diff --git a/yunke-server/app/api/routers/sessions.py b/yunke-server/app/api/routers/sessions.py
index 7954dce..ab1d6ef 100644
--- a/yunke-server/app/api/routers/sessions.py
+++ b/yunke-server/app/api/routers/sessions.py
@@ -94,13 +94,14 @@ async def list_sessions(
     session: SessionDep,
     owner_account_id: Annotated[str, Query(min_length=1)],
     channel: Annotated[str, Query()] = "wechat",
-    is_del: Annotated[int | None, Query()] = None,
+    is_del: Annotated[int | None, Query(ge=0, le=1)] = None,
 ) -> SessionListOut:
     """账号会话列表:好友(talker_id,room_id 空)+ 群(room_id),按 last_chat_time desc。
 
     ``is_del`` 可选过滤(对齐云客员工聊天窗口「删除好友」开关):按 customer.delete_flag
-    在 Python 侧过滤——0=未删(NULL 视为 0),1=已删;无 customer 行的 talker(如
-    filehelper 等系统账号)视作未删保留;群会话不受该过滤影响。不传时行为不变。
+    在 Python 侧过滤——0=未删(NULL 视为 0),1=已删;越界值(非 0/1)422 拒绝而非
+    静默空列表;无 customer 行的 talker(如 filehelper 等系统账号)视作未删保留;
+    群会话不受该过滤影响。不传时行为不变。
     ``pinned``:filehelper 会话置顶标记(对齐云客置顶区),其余好友/群恒 False。
     """
     today_start = _today_start_ms()
diff --git a/yunke-server/tests/test_api_sessions.py b/yunke-server/tests/test_api_sessions.py
index 5f3183b..451ef34 100644
--- a/yunke-server/tests/test_api_sessions.py
+++ b/yunke-server/tests/test_api_sessions.py
@@ -95,10 +95,20 @@ async def test_sessions_is_del_filter(make_client):
     client = await make_client(seed)
     live = await client.get("/api/sessions", params={"owner_account_id": OWNER, "channel": CH, "is_del": 0})
     deleted = await client.get("/api/sessions", params={"owner_account_id": OWNER, "channel": CH, "is_del": 1})
-    assert live.status_code == 200 and deleted.status_code == 200
+    omitted = await client.get("/api/sessions", params={"owner_account_id": OWNER, "channel": CH})
+    assert live.status_code == 200 and deleted.status_code == 200 and omitted.status_code == 200
     # NULL 视为未删;无 customer 行的 talker 保留
     assert sorted(s["talker_id"] for s in live.json()["sessions"]) == ["f1", "filehelper", "gh0st"]
     assert [s["talker_id"] for s in deleted.json()["sessions"]] == ["f2"]
+    # 省略 is_del = 完全不过滤(显式契约:4 个 talker 全返回)
+    assert sorted(s["talker_id"] for s in omitted.json()["sessions"]) == ["f1", "f2", "filehelper", "gh0st"]
+
+
+async def test_sessions_is_del_out_of_range(make_client):
+    """``is_del`` 越界(如 2)→ 422,而非静默空列表。"""
+    client = await make_client(_seed)
+    r = await client.get("/api/sessions", params={"owner_account_id": OWNER, "channel": CH, "is_del": 2})
+    assert r.status_code == 422
 
 
 async def test_sessions_pinned_filehelper(make_client):