fix: codex S2 review — race conditions, try/finally, scroll, compose reset

- channel switch clears messages immediately, prevents stale fetch overwrite
- auto-scroll only on NEW messages (not every poll cycle)
- ComposeBox keyed by channelId — resets draft on switch
- try/finally on all mutations — failed sends don't disable compose
- loadChannels no longer re-fetches on every channel select

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/colony/src/App.tsx

@@ -12,35 +12,52 @@ export default function App() {
   const [messages, setMessages] = useState<Message[]>([]);
   const [replyTo, setReplyTo] = useState<string | null>(null);
   const scrollRef = useRef<HTMLDivElement>(null);
+  const prevMsgCountRef = useRef(0);
+  const activeChannelRef = useRef(activeChannelId);
+
+  // Keep ref in sync
+  activeChannelRef.current = activeChannelId;
 
   const loadChannels = useCallback(async () => {
     const chs = await getChannels();
     setChannels(chs);
-    if (!activeChannelId && chs.length > 0) {
-      setActiveChannelId(chs[0].id);
-    }
-  }, [activeChannelId]);
+    // Auto-select first channel only if none selected
+    setActiveChannelId((prev) => (prev ? prev : chs[0]?.id ?? null));
+  }, []);
 
   const loadMessages = useCallback(async () => {
-    if (!activeChannelId) return;
-    const msgs = await getMessages(activeChannelId);
-    setMessages(msgs);
-  }, [activeChannelId]);
+    const channelId = activeChannelRef.current;
+    if (!channelId) return;
+    try {
+      const msgs = await getMessages(channelId);
+      // Only update if we're still on the same channel (prevent race)
+      if (activeChannelRef.current === channelId) {
+        setMessages(msgs);
+      }
+    } catch {
+      // Silently ignore fetch errors during polling
+    }
+  }, []);
 
+  // Initial channel load
   useEffect(() => {
     loadChannels();
   }, [loadChannels]);
 
+  // Load messages on channel switch
   useEffect(() => {
-    loadMessages();
+    setMessages([]); // Clear immediately on switch
     setReplyTo(null);
-  }, [loadMessages]);
+    prevMsgCountRef.current = 0;
+    loadMessages();
+  }, [activeChannelId, loadMessages]);
 
-  // Auto-scroll on new messages
+  // Auto-scroll only when NEW messages arrive (not on every poll)
   useEffect(() => {
-    if (scrollRef.current) {
+    if (messages.length > prevMsgCountRef.current && scrollRef.current) {
       scrollRef.current.scrollTop = scrollRef.current.scrollHeight;
     }
+    prevMsgCountRef.current = messages.length;
   }, [messages]);
 
   // Poll until WebSocket (S5)
@@ -51,13 +68,14 @@ export default function App() {
 
   const messagesById = new Map(messages.map((m) => [m.id, m]));
   const activeChannel = channels.find((c) => c.id === activeChannelId);
+  const _currentUser = getCurrentUsername();
 
   return (
     <div className="flex h-full">
       <ChannelSidebar
         channels={channels}
         activeId={activeChannelId}
-        onSelect={(id) => setActiveChannelId(id)}
+        onSelect={setActiveChannelId}
         onChannelCreated={loadChannels}
       />
 
@@ -105,9 +123,10 @@ export default function App() {
           ))}
         </div>
 
-        {/* Compose */}
+        {/* Compose — key forces reset on channel switch */}
         {activeChannelId && (
           <ComposeBox
+            key={activeChannelId}
             channelId={activeChannelId}
             replyTo={replyTo}
             onClearReply={() => setReplyTo(null)}