LIVE 模式改為雙向對話,參考 claudecodeui 的 resume 接力機制

摘要：
側邊面板從單向任務派發升級為聊天室:每則訊息 spawn
claude -p --output-format stream-json,捕捉 session_id 後
下一則自動 --resume 接力,對話得以連續;回覆同步顯示在
聊天串與小人頭上的對話氣泡。

根本原因：
單向 /task 發出後看不到回覆內容,也無法追問;claudecodeui
證明 headless + resume 接力即可實現連續對話,無需常駐 runtime。

影響：
watcher 新增 POST /chat(每專案一個 office thread、busy 檢查、
reset 會終止進行中的執行);SSE 新增 chat_start/chat_text/chat_done。
/task API 保留。已實測兩輪對話,第二輪正確記得第一輪內容。

修法：
- watch.mjs:launchChat 解析 stream-json(init 抓 session_id、
  assistant 文字轉發、result 收尾),chatThreads 記憶 thread
- store:chats Map + chatAppend/chatSetBusy/chatClear
- live.ts:sendChat/resetChat + chat_* 事件對映
- SidePanel:ChatPanel(氣泡串、自動捲底、Enter 送出、新對話)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/watch.mjs

@@ -312,6 +312,154 @@ async function launchTask(slug, prompt, resume) {
   });
 }
 
+/* ── two-way chat: one office thread per project, stitched with --resume ── */
+
+/** slug → { sessionId, child } */
+const chatThreads = new Map();
+
+async function launchChat(slug, message, fromProject) {
+  const proj = projects.get(slug);
+  if (!proj?.cwd) return { ok: false, error: "unknown project" };
+
+  let thread = chatThreads.get(slug);
+  if (!thread) {
+    thread = { sessionId: null, child: null };
+    chatThreads.set(slug, thread);
+  }
+  if (thread.child) return { ok: false, error: "busy" };
+
+  let resumeId = thread.sessionId;
+  if (!resumeId && fromProject) {
+    const sid = await newestSessionId(slug);
+    if (sid && /^[0-9a-fA-F-]+$/.test(sid)) resumeId = sid;
+  }
+
+  const args = [
+    "-p",
+    "--output-format",
+    "stream-json",
+    "--verbose",
+    "--permission-mode",
+    PERMISSION_MODE,
+  ];
+  if (resumeId) args.push("--resume", resumeId);
+
+  // Message goes through stdin — never through shell arguments.
+  const child = spawn("claude", args, {
+    cwd: proj.cwd,
+    shell: true,
+    stdio: ["pipe", "pipe", "pipe"],
+    windowsHide: true,
+  });
+  thread.child = child;
+
+  let stderrTail = "";
+  let stdoutRemainder = "";
+  let sawResult = false;
+
+  child.stderr.on("data", (c) => {
+    stderrTail = (stderrTail + c.toString("utf8")).slice(-400);
+  });
+
+  child.stdout.on("data", (c) => {
+    const chunk = stdoutRemainder + c.toString("utf8");
+    const lines = chunk.split("\n");
+    stdoutRemainder = lines.pop() ?? "";
+    for (const line of lines) {
+      if (!line.trim()) continue;
+      let o;
+      try {
+        o = JSON.parse(line);
+      } catch {
+        continue;
+      }
+      if (o.session_id) thread.sessionId = o.session_id;
+      if (o.type === "system" && o.subtype === "init") {
+        broadcast({ type: "chat_start", slug });
+      } else if (o.type === "assistant") {
+        const text = (o.message?.content ?? [])
+          .filter((b) => b && b.type === "text" && b.text)
+          .map((b) => b.text)
+          .join("\n")
+          .trim();
+        if (text) broadcast({ type: "chat_text", slug, text });
+      } else if (o.type === "result") {
+        sawResult = true;
+        broadcast({
+          type: "chat_done",
+          slug,
+          ok: o.subtype === "success",
+          text: typeof o.result === "string" ? o.result : "",
+        });
+      }
+    }
+  });
+
+  child.stdin.write(message);
+  child.stdin.end();
+
+  const killer = setTimeout(() => child.kill(), TASK_TIMEOUT_MS);
+  child.on("close", (code) => {
+    clearTimeout(killer);
+    thread.child = null;
+    if (!sawResult) {
+      broadcast({
+        type: "chat_done",
+        slug,
+        ok: false,
+        text: "",
+        error: stderrTail.trim().slice(-200) || `exit ${code}`,
+      });
+    }
+  });
+  child.on("error", (err) => {
+    clearTimeout(killer);
+    thread.child = null;
+    broadcast({ type: "chat_done", slug, ok: false, text: "", error: String(err).slice(0, 200) });
+  });
+
+  return { ok: true, resumed: Boolean(resumeId) };
+}
+
+async function handleChatRequest(req, res) {
+  const cors = corsFor(req);
+  if (req.method === "OPTIONS") {
+    res.writeHead(Object.keys(cors).length ? 204 : 403, cors);
+    res.end();
+    return;
+  }
+  if (!Object.keys(cors).length) {
+    res.writeHead(403, { "Content-Type": "application/json" });
+    res.end(JSON.stringify({ ok: false, error: "origin not allowed" }));
+    return;
+  }
+  const reply = (status, payload) => {
+    res.writeHead(status, { ...cors, "Content-Type": "application/json" });
+    res.end(JSON.stringify(payload));
+  };
+  try {
+    const body = JSON.parse(await readBody(req));
+    const slug = String(body.slug ?? "");
+    if (!projects.has(slug)) return reply(404, { ok: false, error: "unknown project" });
+
+    if (body.reset) {
+      const thread = chatThreads.get(slug);
+      if (thread?.child) thread.child.kill();
+      chatThreads.delete(slug);
+      return reply(200, { ok: true });
+    }
+
+    const message = String(body.message ?? "").trim();
+    if (!message || message.length > 8000) {
+      return reply(400, { ok: false, error: "message must be 1–8000 chars" });
+    }
+    const result = await launchChat(slug, message, Boolean(body.fromProject));
+    reply(result.ok ? 200 : 409, result);
+  } catch {
+    reply(400, { ok: false, error: "bad request" });
+  }
+}
+
 function corsFor(req) {
   const origin = req.headers.origin;
   if (origin && ALLOWED_ORIGINS.has(origin)) {
@@ -403,6 +551,10 @@ const server = createServer((req, res) => {
     handleTaskRequest(req, res);
     return;
   }
+  if (req.url === "/chat") {
+    handleChatRequest(req, res);
+    return;
+  }
   if (req.url === "/events") {
     res.writeHead(200, {
       "Content-Type": "text/event-stream",