v0.27.0 (#44): LLM-placed named map point markers

- 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).

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 +15,8 @@
 //   - 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)
 //
 // 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 +43,15 @@ 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 }>;
 }
 
 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 +59,10 @@ 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 +71,7 @@ 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 base = [
     path.join(root, 'public'), // dev: Vite serves public/ at /
     path.join(root, 'dist'), // prod: Vite copies public/* -> dist/ (== clientDir)
@@ -105,7 +116,38 @@ 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 = {};
+      }
+    }
+
+    data = { idToKey, keyToInfo, keysByCountry, validKeys, adjacency, centroids };
     return validKeys.size > 0;
   } catch (err) {
     console.error('[regions] failed to load region data', err);
@@ -189,6 +231,27 @@ 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;
+}
+
+/**
+ * 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 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