fix(room): handle reaction updates in onRoomMessage WS handler

Root cause: publish_reaction_event sends a RoomMessageEvent (not
reaction_added) with reactions field set. The onRoomMessage handler
previously returned prev immediately when a duplicate ID was found,
skipping the reaction update entirely.

Fix:
- Add reactions field to RoomMessagePayload so TypeScript knows it's there
- When a duplicate message ID is found AND payload carries reactions,
  update the existing message's reactions field instead of ignoring
- ReactionItem and ReactionGroup have identical shapes, so assignment works

src/contexts/room-context.tsx

@@ -424,8 +424,20 @@ export function RoomProvider({
           // Use ref to get current activeRoomId to avoid stale closure
           if (payload.room_id === activeRoomIdRef.current) {
             setMessages((prev) => {
-              // Deduplicate by both ID (for normal) and seq (for optimistic replacement)
-              if (prev.some((m) => m.id === payload.id)) {
+              // Check if this is a reaction-update event (same ID, different reactions).
+              // publish_reaction_event sends RoomMessageEvent with reactions field set.
+              const existingIdx = prev.findIndex((m) => m.id === payload.id);
+              if (existingIdx !== -1) {
+                // Message already exists — update reactions if provided.
+                // Reaction events have empty content/sender_type.
+                if (payload.reactions !== undefined) {
+                  const updated = [...prev];
+                  updated[existingIdx] = { ...updated[existingIdx], reactions: payload.reactions };
+                  const msg = updated[existingIdx];
+                  saveMessage(msg).catch(() => {});
+                  return updated;
+                }
+                // Duplicate of a real message — ignore
                 return prev;
               }
               // Also check if there's an optimistic message with the same seq that should be replaced

src/lib/ws-protocol.ts

@@ -166,6 +166,8 @@ export interface RoomMessagePayload {
   send_at: string;
   seq: number;
   display_name?: string;
+  /** Present when this event carries reaction updates for the message */
+  reactions?: ReactionItem[];
 }
 
 export interface ProjectEventPayload {