Clean up holes/gaps in sub-national regions (v0.15.0)

Part of #16

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 All notable changes to **History** are listed here, newest first.
 
+## v0.15.0 — 2026-10-12 13:49
+- **Filled the small holes left by the v0.14 coarsening (Part of #16).** The coarsened `public/regions.geo.json` still carried **2,245 tiny enclosed holes** (all < 500 km² in practice) — unfilled patches left by the boolean dissolves and Natural Earth's own digitization, which showed up as "holes in regions". The new `scripts/cleanup-regions.mjs` (`npm run cleanup:regions`) drops every inner ring smaller than the 1,000 km² threshold so each region becomes solid: across **498 features, 56,484 km²** of artifact area was filled, removing the visible unfilled dots.
+- **Real water is kept, not erased.** Any enclosed hole ≥ 1,000 km² survives as a hole. In this dataset the genuinely large lakes (the Great Lakes, the Caspian, the Aral, Lake Superior) had already been dissolved by the v0.14 coarsening, so none remain to preserve; the only surviving hole is a single medium one — **KZ-KZY (Kyzylorda, Kazakhstan) at 5,858 km²**, a real water body in the Aral basin — which is kept. The 1,000 km² threshold sits comfortably between the tiny artifacts (all < 500) and any genuine lake, so it fills exactly the artifacts and nothing else.
+- **The dataset contract is untouched.** Still **1,796 regions** with identical `id`s / `properties.name` / `properties.parent` (0 mismatches), all **177 countries** still covered, the ~100 km floor and the island exemption intact — only inner rings were dropped, never a feature or its identity. The file shrinks 2,431 → **2,249 KB (2.20 MB)** (fewer inner rings).
+- **Deterministic + idempotent.** Fixed threshold, deterministic planar geometry, 4-dp rounding; re-running on the cleaned file rewrites a byte-identical file (sha256-verified). Bridging very-close MultiPolygon parts is available behind an opt-in `--bridge` flag but is **off by default**, because the union it performs can itself mint new medium-sized holes — counter to the fill-holes goal — so the shipped run is the clean hole-fill only.
+- **Tests.** `scripts/regions.test.ts` gains a seventh test asserting that no enclosed hole below the cleanup threshold remains and that only a handful of real water bodies survive (57 tests total). `public/regions.geo.json` and the built `dist/regions.geo.json` are sha256-identical.
+- Part of #16.
+
 ## v0.14.0 — 2026-10-12 09:51
 - **Coarsened the sub-national choropleth dataset to a ~100 km floor (Part of #16).** `public/regions.geo.json` shrinks from 4,138 real administrative regions to **1,796** (2,342 merges): every region smaller than ~100×100 km (10,000 km²) that has a same-country neighbor within 0.2° (≈22 km) of its bounding box is **dissolved into its nearest such neighbor** (nearest by centroid distance; ties → larger area, then id). Standalone cities and micro-districts collapse into the region around them: `US-DC` (191 km²) into Maryland, `FR-75` Paris (59 km²) into Hauts-de-Seine, the UK's 232 admin-1 districts down to **16** regions, and all of North Macedonia's 85 municipalities into one whole-country region.
 - **Islands are exempt.** A region with no same-country neighbor within 0.2° keeps its shape whatever its size — **83** such small islands survive in the final set (Corsica, the Kerguelen/Crozet archipelagos, the Bahamas districts, Lord Howe, …) and the coarsening's fixed point leaves **0** non-island regions below the floor.