## Summary
Fixes metadata lifecycle bugs during sign-in, sign-out, and locale
change:
- **Cross-tab sign-out**: Broadcasts sign-out via `BroadcastChannel` so
other tabs clear their session gracefully instead of hitting stale-token
errors
- **SSE teardown on sign-out**: Handles `UNAUTHENTICATED`/`FORBIDDEN`
errors in the SSE event stream effect instead of throwing unhandled
errors
- **Locale switch resilience**: `invalidateAndReload` now invalidates
collection hashes instead of clearing the store to empty, so components
never see 0 metadata items during the reload transition
- **Sign-in background mock**: Uses non-throwing
`objectMetadataItemFamilySelector` instead of hooks that throw on
missing metadata
- **View name placeholders**: Guards against `undefined` `viewName`
during metadata transitions (the minimal metadata query doesn't include
`name`)
- **Session cleanup**: Selective `localStorage` clearing
(`clearSessionLocalStorageKeys`) preserves metadata keys;
`clearAllSessionLocalStorageKeys` for full clears
- **Metadata reload API**: New `useMetadataStoreActions` hook as the
high-level API for metadata lifecycle operations (`applyMockedMetadata`,
`invalidateAndReload`, `loadMockedMetadataAtomic`)
## Test plan
- [ ] Sign out on Tab A → Tab A shows sign-in page with no console
errors
- [ ] Tab B (logged in) receives cross-tab broadcast and redirects to
sign-in
- [ ] No "Forbidden resource" SSE errors in console during sign-out
- [ ] Change language in Settings > Experience → no crash, metadata
refreshes in background
- [ ] Sign back in after sign-out → metadata loads correctly, app is
functional
- [ ] Re-sign-in after locale change → correct locale is preserved
