diff --git a/frontends/fsapp.py b/frontends/fsapp.py
index ad959f660..7dfb59d29 100644
--- a/frontends/fsapp.py
+++ b/frontends/fsapp.py
@@ -702,18 +702,22 @@ def fail(self, msg):
             self._fallback_text(f"❌ {msg}", final=True)
 
 
-def _make_task_hook(card, task_id, on_final):
-    """飞书任务 hook：每轮 patch 卡片状态；结束触发 on_final(raw) 处理附件。"""
+def _make_task_hook(card, task_id):
+    """飞书任务 hook：每轮用 summary patch 卡片状态；不触发 task 完成。
+
+    Finalization intentionally lives on the display-queue `done` item (and the
+    timeout/stop/exception paths in ``run_agent``), not on a turn-level
+    ``exit_reason`` from the agent. A turn-level exit_reason can fire on an
+    intermediate turn and would otherwise finalize the queued task before the
+    queue publishes its real ``done`` item, leaving the card marked complete
+    with the wrong text. See #685.
+    """
     def hook(ctx):
         try:
             parent = getattr(ctx.get("self"), "parent", None)
             if getattr(parent, "_fs_active_task_id", None) != task_id:
                 return
-            if ctx.get('exit_reason'):
-                resp = ctx.get('response')
-                raw = resp.content if hasattr(resp, 'content') else str(resp)
-                on_final(raw)
-            elif ctx.get('summary'):
+            if ctx.get('summary'):
                 detail = _build_step_detail(ctx.get('response'), ctx.get('tool_calls') or [])
                 card.step(ctx['summary'], detail)
         except Exception as e:
@@ -761,7 +765,7 @@ def _finish(raw):
             await asyncio.to_thread(card.start)
             if not hasattr(self.agent, '_turn_end_hooks'):
                 self.agent._turn_end_hooks = {}
-            self.agent._turn_end_hooks[hook_key] = _make_task_hook(card, task_id, _finish)
+            self.agent._turn_end_hooks[hook_key] = _make_task_hook(card, task_id)
             self.agent._fs_active_task_id = task_id
             dq = self.agent.put_task(f"{FILE_HINT}\n\n{text}", source=self.source, images=images or None)
             start = time.time()
diff --git a/tests/test_fsapp_exit_reason_no_finalize.py b/tests/test_fsapp_exit_reason_no_finalize.py
new file mode 100644
index 000000000..a5c7ec205
--- /dev/null
+++ b/tests/test_fsapp_exit_reason_no_finalize.py
@@ -0,0 +1,314 @@
+"""Regression test for #685.
+
+Before fix: ``_make_task_hook`` invoked the ``on_final`` callback whenever a hook
+context carried a truthy ``exit_reason``. Because ``run_agent`` passes ``_finish``
+as ``on_final``, an intermediate turn-level ``exit_reason`` could mark the queued
+task complete (``result["sent"] = True``) before the display queue published its
+real ``{"done": ...}`` item.
+
+After fix: the hook only patches the per-turn card step from ``summary``.
+Finalization happens only on the display-queue ``done`` item or on
+timeout/stop/exception paths in ``run_agent``.
+
+These tests load ``_make_task_hook`` and its pure helpers from the real
+``frontends/fsapp.py`` AST so we exercise the actual source rather than a
+copy. Heavy lark_oapi / agentmain / chatapp_common imports are skipped by
+extracting only the relevant function source via ast.parse.
+"""
+
+import ast
+import os
+import sys
+import types
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+FSAPP_PATH = REPO_ROOT / "frontends" / "fsapp.py"
+
+
+def _load_fsapp_helpers():
+    """Load ``_make_task_hook``, ``_display_text``, ``_build_step_detail``,
+    ``_fmt_tool_call`` from frontends/fsapp.py by AST-extracting their
+    source and exec'ing it in a fresh namespace. Heavy top-level imports
+    (lark_oapi, agentmain, chatapp_common) are skipped entirely.
+
+    The function source is taken verbatim from fsapp.py and re-executed in
+    a small namespace that provides ``_TRUNC_TAIL``, ``re``, ``json``,
+    ``getattr`` (builtin). The hooks are then re-bound to the module under
+    test using a lightweight fake ``_build_step_detail`` so we don't need
+    the full helper stack just to exercise the hook's dispatch logic.
+    """
+
+    src = FSAPP_PATH.read_text(encoding="utf-8")
+    tree = ast.parse(src)
+
+    # Collect the function source strings we need.
+    wanted = {"_display_text", "_build_step_detail", "_make_task_hook", "_fmt_tool_call", "_strip_files", "_clean"}
+    extracted = {}
+    for node in tree.body:
+        if isinstance(node, ast.FunctionDef) and node.name in wanted:
+            extracted[node.name] = ast.get_source_segment(src, node)
+
+    if "_make_task_hook" not in extracted:
+        raise RuntimeError("could not AST-extract _make_task_hook from fsapp.py")
+
+    # Build a small namespace with the bare-minimum helpers for the
+    # pure-function dependencies. We intentionally keep `_build_step_detail`
+    # as a no-op stub because the hook only uses it as a callback name; the
+    # behavior we care about (finalize vs not finalize) doesn't depend on
+    # the detail body.
+    ns = {
+        "re": __import__("re"),
+        "json": __import__("json"),
+        "_TRUNC_TAIL": 200,
+    }
+
+    # Stub out pure-function dependencies that are safe to skip.
+    exec(
+        "def _display_text(text):\n"
+        "    return (text or '').strip() or '⚠️ 模型输出被截断或为空'\n",
+        ns,
+    )
+    exec(
+        "def _build_step_detail(resp, tool_calls):\n"
+        "    return ''\n",
+        ns,
+    )
+    # Now exec the real _make_task_hook source into the namespace.
+    exec(extracted["_make_task_hook"], ns)
+    return ns
+
+
+def _make_fake_card():
+    card = types.SimpleNamespace()
+    card.step_calls = []
+    card.done_calls = []
+    card.fail_calls = []
+
+    def step(summary, detail=""):
+        card.step_calls.append((summary, detail))
+
+    def done(text):
+        card.done_calls.append(text)
+
+    def fail(msg):
+        card.fail_calls.append(msg)
+
+    card.step = step
+    card.done = done
+    card.fail = fail
+    return card
+
+
+def _make_fake_parent(task_id):
+    parent = types.SimpleNamespace()
+    parent._fs_active_task_id = task_id
+    return parent
+
+
+# A wrapper class whose instances carry `_fs_active_task_id`. We do this
+# rather than passing the parent directly because the hook reads
+# `ctx.get("self").parent` -- i.e. it expects ``ctx["self"]`` to be an object
+# whose attribute ``parent`` is the active-task holder. Mirrors how the real
+# agent_loop passes the loop self into the hook ctx.
+class _LoopSelf:
+    def __init__(self, parent):
+        self.parent = parent
+
+
+def _ctx_for(task_id, **fields):
+    parent = _make_fake_parent(task_id)
+    return {"self": _LoopSelf(parent), **fields}
+
+
+def test_hook_does_not_finalize_on_exit_reason_with_response():
+    """#685 case 1: a turn-level exit_reason with a response must not call on_final."""
+    ns = _load_fsapp_helpers()
+    card = _make_fake_card()
+    task_id = "fs_test_task_1"
+
+    hook = ns["_make_task_hook"](card, task_id)
+
+    class _Resp:
+        content = "intermediate turn text"
+
+    ctx = _ctx_for(
+        task_id,
+        exit_reason={"result": "CURRENT_TASK_DONE", "data": None},
+        response=_Resp(),
+    )
+    hook(ctx)
+
+    assert card.done_calls == [], (
+        f"hook finalized the task on turn-level exit_reason "
+        f"(#685 regression): done_calls={card.done_calls!r}"
+    )
+    assert card.step_calls == [], (
+        f"hook added a step when only exit_reason was present (no summary): "
+        f"step_calls={card.step_calls!r}"
+    )
+
+
+def test_hook_adds_step_when_summary_present_with_exit_reason():
+    """#685 case 2: when both summary and exit_reason are present, summary wins."""
+    ns = _load_fsapp_helpers()
+    card = _make_fake_card()
+    task_id = "fs_test_task_2"
+
+    hook = ns["_make_task_hook"](card, task_id)
+
+    class _Resp:
+        content = "wrote file output"
+        thinking = "I did the thing."
+
+    ctx = _ctx_for(
+        task_id,
+        summary="wrote file",
+        exit_reason={"result": "EXITED", "data": None},
+        response=_Resp(),
+        tool_calls=[],
+    )
+    hook(ctx)
+
+    assert len(card.step_calls) == 1, (
+        f"summary must be added as a step even when exit_reason is also "
+        f"present: step_calls={card.step_calls!r}"
+    )
+    assert card.step_calls[0][0] == "wrote file", card.step_calls
+    assert card.done_calls == [], (
+        f"hook must not finalize the task on exit_reason even when a "
+        f"summary is also present: done_calls={card.done_calls!r}"
+    )
+
+
+def test_hook_adds_step_for_summary_only():
+    ns = _load_fsapp_helpers()
+    card = _make_fake_card()
+    task_id = "fs_test_task_3"
+
+    hook = ns["_make_task_hook"](card, task_id)
+
+    class _Resp:
+        content = "answer"
+        thinking = ""
+
+    ctx = _ctx_for(
+        task_id,
+        summary="answered",
+        response=_Resp(),
+        tool_calls=[],
+    )
+    hook(ctx)
+
+    assert len(card.step_calls) == 1
+    assert card.step_calls[0][0] == "answered"
+    assert card.done_calls == []
+
+
+def test_hook_is_no_op_for_stale_task_id():
+    ns = _load_fsapp_helpers()
+    card = _make_fake_card()
+    task_id = "fs_test_task_4"
+    # parent._fs_active_task_id deliberately mismatches task_id.
+
+    hook = ns["_make_task_hook"](card, task_id)
+
+    ctx = _ctx_for(
+        task_id,
+        summary="should be ignored",
+        exit_reason={"result": "EXITED"},
+    )
+    # Overwrite parent._fs_active_task_id so the guard fires.
+    ctx["self"].parent._fs_active_task_id = "some_other_task"
+
+    hook(ctx)
+
+    assert card.step_calls == []
+    assert card.done_calls == []
+
+
+def test_hook_signature_no_longer_takes_on_final():
+    """The fix removes ``on_final`` from the public hook signature."""
+    import inspect
+
+    ns = _load_fsapp_helpers()
+    sig = inspect.signature(ns["_make_task_hook"])
+    params = list(sig.parameters)
+    assert params == ["card", "task_id"], (
+        f"unexpected hook signature after fix: {params}; on_final must be "
+        f"removed (finalization belongs on the display-queue done item)."
+    )
+
+
+def test_old_signature_would_have_finalized_on_exit_reason():
+    """Reproduce the pre-fix behavior at the source level so we cover the
+    behavioral bug, not only the signature change. This loads the
+    pre-fix version of ``_make_task_hook`` (3 args: card, task_id, on_final)
+    and asserts that calling it with an exit_reason-only context WOULD
+    have triggered the (now-removed) on_final callback. The post-fix
+    source no longer accepts on_final, so we exercise the OLD source via
+    an inline reproduction.
+    """
+    on_final_calls = []
+
+    def on_final(raw):
+        on_final_calls.append(raw)
+
+    # This is the OLD _make_task_hook body, copied verbatim from the
+    # unfixed fsapp.py to capture the behavioral regression. If the live
+    # _make_task_hook in fsapp.py ever regains an on_final branch, this
+    # test stays meaningful as a behavioral pin.
+    def old_hook_factory(card, task_id, on_final):
+        def hook(ctx):
+            parent = getattr(ctx.get("self"), "parent", None)
+            if getattr(parent, "_fs_active_task_id", None) != task_id:
+                return
+            if ctx.get("exit_reason"):
+                resp = ctx.get("response")
+                raw = resp.content if hasattr(resp, "content") else str(resp)
+                on_final(raw)
+            elif ctx.get("summary"):
+                pass  # would have called card.step
+        return hook
+
+    card = _make_fake_card()
+
+    class _Resp:
+        content = "intermediate turn text"
+
+    ctx = _ctx_for(
+        "fs_test_task_5",
+        exit_reason={"result": "EXITED"},
+        response=_Resp(),
+    )
+    old_hook_factory(card, "fs_test_task_5", on_final)(ctx)
+
+    # Sanity: confirms that the OLD signature's exit_reason branch DID
+    # call on_final. This is the exact behavior #685 reports and that the
+    # real fix removes. If this assertion ever fails (i.e. on_final is
+    # NOT called by the OLD hook) the regression test would no longer
+    # cover the bug — meaning either fsapp.py silently re-changed or the
+    # reproduction is wrong.
+    assert on_final_calls == ["intermediate turn text"], (
+        f"reproduction of pre-fix behavior is incorrect: "
+        f"on_final_calls={on_final_calls!r}"
+    )
+
+
+if __name__ == "__main__":
+    failures = 0
+    for name, fn in list(globals().items()):
+        if name.startswith("test_") and callable(fn):
+            try:
+                fn()
+                print(f"PASS {name}")
+            except AssertionError as e:
+                failures += 1
+                print(f"FAIL {name}: {e}")
+            except Exception as e:
+                failures += 1
+                print(f"ERROR {name}: {type(e).__name__}: {e}")
+    if failures:
+        sys.exit(1)
+    print("ALL PASS")