fix(terrain): reject out-of-range points at the proxy boundary

Rebased onto current main with review follow-ups folded in.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -1192,6 +1192,10 @@ The browser layers and their rendering remain in their existing modules.
 
 ## Terrain height cache bound
 
+The terrain proxy parser rejects finite longitudes outside [-180, 180] and
+latitudes outside [-90, 90] for every client before upstream resolution. One
+out-of-range point rejects the whole batch; inclusive WGS84 bounds remain valid.
+
 The client terrain-height resolver's in-memory cache is bounded at 20 000
 entries (`DEFAULT_MAX_CACHE_ENTRIES`, overridable per instance through
 `createTerrainHeights({ maxCacheEntries })`). Coordinate rounding makes repeated