cache derived geometry: merged road chains + settlement list persisted with cell fingerprints; two-tier best-first road stitching (raw-node headings, permissive interchange pass); fast path skips all raw parsing on unchanged data

README.md

@@ -30,8 +30,7 @@ real terrain, driven by the real sun, moon, stars, and live weather.
   mood (sunny / cloudy / stormy / night).
 - **Fully cached, offline-capable**: basemap tiles, elevation grid,
   Overpass road/place data, star catalogue and the last weather payload
-  live permanently in IndexedDB. Once warm, the scene renders fully
-  offline; a configurable expiry (`CONFIG.tiles.expireDays`) can refresh
+  live permanently in IndexedDB. Once warm, the scene renders fully offline, and a 15-minute cycle transparently retries anything that previously failed. Merged road chains and the decoded settlement list are cached as well and only recomputed when an Overpass cell is actually re-fetched.tiles.expireDays`) can refresh
   basemap tiles periodically.
 - **Location-aware**: set `CONFIG.location.lat/lon`; everything
   (flight anchor, terrain tiles, sun/moon, weather, star rotation) is