feat(web): add WebSocket chat handler with message persistence

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/server/ws/chat.ts

@@ -0,0 +1,61 @@
+import { WebSocket } from 'ws';
+import { randomUUID } from 'crypto';
+import { getDb } from '../db';
+
+export function handleChat(ws: WebSocket) {
+  let conversationId: string | null = null;
+
+  ws.on('message', async (raw) => {
+    try {
+      const msg = JSON.parse(raw.toString());
+
+      if (msg.type === 'init') {
+        conversationId = msg.conversationId || randomUUID();
+        const history = getDb().prepare(
+          'SELECT * FROM messages WHERE conversation_id = ? ORDER BY created_at'
+        ).all(conversationId);
+        ws.send(JSON.stringify({ type: 'history', data: { conversationId, messages: history } }));
+        return;
+      }
+
+      if (msg.type === 'chat') {
+        const { content } = msg;
+        const msgId = randomUUID();
+
+        getDb().prepare(
+          'INSERT INTO messages (id, conversation_id, role, content) VALUES (?, ?, ?, ?)'
+        ).run(msgId, conversationId, 'user', content);
+
+        ws.send(JSON.stringify({ type: 'message', data: { id: msgId, role: 'user', content } }));
+
+        // Assistant echo (placeholder until LLM integration in Task 3.3)
+        const assistantId = randomUUID();
+        const assistantContent = `收到你的消息：「${content}」。Agent 引擎正在启动中...`;
+
+        getDb().prepare(
+          'INSERT INTO messages (id, conversation_id, role, content) VALUES (?, ?, ?, ?)'
+        ).run(assistantId, conversationId, 'assistant', assistantContent);
+
+        ws.send(JSON.stringify({
+          type: 'message',
+          data: { id: assistantId, role: 'assistant', content: assistantContent },
+        }));
+      }
+
+      if (msg.type === 'create_conversation') {
+        const { title, accountId } = msg;
+        conversationId = randomUUID();
+        getDb().prepare(
+          'INSERT INTO conversations (id, title, account_id) VALUES (?, ?, ?)'
+        ).run(conversationId, title || '新对话', accountId || null);
+        ws.send(JSON.stringify({ type: 'conversation_created', data: { id: conversationId, title } }));
+      }
+    } catch (e) {
+      ws.send(JSON.stringify({ type: 'error', data: { message: (e as Error).message } }));
+    }
+  });
+
+  ws.on('close', () => {
+    // cleanup if needed
+  });
+}