v0.28.0 (#46): per-region stats — area×population-weighted-median Nation.stats (PR 1 of 2)

CHANGELOG.md

@@ -2,6 +2,30 @@
 
 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 }`.