end gap-2">
+                        <Button
+                          variant="ghost"
+                          size="sm"
+                          onClick={() => onReject(i)}
+                          disabled={opBusy}
+                          className="text-muted-foreground hover:text-destructive"
+                          data-testid="nation-op-reject"
+                        >
+                          <X className="size-3.5" />
+                          Reject
+                        </Button>
+                        <Button
+                          size="sm"
+                          onClick={confirm}
+                          disabled={opBusy}
+                          data-testid="nation-op-confirm"
+                        >
+                          {opBusy ? <Loader2 className="size-3.5 animate-spin" /> : <Check className="size-3.5" />}
+                          Confirm
+                        </Button>
+                      </div>
                     </div>
                   )}
                 </li>

src/components/WorldMap.tsx

@@ -10,12 +10,14 @@ import workerUrl from 'maplibre-gl/dist/maplibre-gl-worker.mjs?url';
 maplibregl.setWorkerUrl(workerUrl);
 import {
   mapFeatureOwner,
+  MARKER_TYPE_INFO,
+  nationColor,
   regionFillStyle,
   unownedTooltipLabel,
   type RegionMap,
   type RegionOwner,
 } from '@shared/protocol';
-import type { Nation } from '@shared/types';
+import { MARKER_TYPES, type MapMarker, type Nation } from '@shared/types';
 import { cn } from '@/lib/utils';
 import { idToKey } from '@/lib/regions';
 
@@ -45,8 +47,16 @@ type GeoSource = maplibregl.GeoJSONSource;
 // looked black, and `styledata` was gated on fetching a remote document. An
 // inline object loads instantly, so `isStyleLoaded()` / `styledata` fire
 // immediately and the choropleth is guaranteed to paint. (The OFM `ne2sr`
-// raster has no vector tiles, so no glyphs endpoint is needed — we don't add
-// label layers; the choropleth provides the borders.)
+// raster has no vector tiles, so the basemap itself needs no label layers —
+// the choropleth provides the borders.)
+//
+// No `glyphs` URL: the map needs no MapLibre *text* rendering. The basemap is
+// raster (its labels are baked into the PNG tiles), and the LLM-placed map
+// markers (v0.27, #44) are drawn as canvas-generated icon images in a symbol
+// layer — fully self-contained, so they render offline and deterministically
+// without depending on any external font/glyph endpoint (the OpenFreeMap
+// `fonts/` path is a dead nginx 404, and the basemap's apparent labels come
+// from the raster, not from glyphs).
 const NE2SR_TILES = ['https://tiles.openfreemap.org/natural_earth/ne2sr/{z}/{x}/{y}.png'];
 
 const INLINE_STYLE: maplibregl.StyleSpecification = {
@@ -88,6 +98,8 @@ const PLAYER_LINE = 'player-line';
 const FLASH_LINE = 'flash-line';
 const HOVER_FILL = 'hover-fill';
 const HOVER_LINE = 'hover-line';
+const MARKERS_SOURCE = 'markers';
+const MARKER_SYMBOL = 'markers-symbol';
 
 /** Sensible per-scenario initial camera: Europe for the WWII scenarios, wider for the global ones. */
 function cameraForPreset(presetId: string): { center: [number, number]; zoom: number } {
@@ -195,6 +207,186 @@ function featuresByRegionKeys(
   return { type: 'FeatureCollection', features: JSON.parse(JSON.stringify(features)) };
 }
 
+// --- Map markers (v0.27, #44) ------------------------------------------------
+//
+// The LLM places named point markers (cities, factories, armies, ports,
+// capitals, fleets, rocket sites, gatherings) anchored to a region key. The
+// engine positions each at its region's centroid (deterministic small offset)
+// and recomputes its owner from the region's current owner every turn. The
+// map renders them as a single top-most symbol layer: a per-type glyph
+// character in front of the name, per-type color, dark-theme halo.
+
+/**
+ * The GeoJSON behind the marker symbol layer: one Point per marker at
+ * `[lon, lat]`, carrying the stable id, type, name, its type's glyph, and the
+ * current owner's name + stable color (empty when the region is unowned).
+ * Pure; the caller passes the current marker list + nations record, so a
+ * renamed/removed owner is picked up on the next paint.
+ */
+function buildMarkersFC(markers: MapMarker[], nations: Record<string, Nation>): FeatureCollection {
+  const features = markers.map((m) => {
+    const owner = m.ownerNationId ? nations[m.ownerNationId] : undefined;
+    return {
+      type: 'Feature' as const,
+      geometry: { type: 'Point' as const, coordinates: [m.lon, m.lat] as [number, number] },
+      properties: {
+        id: m.id,
+        type: m.type,
+        name: m.name,
+        glyph: MARKER_TYPE_INFO[m.type]?.glyph ?? '',
+        owner: owner?.name ?? '',
+        ownerId: owner?.id ?? '',
+        ownerColor: owner ? nationColor(owner.id) : '',
+      },
+    };
+  });
+  return { type: 'FeatureCollection', features };
+}
+
+// Small canvas-path helpers for the marker icons (self-contained shapes — no
+// unicode/font dependency, so they render identically in any environment).
+function roundRectPath(
+  ctx: CanvasRenderingContext2D,
+  x: number,
+  y: number,
+  w: number,
+  h: number,
+  r: number,
+): void {
+  ctx.beginPath();
+  ctx.moveTo(x + r, y);
+  ctx.lineTo(x + w - r, y);
+  ctx.quadraticCurveTo(x + w, y, x + w, y + r);
+  ctx.lineTo(x + w, y + h - r);
+  ctx.quadraticCurveTo(x + w, y + h, x + w - r, y + h);
+  ctx.lineTo(x + r, y + h);
+  ctx.quadraticCurveTo(x, y + h, x, y + h - r);
+  ctx.lineTo(x, y + r);
+  ctx.quadraticCurveTo(x, y, x + r, y);
+  ctx.closePath();
+}
+
+function starPath(
+  ctx: CanvasRenderingContext2D,
+  cx: number,
+  cy: number,
+  spikes: number,
+  outer: number,
+  inner: number,
+): void {
+  let rot = (Math.PI / 2) * -1;
+  const step = Math.PI / spikes;
+  ctx.beginPath();
+  ctx.moveTo(cx + Math.cos(rot) * outer, cy + Math.sin(rot) * outer);
+  for (let i = 0; i < spikes; i++) {
+    rot += step;
+    ctx.lineTo(cx + Math.cos(rot) * inner, cy + Math.sin(rot) * inner);
+    rot += step;
+    ctx.lineTo(cx + Math.cos(rot) * outer, cy + Math.sin(rot) * outer);
+  }
+  ctx.closePath();
+}
+
+/**
+ * (v0.27, #44) Draw one marker-type icon into an offscreen canvas: a distinct
+ * shape per type, filled with the type's color from the shared
+ * `MARKER_TYPE_INFO` contract, with a dark outline for legibility on any
+ * choropleth fill. Added to the map as a named image and referenced by the
+ * symbol layer's `icon-image` — a real symbol layer, per-type color + form,
+ * with zero external font/glyph dependency.
+ */
+function drawMarkerIcon(type: MapMarker['type']): ImageData {
+  const S = 44;
+  const c = document.createElement('canvas');
+  c.width = S;
+  c.height = S;
+  const ctx = c.getContext('2d')!;
+  const cx = S / 2;
+  const cy = S / 2;
+  ctx.fillStyle = MARKER_TYPE_INFO[type]?.color ?? '#cbd5e1';
+  ctx.strokeStyle = '#0b1220';
+  ctx.lineWidth = 2.5;
+  ctx.lineJoin = 'round';
+  switch (type) {
+    case 'city':
+      ctx.beginPath();
+      ctx.arc(cx, cy, S * 0.3, 0, Math.PI * 2);
+      break;
+    case 'factory': {
+      const h = S * 0.5;
+      roundRectPath(ctx, cx - h / 2, cy - h / 2, h, h, 5);
+      break;
+    }
+    case 'army': {
+      const r = S * 0.34;
+      ctx.beginPath();
+      ctx.moveTo(cx, cy - r);
+      ctx.lineTo(cx + r, cy + r * 0.8);
+      ctx.lineTo(cx - r, cy + r * 0.8);
+      ctx.closePath();
+      break;
+    }
+    case 'port': {
+      const r = S * 0.36;
+      ctx.beginPath();
+      ctx.moveTo(cx, cy - r);
+      ctx.lineTo(cx + r, cy);
+      ctx.lineTo(cx, cy + r);
+      ctx.lineTo(cx - r, cy);
+      ctx.closePath();
+      break;
+    }
+    case 'capital':
+      starPath(ctx, cx, cy, 5, S * 0.36, S * 0.15);
+      break;
+    case 'fleet':
+    case 'gathering':
+      ctx.beginPath();
+      ctx.arc(cx, cy, S * 0.32, 0, Math.PI * 2);
+      break;
+    case 'rocket': {
+      const w = S * 0.14;
+      ctx.beginPath();
+      ctx.moveTo(cx, cy - S * 0.36);
+      ctx.lineTo(cx + S * 0.22, cy - S * 0.04);
+      ctx.lineTo(cx + w, cy - S * 0.04);
+      ctx.lineTo(cx + w, cy + S * 0.34);
+      ctx.lineTo(cx - w, cy + S * 0.34);
+      ctx.lineTo(cx - w, cy - S * 0.04);
+      ctx.lineTo(cx - S * 0.22, cy - S * 0.04);
+      ctx.closePath();
+      break;
+    }
+  }
+  ctx.fill();
+  ctx.stroke();
+  // fleet and gathering share a circle base; an inner mark tells them apart
+  // (fleet = a dark porthole dot, gathering = a white bullseye dot).
+  if (type === 'fleet' || type === 'gathering') {
+    ctx.beginPath();
+    ctx.arc(cx, cy, S * 0.13, 0, Math.PI * 2);
+    ctx.fillStyle = type === 'fleet' ? '#0b1220' : '#ffffff';
+    ctx.fill();
+  }
+  // Hand MapLibre the raw pixels (an untainted canvas, so getImageData is safe)
+  // rather than the canvas element — `addImage` accepts ImageData directly.
+  return ctx.getImageData(0, 0, S, S);
+}
+
+/** The hover tooltip for a marker: its type label + name, then the owner chip. */
+function markerTooltipHtml(
+  type: string,
+  name: string,
+  owner: string,
+  ownerColor: string,
+): string {
+  const label = MARKER_TYPE_INFO[type as MapMarker['type']]?.label ?? 'Marker';
+  const ownerLine = owner
+    ? `<div class="hm-popup-owner"><span class="hm-chip" style="background:${ownerColor}"></span>${esc(owner)}</div>`
+    : '<div class="hm-popup-sub">No owner</div>';
+  return `<div class="hm-popup"><div class="hm-popup-title">${esc(label)}: ${esc(name)}</div>${ownerLine}</div>`;
+}
+
 const esc = (s: string) =>
   s.replace(/[&<>"']/g, (c) => ({ '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' }[c] as string));
 
@@ -254,6 +446,13 @@ interface Props {
    * component doc for the full behavior.
    */
   onFocusNation?: (id: string, info?: { name?: string }) => void;
+  /**
+   * (v0.27, #44) The game's named map markers (`GameState.markers`): the LLM
+   * places/removes them over time, the engine positions each at its region's
+   * centroid and keeps its owner in sync with the region's owner. Rendered as
+   * a top-most symbol layer (per-type glyph + name, per-type color).
+   */
+  markers?: MapMarker[];
 }
 
 /**
@@ -286,6 +485,18 @@ interface Props {
  * a plain "No owner" sub-line. The colors/labels come from the shared
  * `regionFillStyle` / `unownedTooltipLabel` contract in @shared/protocol.
  *
+ * (v0.27, #44) LLM-placed **map markers** (`markers` prop = `GameState.markers`)
+ * render on a top-most symbol layer: each is its type's canvas-generated icon
+ * (a distinct shape, per-type color from the shared `MARKER_TYPE_INFO`
+ * contract, dark-outlined) at the engine-derived position (region centroid +
+ * small deterministic offset). The icons are drawn into named map images
+ * (`marker-<type>`), so there is no external font/glyph dependency and markers
+ * render offline and deterministically. Hovering a marker shows a tooltip
+ * (type label + name + owner chip); clicking one switches the dossier to the
+ * owning nation (no-op when the marker's region is unowned). The region
+ * hover/click handlers detect a marker under the cursor (MapLibre layer events
+ * have no propagation) and act on the marker's data.
+ *
  * Zoom and pan are driven directly by the user (MapLibre wheel/trackpad + drag)
  * — no floating control and no external API.
  */
@@ -297,6 +508,7 @@ export default function WorldMap({
   className,
   unowned,
   onFocusNation,
+  markers,
 }: Props) {
   const containerRef = useRef<HTMLDivElement>(null);
   const mapRef = useRef<maplibregl.Map | null>(null);
@@ -311,12 +523,14 @@ export default function WorldMap({
   const presetRef = useRef(presetId);
   const unownedRef = useRef<Set<string>>(new Set(unowned ?? []));
   const onFocusNationRef = useRef(onFocusNation);
+  const markersRef = useRef<MapMarker[]>(markers ?? []);
   regionsRef.current = regions;
   nationsRef.current = nations;
   playerRef.current = playerNationId;
   presetRef.current = presetId;
   unownedRef.current = new Set(unowned ?? []);
   onFocusNationRef.current = onFocusNation;
+  markersRef.current = markers ?? [];
 
   // Diffing state for the transient territory-change flash (owned by this component
   // so a resync with identical data never re-flashes).
@@ -424,6 +638,39 @@ export default function WorldMap({
     const onHover = (e: maplibregl.MapLayerMouseEvent) => {
       const f = e.features?.[0];
       if (!f) return;
+      // (v0.27, #44) A marker rendered on top of this region wins the hover.
+      // The region polygon is always beneath a marker, so this FILL_LAYER
+      // delegate fires in both cases; if a marker icon is under the cursor,
+      // show the marker's tooltip (name + type + owner) instead of the
+      // region's. `e.point` is the cursor's pixel position, so querying the
+      // marker layer there tests the icon's (small) hit area, not the whole
+      // region.
+      const markerHits = map.queryRenderedFeatures(e.point, { layers: [MARKER_SYMBOL] });
+      if (markerHits.length > 0) {
+        const mp = (markerHits[0].properties ?? {}) as {
+          type?: string;
+          name?: string;
+          owner?: string;
+          ownerColor?: string;
+        };
+        hoverPopup
+          .setLngLat(e.lngLat)
+          .setHTML(
+            markerTooltipHtml(
+              typeof mp.type === 'string' ? mp.type : '',
+              typeof mp.name === 'string' ? mp.name : '',
+              typeof mp.owner === 'string' ? mp.owner : '',
+              typeof mp.ownerColor === 'string' ? mp.ownerColor : '',
+            ),
+          )
+          .addTo(map);
+        map.getCanvas().style.cursor = 'pointer';
+        // A marker has no region outline to highlight; clear the previous one
+        // (and reset lastHoverId so moving back onto a region re-triggers it).
+        lastHoverId = null;
+        (map.getSource(HOVER_SOURCE) as GeoSource | undefined)?.setData(emptyFC());
+        return;
+      }
       const p = f.properties as { name?: string; regionId?: string };
       const subId = typeof p?.regionId === 'string' ? p.regionId : '';
       if (subId && subId !== lastHoverId) {
@@ -466,6 +713,19 @@ export default function WorldMap({
     const onClick = (e: maplibregl.MapLayerMouseEvent) => {
       const f = e.features?.[0];
       if (!f) return;
+      // (v0.27, #44) A marker under the cursor: focus its owning nation
+      // (identical to its region's owner — the engine keeps a marker's owner in
+      // sync with the region) and carry the marker's name into the dossier.
+      const markerHits = map.queryRenderedFeatures(e.point, { layers: [MARKER_SYMBOL] });
+      if (markerHits.length > 0) {
+        const mp = (markerHits[0].properties ?? {}) as { ownerId?: string; name?: string };
+        const owner = typeof mp.ownerId === 'string' ? mp.ownerId : '';
+        if (owner) {
+          const info = typeof mp.name === 'string' ? { name: mp.name } : undefined;
+          onFocusNationRef.current?.(owner, info);
+        }
+        return;
+      }
       const region = mapFeatureOwner(regionsRef.current, f);
       if (!region?.ownerId) return;
       // Carry the clicked sub-region's name so the dossier can show which region
@@ -497,6 +757,9 @@ export default function WorldMap({
       if (!map.getSource(FLASH_SOURCE)) {
         map.addSource(FLASH_SOURCE, { type: 'geojson', data: emptyFC() });
       }
+      if (!map.getSource(MARKERS_SOURCE)) {
+        map.addSource(MARKERS_SOURCE, { type: 'geojson', data: emptyFC() });
+      }
     };
 
     // Stamp ownership + colors onto the regions source (no-op until both the
@@ -509,6 +772,26 @@ export default function WorldMap({
       src.setData(applyRegions(geo, regionsRef.current, playerRef.current, idKey, unownedRef.current));
     };
 
+    // Stamp the current markers onto the marker source (v0.27, #44).
+    const paintMarkers = () => {
+      const src = map.getSource(MARKERS_SOURCE) as GeoSource | undefined;
+      if (!src) return;
+      src.setData(buildMarkersFC(markersRef.current, nationsRef.current));
+    };
+
+    // Register the eight canvas-generated marker-type icon images (v0.27, #44).
+    // Images are cleared on a style (re)load, so this is (re)run from
+    // `ensureLayers` (which fires on every `styledata`). Self-contained — no
+    // external font/glyph endpoint — so markers render offline and
+    // deterministically.
+    const ensureMarkerImages = async () => {
+      for (const type of MARKER_TYPES) {
+        const id = `marker-${type}`;
+        if (map.getImage(id)) continue;
+        await map.addImage(id, drawMarkerIcon(type));
+      }
+    };
+
     const ensureLayers = async () => {
       if (cancelled) return;
       ensureSources();
@@ -528,6 +811,7 @@ export default function WorldMap({
       }
       if (cancelled) return;
       paintRegions();
+      paintMarkers();
       if (!map.getLayer(FILL_LAYER)) {
         // The choropleth is the star: a high opacity so the vivid per-nation
         // colors read clearly even on the dark background / over the terrain.
@@ -554,8 +838,9 @@ export default function WorldMap({
       }
       // NOTE: layers are added in bottom→top order (each appends on top). The
       // stack is: fill, base borders, player border, territory-change flash,
-      // hover brighten, hover outline. Do not use a `beforeId` here — it throws
-      // if that layer does not exist yet on a fresh style load.
+      // hover brighten, hover outline, and (top-most) the LLM-placed map
+      // markers' symbol layer (v0.27, #44). Do not use a `beforeId` here — it
+      // throws if that layer does not exist yet on a fresh style load.
       if (!map.getLayer(PLAYER_LINE)) {
         map.addLayer({
           id: PLAYER_LINE,
@@ -589,6 +874,36 @@ export default function WorldMap({
           paint: { 'line-color': '#ffffff', 'line-width': 1.6, 'line-opacity': 0.9 },
         });
       }
+      // (v0.27, #44) The LLM-placed map markers: a top-most symbol layer.
+      // Each marker renders its type's canvas-generated icon (a distinct shape,
+      // per-type color from the shared MARKER_TYPE_INFO contract) with a dark
+      // outline for legibility on any choropleth fill. The icon images are
+      // self-contained (no external font/glyph endpoint), so markers render
+      // offline and deterministically. `icon-image` is `marker-<type>`, the
+      // named canvas images registered by `ensureMarkerImages` above.
+      await ensureMarkerImages();
+      if (!map.getLayer(MARKER_SYMBOL)) {
+        map.addLayer({
+          id: MARKER_SYMBOL,
+          type: 'symbol',
+          source: MARKERS_SOURCE,
+          layout: {
+            'icon-image': ['concat', 'marker-', ['get', 'type']],
+            'icon-size': 0.8,
+            'icon-allow-overlap': true,
+            'icon-ignore-placement': true,
+          },
+        });
+      }
+      // Marker interactions: the markers sit above the choropleth, but they
+      // deliberately share the region (FILL_LAYER) handlers registered below.
+      // MapLibre layer-scoped events are independent per-layer delegates (no
+      // propagation, no stopPropagation), so a marker-on-region would fire
+      // both a marker and a region handler. Instead the region handlers detect
+      // a marker under the cursor (see onHover/onClick) and act on the
+      // marker's data; clicking a marker focuses its owning nation via the
+      // same path as clicking its region (the marker's owner == its region's
+      // owner).
       map.off('mousemove', FILL_LAYER, onHover);
       map.off('mouseout', FILL_LAYER, onHoverOut);
       map.off('click', FILL_LAYER, onClick);
@@ -646,6 +961,19 @@ export default function WorldMap({
     }
   }, [regions, playerNationId, unowned]);
 
+  // (v0.27, #44) Repaint the marker symbol layer whenever the marker list
+  // changes (a turn placed/removed markers) or the nations record changes
+  // (a confirmed rename/merge changes an owner's display name). No-op until
+  // the map + source exist (the mount effect's ensureLayers applies the
+  // current data once the layer structure is in place).
+  useEffect(() => {
+    const map = mapRef.current;
+    if (!map) return;
+    const src = map.getSource(MARKERS_SOURCE) as GeoSource | undefined;
+    if (!src) return;
+    src.setData(buildMarkersFC(markers ?? [], nations));
+  }, [markers, nations]);
+
   // Full-viewport, edge-to-edge background layer. `position: fixed` is set
   // inline because MapLibre's own stylesheet sets `.maplibregl-map` to
   // `position: relative`, which would otherwise win over a Tailwind class.

src/lib/api.ts

@@ -62,10 +62,13 @@ export const api = {
       method: 'POST',
       body: JSON.stringify({ index }),
     }),
-  // (v0.23, #16 P4a) Confirm a pending nation-op proposal by its index in
-  // `game.pendingNationOps` (a rename takes effect; `edits.name` overrides the
-  // proposed name). Fast, non-LLM — no turn advance. Returns the updated game.
-  confirmNationOp: (id: string, index: number, edits?: { name?: string }) =>
+  // (v0.23, #16 P4a; v0.24, #16 P4b) Confirm a pending nation-op proposal by
+  // its index in `game.pendingNationOps`: a rename takes effect (`edits.name`
+  // overrides the proposed name), a split partitions the nation's territory
+  // (`edits.playerPart` picks which part the player leads, default 0), and a
+  // merge folds its inputs into the survivor (`edits.name` overrides the
+  // merged name). Fast, non-LLM — no turn advance. Returns the updated game.
+  confirmNationOp: (id: string, index: number, edits?: { name?: string; playerPart?: number }) =>
     req<ConfirmNationOpResponse>(`/api/games/${id}/nation-op/confirm`, {
       method: 'POST',
       body: JSON.stringify({ index, ...(edits ? { edits } : {}) }),