fix(terrain): keep cold height requests within the browser deadline (#348)

Use 64-point browser and upstream terrain batches to reduce cold-cache timeouts. Preserve successful chunk results, distinguish absent readings from malformed responses, and reject fabricated zero heights.

Original terrain resilience contribution by ItzDESTAQ, with browser batching, validation and regression follow-up by Sameh Khamis.

Validated with unit/build/format/boundary checks, 108 tracking checks, 5 terrain-outage checks, controlled slow-upstream comparison and live browser checks.

Co-authored-by: ItzDESTAQ <[email protected]>
Co-authored-by: Sameh Khamis <[email protected]>

CHANGELOG.md

@@ -63,6 +63,14 @@ of current runtime behavior, see [`docs/CURRENT-STATE.md`](docs/CURRENT-STATE.md
 
 ### Fixed
 
+- Reduce terrain-height timeouts when Re:Earth slows down. Batches are
+  sized against measured response latency on both browser and server to reduce
+  request timeouts, and a partial upstream failure now
+  keeps the heights that did resolve rather than discarding them. A position
+  the upstream answers with no height is reported as an absent reading instead
+  of a failed refresh, so the log distinguishes a slow or broken upstream from
+  one that simply has no value for a coordinate.
+
 - Separate optional Google server credentials for Places and Street View from
   the browser key, contributed by Tom-Neverwinter (#110). Provider Settings,
   Pinokio's app-specific credential handling and setup diagnostics recognize