Add UxGallery.libraryChanges — a Stream<void> that emits whenever the
underlying photo library reports a change, so picker UIs can drop
their cached asset lists and reload reactively.
- iOS: GalleryPlugin conforms to PHPhotoLibraryChangeObserver +
FlutterStreamHandler; on photoLibraryDidChange the fetchCache is
cleared and a void event is pushed over ux/gallery/changes. The
observer is registered lazily on the first granted/limited
authorization so plugin init doesn't trigger iOS's permission
evaluation at app launch.
- macOS: near-verbatim port of the iOS shape (same Photos.framework,
same fetchCache staleness, same fix).
- Android: registers a MediaStore ContentObserver on
Files.getContentUri(VOLUME_EXTERNAL) with notifyForDescendants =
true; observer lifecycle tracks the Dart subscription (registered
on onListen, unregistered on onCancel / plugin detach). No native
cache to invalidate today, but the pipeline is wired for the
upcoming READ_MEDIA_VISUAL_USER_SELECTED limited-access work.
- iOS presentLimitedLibraryPicker switched to the iOS 15+ completion-
handler variant so the Dart await resolves on dismissal, not on
presentation. The actual reload is now driven by the change
observer (which fires after iOS commits the new subset),
side-stepping the completion-vs-commit race that produced an
off-by-one in the picker on consecutive MANAGE taps.
- FakeUxGalleryBackend exposes emitLibraryChange() so tests can
drive the reactive-reload wiring without going through the real
method channel.
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