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/knowledge/test_failure_advice.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.
+
+A failed source's stored error becomes one plain sentence about "This site".
+"""
+
+import pytest
+
+from app.knowledge.failure_advice import FAILURE_ADVICE, GENERIC_REASON, plain_reason
+
+URL = "https://erfanpv.com"
+
+
+@pytest.mark.parametrize("cause", list(FAILURE_ADVICE))
+def test_our_advice_is_rephrased_about_this_site(cause):
+    reason = plain_reason(FAILURE_ADVICE[cause].format(url=URL), URL)
+    assert reason.startswith("This site ")
+    assert URL not in reason
+
+
+@pytest.mark.parametrize("error,source", [
+    ("Traceback (most recent call last): KeyError 'x'", URL),
+    (FAILURE_ADVICE[next(iter(FAILURE_ADVICE))].format(url="https://other.com"), URL),
+    (None, URL),
+    ("", URL),
+    ("anything", None),
+])
+def test_anything_else_gets_the_generic_reason(error, source):
+    assert plain_reason(error, source) == GENERIC_REASON