feat(desktop): Tier B web side — toast actions, Focus Assist gate, folder DnD

- P5-41/35 useTauriToastActions: native rich-toast click → navigate(path) (opens
  the room), quick reply → mx.sendMessage(roomId, m.text). The desktop bridge
  routes message notifications (tag=roomId) to show_rich_toast.
- P5-56 useTauriFocusAssist + focusAssistActiveAtom: a native focus-assist-changed
  event drives the atom, OR'd into the existing quiet-hours gate in
  ClientNonUIFeatures so notifications+sounds suppress during Windows Focus Assist.
- P5-48 recursive folder drag-drop: fileEntries.ts (sync webkitGetAsEntry capture
  → async batched readEntries traversal, path-prefixed names, 500-file cap) wired
  into useFileDrop, reusing the existing upload pipeline. +3 unit tests.

Hooks no-op in the browser. Gates: tsc/eslint/prettier clean, build OK, 559 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/hooks/useFileDrop.ts

@@ -1,11 +1,14 @@
 import { useCallback, DragEventHandler, RefObject, useState, useEffect, useRef } from 'react';
-import { getDataTransferFiles } from '../utils/dom';
+import { collectDroppedFiles } from '../utils/fileEntries';
 
 export const useFileDropHandler = (onDrop: (file: File[]) => void): DragEventHandler =>
   useCallback(
     (evt) => {
-      const files = getDataTransferFiles(evt.dataTransfer);
-      if (files) onDrop(files);
+      // `collectDroppedFiles` synchronously captures the entry list from the
+      // DataTransfer before traversing folders asynchronously.
+      collectDroppedFiles(evt.dataTransfer).then((files) => {
+        if (files) onDrop(files);
+      });
     },
     [onDrop],
   );
@@ -24,8 +27,12 @@ export const useFileDropZone = (
       dragCounterRef.current = 0;
       setActive(false);
       if (!evt.dataTransfer) return;
-      const files = getDataTransferFiles(evt.dataTransfer);
-      if (files) onDrop(files);
+      // Capture entries synchronously (inside the event) then traverse any
+      // dropped folders asynchronously — the DataTransferItemList is emptied
+      // once this handler returns.
+      collectDroppedFiles(evt.dataTransfer).then((files) => {
+        if (files) onDrop(files);
+      });
     };
 
     target?.addEventListener('drop', handleDrop);

src/app/hooks/useTauriFocusAssist.ts

@@ -0,0 +1,24 @@
+import { useSetAtom } from 'jotai';
+import { focusAssistActiveAtom } from '../state/focusAssist';
+import { useTauriEvent } from './useTauri';
+
+/** Detail shape of the `focus-assist-changed` event emitted by the native side. */
+type FocusAssistChangedDetail = {
+  active: boolean;
+};
+
+/**
+ * P5-56 — Windows Focus Assist ↔ Do-Not-Disturb sync (desktop). Subscribes to
+ * the native `focus-assist-changed` event (Windows `SHQueryUserNotificationState`
+ * poll, `{ active }`) and mirrors it into `focusAssistActiveAtom`, which the
+ * notification gate reads to suppress notifications while the shell is in Focus
+ * Assist / Quiet Hours, presenting, gaming full-screen, or busy. Inert in the
+ * browser, since `useTauriEvent` only listens under Tauri.
+ */
+export function useTauriFocusAssist(): void {
+  const setFocusAssist = useSetAtom(focusAssistActiveAtom);
+
+  useTauriEvent<FocusAssistChangedDetail>('focus-assist-changed', ({ active }) =>
+    setFocusAssist(active),
+  );
+}

src/app/hooks/useTauriToastActions.ts

@@ -0,0 +1,39 @@
+import { useNavigate } from 'react-router-dom';
+import { MsgType } from 'matrix-js-sdk';
+import { useMatrixClient } from './useMatrixClient';
+import { useTauriEvent } from './useTauri';
+
+/** Payload of the `lotus-notification-activate` event (a plain body click). */
+interface ActivateDetail {
+  path?: string;
+}
+
+/** Payload of the `lotus-notification-reply` event (the inline reply box). */
+interface ReplyDetail {
+  roomId?: string;
+  text?: string;
+}
+
+/**
+ * P5-41 / P5-35 — wire the native WinRT toast's click + quick-reply back into the
+ * client. The Rust side (`show_rich_toast`) dispatches DOM CustomEvents via
+ * `emit_to_web`:
+ *  - `lotus-notification-activate` → route to the room the toast was for, reusing
+ *    the same `useNavigate(path)` mechanism the web `notificationclick` path uses
+ *    (see ClientNonUIFeatures).
+ *  - `lotus-notification-reply` → send the typed reply straight to the room.
+ * No-op outside Tauri (the events never fire).
+ */
+export function useTauriToastActions(): void {
+  const navigate = useNavigate();
+  const mx = useMatrixClient();
+
+  useTauriEvent<ActivateDetail>('lotus-notification-activate', ({ path }) => {
+    if (path) navigate(path);
+  });
+
+  useTauriEvent<ReplyDetail>('lotus-notification-reply', ({ roomId, text }) => {
+    if (!roomId || !text) return;
+    mx.sendMessage(roomId, { msgtype: MsgType.Text, body: text }).catch(() => undefined);
+  });
+}