test: 补充知识处理、检索与 Agent 回归用例

覆盖切块、向量检索、工具调用和历史预算；模型相关用例使用桩。

backend/tests/test_migrations.py

@@ -0,0 +1,41 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from pathlib import Path
+
+from alembic.config import Config
+from alembic.script import ScriptDirectory
+
+BACKEND_DIR = Path(__file__).resolve().parents[1]
+
+
+def test_migrations_have_a_single_head():
+    """Two heads take production down: scripts/start.sh runs `alembic upgrade
+    head`, which refuses to choose between them, so the container exits before
+    gunicorn binds and restart-loops behind a 502.
+
+    It happens when two branches each add a revision off the same parent — each
+    PR is green alone and the branch only exists once both have merged, so
+    reviewing either in isolation cannot catch it. This can.
+
+    Fix by re-parenting the unapplied revision onto the other head (linear, no
+    merge revision), or with a merge revision when both have already been
+    applied somewhere.
+    """
+    heads = ScriptDirectory.from_config(
+        Config(str(BACKEND_DIR / "alembic.ini"))
+    ).get_heads()
+    assert len(heads) == 1, f"expected one migration head, found: {heads}"