feat(ms22-p2): add agent selector UI in WebUI (#685)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/web/src/hooks/useChat.ts

@@ -27,6 +27,7 @@ export interface UseChatOptions {
   maxTokens?: number;
   systemPrompt?: string;
   projectId?: string | null;
+  agent?: string;
   onError?: (error: Error) => void;
 }
 
@@ -63,6 +64,7 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
     maxTokens,
     systemPrompt,
     projectId,
+    agent,
     onError,
   } = options;
 
@@ -77,6 +79,10 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
   const projectIdRef = useRef<string | null>(projectId ?? null);
   projectIdRef.current = projectId ?? null;
 
+  // Track agent in ref to prevent stale closures
+  const agentRef = useRef<string | undefined>(agent);
+  agentRef.current = agent;
+
   // Track messages in ref to prevent stale closures during rapid sends
   const messagesRef = useRef<Message[]>(messages);
   messagesRef.current = messages;
@@ -209,6 +215,7 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
         ...(temperature !== undefined && { temperature }),
         ...(maxTokens !== undefined && { maxTokens }),
         ...(systemPrompt !== undefined && { systemPrompt }),
+        ...(agentRef.current && { agent: agentRef.current }),
       };
 
       const controller = new AbortController();