fix(sidebar): favourite / low-priority changes move the room immediately

Home's categorisation memo keyed only on the room list, and nothing
observed m.tag changes. The SDK emits RoomEvent.Tags on the room and
re-emits it on the client (room.js addTags, sync.js reEmit); a small
client-level hook bumps a version that the memo depends on.

Fixes #20

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useRoomTagsVersion.ts

@@ -0,0 +1,31 @@
+import { useEffect } from 'react';
+import { MatrixClient, RoomEvent } from 'matrix-js-sdk';
+import { useForceUpdate } from './useForceUpdate';
+
+/**
+ * Bumps a counter whenever any room's `m.tag` account data changes
+ * (favourite/low-priority add or remove via `mx.setRoomTag`/`deleteRoomTag`).
+ *
+ * `RoomEvent.Tags` is emitted on the individual `Room` by `Room.addTags()`
+ * (matrix-js-sdk `lib/models/room.js`) and re-emitted onto the `MatrixClient`
+ * itself by the sync loop (`lib/sync.js`, the `client.reEmitter.reEmit(room, [...
+ * RoomEvent.Tags ...])` call), so a single client-level listener here sees the
+ * change for every room without needing to attach/detach a per-room listener.
+ *
+ * Consumers should add the returned counter to the deps of any memo that
+ * derives favourite/low-priority categorisation from `room.tags`, so toggling
+ * a tag moves the room immediately instead of waiting for an unrelated
+ * re-render to pick up the mutated (but stale-looking) `Room` object.
+ */
+export const useRoomTagsVersion = (mx: MatrixClient): number => {
+  const [version, bumpVersion] = useForceUpdate();
+
+  useEffect(() => {
+    mx.on(RoomEvent.Tags, bumpVersion);
+    return () => {
+      mx.removeListener(RoomEvent.Tags, bumpVersion);
+    };
+  }, [mx, bumpVersion]);
+
+  return version;
+};

src/app/pages/client/home/Home.tsx

@@ -79,6 +79,7 @@ import { UseStateProvider } from '../../../components/UseStateProvider';
 import { JoinAddressPrompt } from '../../../components/join-address-prompt';
 import { _RoomSearchParams } from '../../paths';
 import { getLocalRoomNamesContent } from '../../../hooks/useRoomMeta';
+import { useRoomTagsVersion } from '../../../hooks/useRoomTagsVersion';
 
 type HomeMenuProps = {
   requestClose: () => void;
@@ -253,6 +254,11 @@ export function Home() {
   const [homeRoomSort, setHomeRoomSort] = useSetting(settingsAtom, 'homeRoomSort');
   const roomToUnread = useAtomValue(roomToUnreadAtom);
   const [sortMenuAnchor, setSortMenuAnchor] = useState<RectCords>();
+  // Bumped whenever any room's `m.tag` account data changes (favourite/low-priority
+  // toggle via RoomNavItemMenu). Nothing else re-runs this memo on a tag change
+  // (see useRoomTagsVersion.ts), so without this dep a room only moves section
+  // once some unrelated event (e.g. an unread-count change) forces a re-render.
+  const roomTagsVersion = useRoomTagsVersion(mx);
 
   const { favoriteRooms, lowPriorityRooms, otherRooms } = useMemo(() => {
     const favs: string[] = [];
@@ -269,7 +275,10 @@ export function Home() {
       }
     });
     return { favoriteRooms: favs, lowPriorityRooms: low, otherRooms: others };
-  }, [mx, rooms]);
+    // roomTagsVersion is a trigger-only counter, not read in the body; it forces
+    // this memo to re-run whenever any room's tags change.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [mx, rooms, roomTagsVersion]);
 
   const sortedFavoriteRooms = useMemo(() => {
     const isClosed = closedCategories.has(FAVORITES_CATEGORY_ID);