Fix annotation height culling review findings (#1277)

- Restrict the conservative frustum test to height sampling only: an
  endpoint outside it still projects at its cached or zero height, so an
  arrow with one off-frustum endpoint keeps its visible connector and label.
- Test a settled height as the actual point; reject an unknown height
  before sampling only when both ends of the accepted -430..9000 m range
  fail the same constraint (behind camera, or below horizon), which the
  convexity of each rejection region makes a proof for the whole range.
- Queue keys refused by an exhausted budget and reserve the next pass's
  budget for the oldest of them, so anchors beyond the first 32 are served
  under sparse passes while keeping 32 samples per pass and 1 s retries.
- Add regressions with a real frustum, a low-angle authored camera, and
  33 persistent points under sparse passes; consolidate CURRENT-STATE.

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

docs/CURRENT-STATE.md

@@ -9,7 +9,15 @@ broader suffix variants. Follow-ups retain boundary provenance, and cancelled
 lookups preserve the previous analyst cohort and boundary source. Navigation
 search keeps a successful geocode, with no search or view-based region recovery.
 
-Screen annotations reject hidden records and anchors wholly behind the camera or globe horizon before surface sampling. Unresolved visible heights share a 32-sample projection-pass budget, retry at most once per second per anchor on rendered frames, and retain no extra timer or listener. Unsettled points continue retrying as late terrain arrives; behind-camera, horizon and conservative frustum culls run before sampling. Validated heights remain settled in the bounded cache.
+Screen annotations skip hidden records and, before surface sampling, reject an
+unsettled anchor only when its whole accepted height range (-430 to 9000 m) is
+behind the camera or below the globe horizon; a settled height is tested as the
+actual point. Anchors outside the conservative frustum still project at their
+cached or zero height, so a partly visible arrow keeps its connector, but do
+not sample. Unresolved visible heights share a 32-sample projection-pass budget,
+served oldest-refused first, retry at most once per second per anchor on
+rendered frames, and retain no extra timer or listener. Validated heights remain
+settled in the bounded cache.
 
 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