fix(street-level): review round — safer docking, mount retry, provider fallthrough

- Only a user's own collapse docks a floating window; cockpit entry,
  restores and the Cyber accordion no longer dock it or delete its saved
  place, and the accordion leaves floating windows alone.
- The viewer host records an adapter as active only after its mount
  succeeds, so a library that failed to load once is retried; concurrent
  opens share one mount, and unmounting mid-mount leaves nothing active.
- openNearest tries every active provider; one provider's error (no key,
  offline) no longer hides the others' imagery.
- The SINCE readout shows its cut-off date as soon as the committed value
  matches the thumb, even while the slider keeps focus.
- A floating window that was only dragged is bounded to the viewport and
  scrolls instead of running off-screen.
- getStats summarises coverage (summarizeCoverage) instead of building a
  full UI snapshot every second; disable() uses credits.hideAll(); smaller
  cleanups in the viewer host and sequence snapshot.
- Unit tests: panel docking and header double press, viewer-host mount
  retry/sharing/cancel, coverage summary.

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

src/layers/streetLevel/uiState.js

@@ -16,6 +16,23 @@ import { COLORS } from './policy.js';
  * @property {Array<{key: string, label: string, color: string}>} legend
  */
 
+/**
+ * What the switched-on providers add up to: summed counts, any loading, the
+ * first hint and error, and whether every one of them lacks its key.
+ * @param {Array<ProviderSnapshot>} providers
+ */
+export function summarizeCoverage(providers) {
+  const active = providers.filter((p) => p.on);
+  return {
+    count: active.reduce((sum, p) => sum + (p.count || 0), 0),
+    loading: active.some((p) => p.loading),
+    hint: active.find((p) => p.hint)?.hint || '',
+    error: active.find((p) => p.error)?.error || null,
+    keyRequired:
+      active.length > 0 && active.every((p) => p.keyRequired === true),
+  };
+}
+
 /**
  * Compose the snapshot the panel renders from the core state and one
  * snapshot per registered provider. Pure, so the merge rules are testable:
@@ -33,8 +50,7 @@ export function composeUIState({
   sequence,
 }) {
   const active = providers.filter((p) => p.on);
-  const keyRequired =
-    active.length > 0 && active.every((p) => p.keyRequired === true);
+  const { keyRequired, ...coverage } = summarizeCoverage(providers);
   const legend = [];
   for (const provider of active)
     for (const entry of provider.legend)
@@ -53,12 +69,7 @@ export function composeUIState({
     keyRequired,
     filter: { ...filter },
     providers: providers.map((p) => ({ ...p, legend: [...p.legend] })),
-    coverage: {
-      loading: active.some((p) => p.loading),
-      count: active.reduce((sum, p) => sum + (p.count || 0), 0),
-      hint: active.find((p) => p.hint)?.hint || '',
-      error: active.find((p) => p.error)?.error || null,
-    },
+    coverage,
     legend,
     sequence: { ...sequence },
     street: { ...street },