Cut the Google requests the HUD summary makes on its own

The HUD builds place context for its AI summary whenever the camera
settles, and each build paid for up to four reverse geocodes plus a Nearby
Places search, even when no OpenAI key was configured to use them.

- Ask GET /api/openai/hud-summary/status once; with no summary configured,
  or after an unconfigured reply, make no place lookups for the page.
- Reverse-geocode at most two points: the view center and one viewport
  point.
- Reuse a lookup until the view center moves a quarter of the visible
  width, the camera's distance to it doubles or halves, or the camera
  crosses a lookup height. The reused points are asked again, so only a
  timeout, failure or empty answer spends.
- Repaint the last AI reply when a small pan leaves the context unchanged.

Cached-only hosts and voice context lookups are unchanged.

src/voice/gevActions.js

@@ -12,6 +12,11 @@ import { msg } from '../i18n/index.js';
 import * as Cesium from 'cesium';
 import { CITY_POIS } from '../cityPois.js';
 import { greatCircleKm } from '../geoDistance.js';
+import {
+  hudViewportSamples,
+  placeLookupView,
+  placeLookupViewChanged,
+} from '../hudPlaceLookup.js';
 import {
   findPoiByName,
   flyToGlobeView,
@@ -2692,13 +2697,20 @@ function runManagedVoiceNavigation(
   };
 }
 
+/**
+ * Place labels for the HUD's passive summary. It geocodes the view center
+ * and one more point. While the view still shows about the same area (see
+ * hudPlaceLookup.js) it answers for the points the last lookup asked about
+ * instead, so a settled camera does not buy a new set of Google requests for
+ * every small pan; those points are cache hits, and only what the last
+ * lookup did not get (a timeout, a failure, an empty answer) is asked again.
+ * `cachedOnly` reads the shared caches and makes no request.
+ */
 export async function getBasemapLabelContext(
   viewer,
   service = defaultGeospatial,
-  { cachedOnly = false } = {},
+  { cachedOnly = false, previous = null } = {},
 ) {
-  const { reverseGeocodeCache, nearbyPlacesCache } = cachesFor(service);
-  const samples = sampleViewportCartographics(viewer);
   const cameraHeightM = viewer.camera.positionCartographic.height;
   const target = getViewTargetCartographic(viewer);
   if (!target) {
@@ -2706,11 +2718,77 @@ export async function getBasemapLabelContext(
       placeLabels: [],
       streetLabels: [],
       nearbyPlaceLabels: [],
+      view: null,
+      lookup: null,
     };
   }
 
   const latitude = Number(Cesium.Math.toDegrees(target.latitude).toFixed(6));
   const longitude = Number(Cesium.Math.toDegrees(target.longitude).toFixed(6));
+  const view = placeLookupView({
+    latitude,
+    longitude,
+    rangeM: viewTargetRangeM(viewer, target, cameraHeightM),
+    fovRad: viewer.camera.frustum?.fov,
+    aspectRatio: viewer.camera.frustum?.aspectRatio,
+    tier: basemapLookupTier(cameraHeightM),
+  });
+  if (
+    !cachedOnly &&
+    previous?.lookup &&
+    !placeLookupViewChanged(previous.view, view)
+  ) {
+    // The same points again: what the last lookup got is a cache hit, and
+    // only what it did not (a timeout, a failure, an empty answer) is asked.
+    const labels = await basemapLabelsAt(previous.lookup, service, {
+      cachedOnly: false,
+    });
+    return { ...labels, view: previous.view, lookup: previous.lookup };
+  }
+  const samples = sampleViewportCartographics(viewer);
+  const lookup = {
+    latitude,
+    longitude,
+    cameraHeightM,
+    // Cache reads are free, so a cached-only host keeps every sample.
+    samples: cachedOnly
+      ? samples
+      : hudViewportSamples(samples, shouldReverseGeocode(cameraHeightM)),
+  };
+  return {
+    ...(await basemapLabelsAt(lookup, service, { cachedOnly })),
+    view,
+    lookup,
+  };
+}
+
+/** Which of the height-gated lookups a camera height calls for. */
+function basemapLookupTier(cameraHeightM) {
+  return [
+    shouldReverseGeocode(cameraHeightM),
+    shouldReverseGeocodeViewport(cameraHeightM) && cameraHeightM > 10000,
+    shouldFetchNearbyPlaces(cameraHeightM) &&
+      nearbyPlacesRadiusM(cameraHeightM),
+  ].join(':');
+}
+
+/** Camera distance to the view target, or the camera height without one. */
+function viewTargetRangeM(viewer, target, cameraHeightM) {
+  const position = viewer.camera.positionWC;
+  if (!position) return cameraHeightM;
+  const range = Cesium.Cartesian3.distance(
+    position,
+    Cesium.Cartographic.toCartesian(target),
+  );
+  return Number.isFinite(range) ? range : cameraHeightM;
+}
+
+async function basemapLabelsAt(
+  { latitude, longitude, cameraHeightM, samples },
+  service,
+  { cachedOnly },
+) {
+  const { reverseGeocodeCache, nearbyPlacesCache } = cachesFor(service);
   const cachedViewportPlaces = viewportPlacesFromCache(
     samples,
     cameraHeightM,
@@ -2748,7 +2826,6 @@ export async function getBasemapLabelContext(
     resolveWithin(placePromise, BASEMAP_CONTEXT_WAIT_MS, null),
     resolveWithin(nearbyPromise, BASEMAP_CONTEXT_WAIT_MS, []),
   ]);
-
   return {
     placeLabels: uniqueStrings([
       place?.formattedAddress,