feat(desktop): update failures say what happened and what to do

A friend's update failed ten times in a row ("Update check failed: error
sending request for url (…nsis.zip)") before the 11th went through, and
he didn't know what to do. The label was also wrong: the check had
worked; the download failed.

- Progress: "Downloading update… 28% (14.3 MB of 49.9 MB)", "The update
  server didn't respond. Trying again in 3 s (attempt 2 of 4)…", from the
  native `lotus-update-progress` events (cinny-desktop retries itself).
- Failures name the step (check / download / install, from the native
  error prefix) in plain language, with Try again and a Download
  installer button (Windows: the setup .exe; else the release page), and
  the raw error under "Details".
- Installing from the update toast now shows a "Downloading update"
  toast, and on failure a sticky "Update didn't install" toast that
  retries on click and points at Settings → General → App Updates.
  Before, the toast vanished and the failure was only visible in Settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -1,6 +1,7 @@
 import { useAtomValue, useSetAtom } from 'jotai';
 import React, { ReactNode, useCallback, useEffect, useRef } from 'react';
 import { useNavigate } from 'react-router-dom';
+import { Icons } from 'folds';
 import {
   ClientEvent,
   ClientEventHandlerMap,
@@ -62,10 +63,11 @@ import {
 import { STATUS_EXPIRY_KEY, STATUS_MSG_KEY } from '../../features/settings/account/Profile';
 import { setPresenceWithRetry } from '../../utils/presenceWrite';
 import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
-import { toastQueueAtom } from '../../state/toast';
+import { dismissToastAtom, toastQueueAtom } from '../../state/toast';
 import { useReminders } from '../../hooks/useReminders';
 import { getRoomRetentionMs, isExpired } from '../../utils/retention';
-import { useTauriUpdater } from '../../hooks/useTauriUpdater';
+import { useTauriUpdateProgress, useTauriUpdater } from '../../hooks/useTauriUpdater';
+import { isNetworkUpdateError } from '../../utils/updateErrors';
 import { invokeTauri, isTauri as isTauriApp } from '../../hooks/useTauri';
 import { TauriDesktopFeatures } from '../../components/TauriDesktopFeatures';
 import { KeyboardShortcutsDialog, useKeyboardShortcutsTrigger } from '../../features/shortcuts';
@@ -887,11 +889,50 @@ function RetentionSweeper() {
 const TAURI_UPDATE_CHECK_INTERVAL = 12 * 60 * 60_000; // 12 hours
 const TAURI_UPDATE_LAST_CHECK_KEY = 'lotus.tauriUpdateLastCheck';
 
+const UPDATE_PROGRESS_TOAST = 'tauri-update-progress';
+const UPDATE_FAILED_TOAST = 'tauri-update-failed';
+
 function TauriUpdateFeature() {
   const { isTauri, status, check, install } = useTauriUpdater();
+  useTauriUpdateProgress();
   const setToast = useSetAtom(toastQueueAtom);
+  const dismissToast = useSetAtom(dismissToastAtom);
   const firedRef = useRef<string | null>(null);
 
+  // Installing from the toast used to fail invisibly: the toast was gone and
+  // the only trace was an error line in Settings. Say what is happening, and
+  // on failure leave a toast that retries and points at the manual installer.
+  const installFromToast = useCallback(async () => {
+    dismissToast(UPDATE_FAILED_TOAST);
+    setToast({
+      id: UPDATE_PROGRESS_TOAST,
+      iconSrc: Icons.Download,
+      displayName: 'Downloading update',
+      body: 'Lotus Chat will restart by itself when it’s done. You can keep chatting.',
+      roomName: 'System',
+      roomId: '',
+      onClick: () => undefined,
+    });
+    const failure = await install();
+    dismissToast(UPDATE_PROGRESS_TOAST);
+    if (!failure) return;
+    // Short on purpose; the full explanation and a Download installer button
+    // are in Settings → General → App Updates.
+    const busy = failure.phase !== 'install' && isNetworkUpdateError(failure.message);
+    setToast({
+      id: UPDATE_FAILED_TOAST,
+      iconSrc: Icons.Warning,
+      displayName: 'Update didn’t install',
+      body: `${busy ? 'The update server seems busy. ' : ''}Click to try again, or get the installer in Settings → General → App Updates.`,
+      roomName: 'System',
+      roomId: '',
+      sticky: true,
+      onClick: () => {
+        installFromToast();
+      },
+    });
+  }, [install, setToast, dismissToast]);
+
   useEffect(() => {
     if (!isTauri) return;
 
@@ -917,10 +958,12 @@ function TauriUpdateFeature() {
       body: `Lotus Chat ${status.version} is ready. Click to install and restart.`,
       roomName: 'System',
       roomId: '',
-      onClick: install,
+      onClick: () => {
+        installFromToast();
+      },
       sticky: true,
     });
-  }, [status, setToast, install]);
+  }, [status, setToast, installFromToast]);
 
   return null;
 }