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).

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`,
+);