diff --git a/server.py b/server.py
index 6b28c0c..7a46a8e 100644
--- a/server.py
+++ b/server.py
@@ -20,6 +20,7 @@
   GET    /api/threads/<id>                -> thread detail (posts)
   POST   /api/threads/<id>/posts          -> append post
                                               body: { content, speaker? }
+  PATCH  /api/threads/<id>                -> rename title { title }
   POST   /api/threads/<id>/close          -> mark closed
   POST   /api/threads/<id>/posts/<pid>/reactions  -> toggle {emoji, actor?}
 
@@ -1715,6 +1716,30 @@ def do_PATCH(self):
             except forge_favorites.FavoriteValidationError as e:
                 self._json({"error": str(e)}, 400)
             return
+        # v0.10: PATCH /api/threads/<id> — rename thread title.
+        # Body: { title: str }. Empty string allowed (clears explicit title).
+        m = re.match(rf"^/api/threads/{THREAD_ROUTE_RE}$", url.path)
+        if m:
+            tid = m.group(1)
+            if store.project_thread(tid) is None:
+                self._json({"error": "unknown thread"}, 404)
+                return
+            opts = self._read_json()
+            if opts is None:
+                return
+            if not isinstance(opts, dict):
+                self._json({"error": "body must be object"}, 400)
+                return
+            if "title" not in opts:
+                self._json({"error": "`title` field required"}, 400)
+                return
+            try:
+                store.set_thread_title(tid, opts["title"])
+            except ValueError as e:
+                self._json({"error": str(e)}, 400)
+                return
+            self._json(_serializable_thread(store.project_thread(tid)))
+            return
         m = re.match(rf"^/api/threads/{THREAD_ROUTE_RE}/posts/{POST_ID_ROUTE_RE}$", url.path)
         if m:
             tid = m.group(1)
diff --git a/tests/test_thread_title.py b/tests/test_thread_title.py
index 21f7ca8..93cc93d 100644
--- a/tests/test_thread_title.py
+++ b/tests/test_thread_title.py
@@ -167,3 +167,83 @@ def test_server_create_thread_legacy_content_only(server):
     # title is auto-derived from first line
     assert th["title"]
     assert th["title"] in "legacy-style opening"
+
+
+# ─── rename (PATCH) ────────────────────────────────────────────────
+
+
+def _patch(url: str, body: dict) -> dict:
+    req = urllib.request.Request(
+        url,
+        data=json.dumps(body).encode("utf-8"),
+        headers={"Content-Type": "application/json", "X-OpenForge-UI": "1"},
+        method="PATCH",
+    )
+    with urllib.request.urlopen(req, timeout=2) as r:
+        return json.loads(r.read().decode("utf-8"))
+
+
+def test_store_set_thread_title_renames(store):
+    store.create_squad({
+        "id": "rn1", "name": "rn1", "members": ["scott"], "chair": "scott",
+    })
+    t = store.create_thread("rn1", "scott", title="old name")
+    store.set_thread_title(t["thread_id"], "new name")
+    proj = store.project_thread(t["thread_id"])
+    assert proj["title"] == "new name"
+    # summarize / list also reflect new title
+    assert store.summarize_thread(t["thread_id"])["title"] == "new name"
+    assert store.list_threads_for_squad("rn1")[0]["title"] == "new name"
+
+
+def test_store_set_thread_title_length_validation(store):
+    store.create_squad({
+        "id": "rn2", "name": "rn2", "members": ["scott"], "chair": "scott",
+    })
+    t = store.create_thread("rn2", "scott", title="ok")
+    with pytest.raises(ValueError):
+        store.set_thread_title(t["thread_id"], "x" * 81)
+
+
+def test_server_patch_thread_title(server):
+    _post(f"{server}/api/squads", {
+        "id": "rnsv", "name": "rnsv", "members": ["scott"], "chair": "scott",
+    })
+    th = _post(f"{server}/api/squads/rnsv/threads", {
+        "title": "before", "created_by": "scott",
+    })
+    tid = th["thread_id"]
+    out = _patch(f"{server}/api/threads/{tid}", {"title": "after"})
+    assert out["title"] == "after"
+    # GET returns the new title
+    assert _get(f"{server}/api/threads/{tid}")["title"] == "after"
+
+
+def test_server_patch_thread_title_unknown_thread(server):
+    req = urllib.request.Request(
+        f"{server}/api/threads/th_does_not_exist",
+        data=json.dumps({"title": "x"}).encode("utf-8"),
+        headers={"Content-Type": "application/json", "X-OpenForge-UI": "1"},
+        method="PATCH",
+    )
+    with pytest.raises(urllib.error.HTTPError) as excinfo:
+        urllib.request.urlopen(req, timeout=2)
+    assert excinfo.value.code == 404
+
+
+def test_server_patch_thread_title_missing_field(server):
+    _post(f"{server}/api/squads", {
+        "id": "rnmf", "name": "rnmf", "members": ["scott"], "chair": "scott",
+    })
+    th = _post(f"{server}/api/squads/rnmf/threads", {
+        "title": "x", "created_by": "scott",
+    })
+    req = urllib.request.Request(
+        f"{server}/api/threads/{th['thread_id']}",
+        data=json.dumps({}).encode("utf-8"),
+        headers={"Content-Type": "application/json", "X-OpenForge-UI": "1"},
+        method="PATCH",
+    )
+    with pytest.raises(urllib.error.HTTPError) as excinfo:
+        urllib.request.urlopen(req, timeout=2)
+    assert excinfo.value.code == 400
diff --git a/web/app.js b/web/app.js
index f91161b..7383c92 100644
--- a/web/app.js
+++ b/web/app.js
@@ -2707,6 +2707,28 @@ attachComposerPreview(els.postComposerInput);
 attachComposerPreview(els.threadComposerInput);
 els.btnSendPost.onclick = submitPost;
 els.btnCloseThread.onclick = closeCurrentThread;
+// v0.10: double-click thread title to rename.
+els.detailTitle.addEventListener('dblclick', async () => {
+  const tid = state.currentThreadId;
+  if (!tid) return;
+  const current = state.currentThread?.title || els.detailTitle.textContent || '';
+  const next = window.prompt('重命名 thread（最多 80 字）：', current);
+  if (next === null) return;
+  const title = next.trim();
+  if (title === current.trim()) return;
+  try {
+    const updated = await apiJson(`/api/threads/${encodeURIComponent(tid)}`, {
+      method: 'PATCH',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ title }),
+    });
+    state.currentThread = updated;
+    els.detailTitle.textContent = updated.title || updated.preview || '(empty)';
+    refreshThreadsForCurrentSquad();
+  } catch (e) {
+    alert('重命名失败：' + (e?.message || e));
+  }
+});
 els.btnRefreshThreads.onclick = refreshThreadsForCurrentSquad;
 els.btnRefreshDetail.onclick = refreshCurrentThread;
 if (els.btnPopoutThread) {
diff --git a/web/index.html b/web/index.html
index af4008e..94de34c 100644
--- a/web/index.html
+++ b/web/index.html
@@ -134,7 +134,7 @@ <h1 id="squad-title">—</h1>
   <main id="thread-pane">
     <header id="thread-header">
       <div class="thread-header-main">
-        <h2 id="detail-title">选择一个 thread</h2>
+        <h2 id="detail-title" title="双击重命名">选择一个 thread</h2>
         <div id="detail-sub" class="meta"></div>
       </div>
       <div id="detail-participants" class="avatar-stack"></div>
@@ -330,10 +330,6 @@ <h2 id="modal-title">New Squad</h2>
           这个 squad 的 agent 接到开发任务时会在此目录下创建 worktree。留空 = 纯讨论型 squad。
         </small>
       </label>
-      <label>Project directory
-        <input name="project_dir" id="squad-project-dir" autocomplete="off" spellcheck="false" class="mono" placeholder="/Volumes/DevDisk/symbol/openforge" />
-        <small class="field-hint" id="squad-project-dir-helper" aria-live="polite">这个 squad 的 agent 接到开发任务时会在此目录下创建 worktree。留空 = 纯讨论型 squad。</small>
-      </label>
       <label>Emoji<input name="emoji" maxlength="8" placeholder="✨" /></label>
       <fieldset>
         <legend>Members</legend>