fix(security): bookmarks/reminders stop storing decrypted text server-side

For encrypted rooms, bookmarks persist only {roomId, eventId, savedAt}
and reminders only their non-text fields; the preview, room name and
sender resolve locally at render/fire time from the timeline (with a
"Message unavailable" fallback). A one-time, loop-guarded cleanup strips
text from existing entries in currently-encrypted rooms. Unencrypted
rooms are unchanged. Unit-tested.

Fixes #10

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

src/app/features/bookmarks/BookmarksPanel.tsx

@@ -103,7 +103,8 @@ function BookmarkItem({ bookmark, onJump, onRemove, preview, senderName }: Bookm
   const mx = useMatrixClient();
   const useAuthentication = useMediaAuthentication();
   const room = mx.getRoom(bookmark.roomId) ?? undefined;
-  const displayRoomName = room?.name ?? bookmark.roomName;
+  // E2EE-room bookmarks store no roomName; fall back past the '' placeholder.
+  const displayRoomName = room?.name || bookmark.roomName || 'Unknown room';
   const avatarUrl = room
     ? (getRoomAvatarUrl(mx, room, 96, useAuthentication) ?? undefined)
     : undefined;
@@ -162,7 +163,7 @@ function BookmarkItem({ bookmark, onJump, onRemove, preview, senderName }: Bookm
         style={{ justifyContent: 'flex-start', height: 'unset', padding: config.space.S200 }}
       >
         <Text className={css.BookmarkPreview} size="T200" priority="400">
-          {preview ?? (bookmark.previewText || '(no preview)')}
+          {preview ?? (bookmark.previewText || 'Message unavailable')}
         </Text>
       </Button>
     </Box>
@@ -173,13 +174,16 @@ type LiveBookmarkItemProps = BookmarkItemProps & { room: Room };
 
 // Renders the same layout as BookmarkItem, but resolves the message body live so
 // edits (m.replace, applied by useRoomEvent) and redactions are reflected. The
-// stored snapshot (previewText) remains the fallback for loading/failed/empty states.
+// stored snapshot (previewText) remains the fallback for loading/failed/empty
+// states; bookmarks from E2EE rooms have no snapshot at all (account data is
+// server-readable), so the live event is their only source of text.
 function LiveBookmarkItem({ room, bookmark, onJump, onRemove }: LiveBookmarkItemProps) {
   const liveEvent = useRoomEvent(room, bookmark.eventId, () =>
     room.findEventById(bookmark.eventId),
   );
 
-  const snapshot = bookmark.previewText || '(no preview)';
+  const snapshot =
+    bookmark.previewText || (liveEvent === undefined ? 'Loading…' : 'Message unavailable');
   let preview: ReactNode = snapshot;
 
   // undefined (loading) and null (fetch failed / not found) both keep the snapshot.
@@ -234,7 +238,7 @@ function RoomGroupHeader({
   const mx = useMatrixClient();
   const useAuthentication = useMediaAuthentication();
   const room = mx.getRoom(roomId) ?? undefined;
-  const displayRoomName = room?.name ?? roomName;
+  const displayRoomName = room?.name || roomName || 'Unknown room';
   const avatarUrl = room
     ? (getRoomAvatarUrl(mx, room, 96, useAuthentication) ?? undefined)
     : undefined;
@@ -327,13 +331,20 @@ export function BookmarksPanel({ onClose }: BookmarksPanelProps) {
     () =>
       query.length === 0
         ? bookmarks
-        : bookmarks.filter(
-            (bk) =>
-              bk.previewText.toLowerCase().includes(query) ||
+        : bookmarks.filter((bk) => {
+            // E2EE-room bookmarks have no stored text: match against the locally
+            // cached event body / live room name instead (nothing is fetched here).
+            const room = mx.getRoom(bk.roomId);
+            const localBody = room?.findEventById(bk.eventId)?.getContent()?.body;
+            return (
+              (bk.previewText?.toLowerCase().includes(query) ?? false) ||
+              (typeof localBody === 'string' && localBody.toLowerCase().includes(query)) ||
               bk.roomName.toLowerCase().includes(query) ||
-              (bk.senderName?.toLowerCase().includes(query) ?? false),
-          ),
-    [bookmarks, query],
+              (room?.name.toLowerCase().includes(query) ?? false) ||
+              (bk.senderName?.toLowerCase().includes(query) ?? false)
+            );
+          }),
+    [mx, bookmarks, query],
   );
 
   // Prune collapsed roomIds that no longer have any bookmark, so a room re-saved

src/app/features/room/message/Message.tsx

@@ -1273,6 +1273,9 @@ export const Message = React.memo(
                                     const content = mEvent.getContent();
                                     const body: string =
                                       (content?.body as string | undefined) ?? '';
+                                    // For E2EE rooms useBookmarks strips the text
+                                    // fields before persisting (account data is
+                                    // server-readable); the panel resolves them live.
                                     addBookmark({
                                       roomId: room.roomId,
                                       eventId,