fix(plex,channels): deep-review fixes — durable watch-sync + no shared-link clobber

Deep-review of the quickfix batch surfaced two data/preference-loss bugs plus
smaller items; all fixed with tests.

- watch_sync _pull_apply: don't let the Plex-authoritative pull overwrite a DIRTY
  local row (a change whose immediate push failed) — that stranded the value
  forever since _repush_dirty only retries dirty rows. Leave it dirty for re-push.
- PlexProvider / ChannelsProvider: a partial shared link opened in a fresh tab
  persisted mount-time DEFAULTS over the account's stored scope/sort/filters
  (base read before the account was pinned). Persist/keep only URL-present dims;
  re-hydrate the omitted ones from storage.
- playback resume write-back: guard against out-of-order delivery (a superseded
  older push now drops) and evict the throttle map so it can't grow unbounded.
- PlexPlayer: announce mid-playback buffering to assistive tech (role=status +
  sr-only label); new plex.player.buffering (HU+EN).
- columnSort: hoist the shared key:dir sort codec used by both URL-state modules.
- Tests: dirty-guard + flag-settle + per-key throttle scoping + superseded-push
  (backend); hold-repeat/suppress-click/unmount + partial-link no-clobber +
  refetch-doesn't-clobber-undo (frontend). Backend pytest 475, FE vitest 519.

frontend/src/components/PersonalViewsModal.dom.test.tsx

@@ -80,11 +80,12 @@ function mount() {
   const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
   qc.setQueryData(qk.tags(), [{ id: 1, name: "Docu" }]);
   vi.spyOn(api, "tags").mockResolvedValue([{ id: 1, name: "Docu" }] as never);
-  return render(
+  const utils = render(
     <QueryClientProvider client={qc}>
       <PersonalViewsModal />
     </QueryClientProvider>,
   );
+  return { ...utils, qc };
 }
 
 beforeEach(() => {
@@ -92,6 +93,8 @@ beforeEach(() => {
   h.saveCurrent.mockClear();
   h.rename.mockClear();
   h.activeViewId = null;
+  // Fresh baseline each test — one test mutates CTX.views to simulate a refetch.
+  CTX.views = [{ id: 5, name: "Docs", filters: VIEW_FILTERS, position: 0, is_default: false }];
 });
 afterEach(() => {
   cleanup();
@@ -119,6 +122,39 @@ describe("PersonalViewsModal — S7 editable detail pane", () => {
     expect(h.updateFilters.mock.calls[1]![1]).toMatchObject({ tags: [1] });
   });
 
+  it("a same-view refetch (new-identity filters) does not wipe the undo history", async () => {
+    // Guards the [selectedId]-only re-seed effect (its exhaustive-deps disable): after a chip prune the
+    // real provider refetches and hands back the SAME view id with a fresh-identity filters object. The
+    // draft must NOT re-seed on that (it would destroy the undo history and the Undo control). A deps
+    // regression that added selected.filters would make this fail.
+    const { rerender, qc } = mount();
+    fireEvent.click(await screen.findByLabelText("feed.chips.remove"));
+    await waitFor(() => expect(h.updateFilters).toHaveBeenCalledTimes(1));
+    expect(await screen.findByLabelText("common.undo")).toBeTruthy();
+
+    // Simulate the post-write refetch: same id 5, new object identity, carrying the pruned value.
+    CTX.views = [
+      {
+        id: 5,
+        name: "Docs",
+        filters: { ...VIEW_FILTERS, tags: [] },
+        position: 0,
+        is_default: false,
+      },
+    ];
+    rerender(
+      <QueryClientProvider client={qc}>
+        <PersonalViewsModal />
+      </QueryClientProvider>,
+    );
+
+    // Undo history survived the refetch — the control is still there and still re-persists on click.
+    const undo = await screen.findByLabelText("common.undo");
+    fireEvent.click(undo);
+    await waitFor(() => expect(h.updateFilters).toHaveBeenCalledTimes(2));
+    expect(h.updateFilters.mock.calls[1]![1]).toMatchObject({ tags: [1] });
+  });
+
   it("Save-current stores the live filters into the view when it isn't already the active one", async () => {
     mount();
     fireEvent.click(await screen.findByText("views.saveCurrent"));