File previews read once and then froze: visited tabs stay mounted-but-hidden
(LRU in useMountedTabSet), so refetchOnMount never re-fired and the only way
to see fresh content was to close and reopen the tab.
Gate the file query's `enabled` on tab + app visibility so React Query
refetches on the disabled->enabled transition — and only when the cached read
is stale (keeping the existing 5s staleTime), so a quick flip away and back
doesn't re-read. Covers switching between tabs and backgrounding/reopening the
whole app to the same tab.
Adds a wiring test covering the stale-revisit refetch, the fresh-revisit
debounce, the app-foreground refetch, and the read-error path.
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
