fix(terrain): bound each height request to one upstream chunk

docs/CURRENT-STATE.md

@@ -1,5 +1,10 @@
 # God's Eye View Current State
 
+Terrain height requests accept at most 64 points, matching the browser service's
+existing batch size and one bounded upstream chunk. Larger requests return HTTP
+413 before disk-cache loading or upstream work; malformed coordinates remain 400.
+The browser continues to split larger workloads into sequential 64-point requests.
+
 Shared distance checks use `src/geoDistance.js` with `{ lat, lon }` points and
 the IUGG mean spherical Earth radius, 6371.0088 km. `greatCircleKm` is
 canonical; `greatCircleMeters` is its exact metre conversion. Missing,