fix(street-level): sequence loads, playback and nearest-photo edge cases

From gekh's review of #768, each bug with a test that fails before:

- P2: a failed sequence load clears the previous sequence's cones, resets
  the selection and can be retried; a second click while loading starts no
  second lookup. sequences.js had no tests: sequences.test.mjs now covers
  failure and retry, a superseded late answer, the cache and clearSelection.
- P2: closing a photo stops MapillaryJS sequence playback, which kept the
  hidden viewer stepping and downloading images.
- openNearest without the panel reports it instead of loading forever, and
  stops if the layer (or its provider) went off during the lookup; the
  mesh sampler's misses are bounded and forgotten with its samples; the
  sequence count is the union of ids across tiles; a provider withdraws
  only its own error, so a sequence error cannot mask KEY REJECTED; hover
  stays on (throttled) under an orbiting camera and re-picks when it
  stops; "since N days" follows the clock in a long-open tab.
- A prewarm waits for one in flight and then builds if it gave up.
- New coverage for the layer core (credits, KEY REJECTED vs REQUIRED,
  switching a provider off), the refresh wiring of the tilted-view fix and
  the draped-to-cast swap completion.
- Cleanup: loading is derived from pending; freshStreet(); tile ranking
  computes distances once and shares one path for the date line; shared
  metresBetween / whenIdle / redrawTile; one NEAREST_RADIUS_M and one
  source method list; unused contract fields, exports, getImage and the
  decoder's image branch removed; PROVIDER_COLORS lists only Mapillary.

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

src/layers/streetLevel/viewerHost.js

@@ -1,3 +1,5 @@
+import { freshStreet } from './state.js';
+
 /**
  * Own the one viewer element in the panel and whichever provider's viewer
  * adapter is mounted in it. Poses the adapter emits become `state.street`,
@@ -107,16 +109,20 @@ export function createViewerHost({ state, parts }) {
   }
 
   /**
-   * Open an image from one provider. Returns once the first pose is in;
-   * later poses stream through `state.street` as the user navigates.
+   * Open an image from one provider. Resolves once the first pose is in
+   * (true) or the open failed or was overtaken (false); later poses stream
+   * through `state.street` as the user navigates.
+   * @returns {Promise<boolean>}
    */
   async function open(providerId, imageId, { frame = true } = {}) {
     const entry = providerEntry(providerId);
-    if (!entry || !imageId) return;
+    if (!entry || !imageId) return false;
     if (!state.street.host) {
+      // A nearest-image lookup may have set it; nothing is loading now.
+      state.street.loading = false;
       state.street.error = 'Open the Street Level panel to view imagery';
       notify();
-      return;
+      return false;
     }
     const seq = ++openSeq;
     const current = () => seq === openSeq;
@@ -131,9 +137,9 @@ export function createViewerHost({ state, parts }) {
     notify();
     try {
       const adapter = await mount(entry);
-      if (!current()) return;
+      if (!current()) return false;
       await adapter.open(String(imageId));
-      if (!current()) return;
+      if (!current()) return false;
       if (frame && !state.street.follow) parts.follow.lookAtPosition();
     } catch (error) {
       if (current())
@@ -142,32 +148,16 @@ export function createViewerHost({ state, parts }) {
       if (current()) state.street.loading = false;
       notify();
     }
-    if (current() && !state.street.error) selectCurrentSequence();
+    if (!current() || state.street.error) return false;
+    selectCurrentSequence();
+    return true;
   }
 
   /** Close the image; the mounted adapter stays warm for the next open. */
   function close() {
     openSeq++;
     active?.adapter.close();
-    Object.assign(state.street, {
-      open: false,
-      follow: false,
-      providerId: null,
-      providerName: null,
-      providerLabel: null,
-      imageId: null,
-      position: null,
-      bearing: null,
-      tilt: null,
-      altitude: null,
-      isPano: false,
-      capturedAt: null,
-      sequenceId: null,
-      creator: null,
-      externalUrl: null,
-      loading: false,
-      error: null,
-    });
+    Object.assign(state.street, freshStreet());
     parts.marker.clear();
     notify();
   }
@@ -248,6 +238,5 @@ export function createViewerHost({ state, parts }) {
     setRenderMode,
     prewarm,
     unmount,
-    activeProviderId: () => active?.id || null,
   };
 }