feat: route desktop matrix: deep links into the client

Adds useDeepLinkNavigate (mounted in ClientNonUIFeatures): listens for the
'lotus-deeplink' DOM CustomEvent that the Tauri shell dispatches when a
matrix:/matrix.to link opens the app, converts matrix: URIs to matrix.to, and
navigates via the same path as useMentionClickHandler (reusing matrix-to.ts
parsers + useRoomNavigate). No-op outside Tauri.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/hooks/useDeepLinkNavigate.ts

@@ -0,0 +1,98 @@
+import { useCallback, useEffect } from 'react';
+import { useNavigate } from 'react-router-dom';
+import { useMatrixClient } from './useMatrixClient';
+import { useRoomNavigate } from './useRoomNavigate';
+import { isRoomId } from '../utils/matrix';
+import { getHomeRoomPath, withSearchParam } from '../pages/pathUtils';
+import { _RoomSearchParams } from '../pages/paths';
+import { parseMatrixToRoom, parseMatrixToRoomEvent, testMatrixTo } from '../plugins/matrix-to';
+
+/** Desktop (Tauri) injects deep links via a DOM CustomEvent — see lib.rs. */
+const DEEP_LINK_EVENT = 'lotus-deeplink';
+
+const inTauri = (): boolean => '__TAURI_INTERNALS__' in window;
+
+const tryDecode = (value: string): string => {
+  try {
+    return decodeURIComponent(value);
+  } catch {
+    return value;
+  }
+};
+
+/**
+ * Convert a `matrix:` URI (MSC2312) to its `matrix.to` equivalent so we can
+ * reuse the existing matrix.to parsers. Returns undefined for forms we don't
+ * route (e.g. user links, which need an anchor/room context to open a profile).
+ *
+ *   matrix:r/room:server          -> https://matrix.to/#/#room:server
+ *   matrix:roomid/id:server/e/$ev -> https://matrix.to/#/!id:server/$ev
+ */
+const matrixUriToMatrixTo = (uri: string): string | undefined => {
+  const body = uri.slice('matrix:'.length);
+  const [pathPart, queryPart] = body.split('?');
+  const segments = pathPart.split('/');
+  if (segments.length < 2) return undefined;
+
+  const [kind, rawId, evKind, rawEventId] = segments;
+  const sigil = kind === 'r' ? '#' : kind === 'roomid' ? '!' : undefined;
+  if (!sigil || !rawId) return undefined;
+
+  let fragment = `${sigil}${tryDecode(rawId)}`;
+  if (evKind === 'e' && rawEventId) {
+    fragment += `/$${tryDecode(rawEventId)}`;
+  }
+  const query = queryPart ? `?${queryPart}` : '';
+  return `https://matrix.to/#/${fragment}${query}`;
+};
+
+/**
+ * Routes deep links opened from outside the app (Windows `matrix:` links,
+ * forwarded from Tauri) into the client, mirroring the navigation in
+ * useMentionClickHandler. No-op outside Tauri.
+ */
+export const useDeepLinkNavigate = (): void => {
+  const mx = useMatrixClient();
+  const navigate = useNavigate();
+  const { navigateRoom, navigateSpace } = useRoomNavigate();
+
+  const navigateUri = useCallback(
+    (rawUrl: string) => {
+      const href = rawUrl.startsWith('matrix:') ? matrixUriToMatrixTo(rawUrl) : rawUrl;
+      if (!href || !testMatrixTo(href)) return;
+
+      const roomEvent = parseMatrixToRoomEvent(href);
+      const target = roomEvent ?? parseMatrixToRoom(href);
+      if (!target) return; // users / unsupported forms
+
+      const { roomIdOrAlias, viaServers } = target;
+      const eventId = roomEvent?.eventId;
+
+      // Already-joined room/space: navigate directly.
+      if (isRoomId(roomIdOrAlias) && mx.getRoom(roomIdOrAlias)) {
+        if (mx.getRoom(roomIdOrAlias)?.isSpaceRoom()) navigateSpace(roomIdOrAlias);
+        else navigateRoom(roomIdOrAlias, eventId);
+        return;
+      }
+
+      // Otherwise route through the home path (triggers the join/preview flow).
+      const path = getHomeRoomPath(roomIdOrAlias, eventId);
+      navigate(
+        viaServers && viaServers.length > 0
+          ? withSearchParam<_RoomSearchParams>(path, { viaServers: viaServers.join(',') })
+          : path,
+      );
+    },
+    [mx, navigate, navigateRoom, navigateSpace],
+  );
+
+  useEffect(() => {
+    if (!inTauri()) return undefined;
+    const handler = (evt: Event) => {
+      const { detail } = evt as CustomEvent<unknown>;
+      if (typeof detail === 'string') navigateUri(detail);
+    };
+    window.addEventListener(DEEP_LINK_EVENT, handler);
+    return () => window.removeEventListener(DEEP_LINK_EVENT, handler);
+  }, [navigateUri]);
+};

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -34,6 +34,7 @@ import { useSelectedRoom } from '../../hooks/router/useSelectedRoom';
 import { useInboxNotificationsSelected } from '../../hooks/router/useInbox';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { usePresenceUpdater } from '../../hooks/usePresenceUpdater';
+import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
 import { toastQueueAtom } from '../../state/toast';
 
 function isInQuietHours(start: string, end: string): boolean {
@@ -376,6 +377,11 @@ type ClientNonUIFeaturesProps = {
   children: ReactNode;
 };
 
+function DeepLinkNavigator() {
+  useDeepLinkNavigate();
+  return null;
+}
+
 export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
   return (
     <>
@@ -385,6 +391,7 @@ export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
       <PresenceUpdater />
       <InviteNotifications />
       <MessageNotifications />
+      <DeepLinkNavigator />
       {children}
     </>
   );