fix: channel deletion navigates to space root instead of @me

Add stale-channel guard in AppLayout that redirects to the space root
when the URL's channelId no longer exists in the channel list. Remove
the hardcoded navigate('/channels/@me') from ChannelSettingsModal and
the redundant setCurrentChannel fallback from the WS channel_deleted
handler — AppLayout's guard now handles all cases uniformly.

packages/web/src/components/layout/AppLayout.tsx

@@ -240,6 +240,20 @@ export function AppLayout() {
     }
   }, [spaceId, channelId, channels, navigate]);
 
+  // Guard: redirect when URL channelId no longer exists (deleted, permission revoked, etc.)
+  useEffect(() => {
+    if (!spaceId || spaceId === '@me' || !channelId) return;
+    if (channels.length === 0) return;
+
+    const { channelToSpaceMap } = useSpaceStore.getState();
+    const firstCh = channels[0];
+    if (!firstCh || channelToSpaceMap.get(firstCh.id) !== spaceId) return;
+
+    if (!channels.some(c => c.id === channelId)) {
+      navigate(`/channels/${spaceId}`, { replace: true });
+    }
+  }, [spaceId, channelId, channels, navigate]);
+
   if (isLoading || !user) {
     return (
       <div className="h-screen flex items-center justify-center bg-surface-chat">

packages/web/src/components/modals/ChannelSettingsModal.tsx

@@ -1,10 +1,8 @@
 import React, { useState, useEffect } from 'react';
-import { useNavigate } from 'react-router-dom';
 import { Modal } from '../ui/Modal';
 import { ConfirmDialog } from '../ui/ConfirmDialog';
 import { useUIStore } from '../../stores/uiStore';
 import { useSpaceStore, getApiForOrigin } from '../../stores/spaceStore';
-import { useChatStore } from '../../stores/chatStore';
 import { api } from '../../api/client';
 import { PermissionBits, permissionsToString, stringToPermissions, hasPermissionBit } from '../../utils/permissions';
 
@@ -24,8 +22,6 @@ export function ChannelSettingsModal() {
   const channels = useSpaceStore((s) => s.channels);
   const spaces = useSpaceStore((s) => s.spaces);
   const spacePermissions = useSpaceStore((s) => s.spacePermissions);
-  const currentChannelId = useChatStore((s) => s.currentChannelId);
-  const navigate = useNavigate();
 
   const [isPrivate, setIsPrivate] = useState(false);
   const [isLoading, setIsLoading] = useState(false);
@@ -116,9 +112,6 @@ export function ChannelSettingsModal() {
       const channelApi = getApiForOrigin(space?._instanceOrigin ?? '');
       await channelApi.channels.delete(channelId);
       closeModal();
-      if (currentChannelId === channelId) {
-        navigate('/channels/@me');
-      }
     } catch (err) {
       setError(err instanceof Error ? err.message : 'Failed to delete channel');
       setIsDeleting(false);