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/agents/test_chat_agent_overflow_retry.py

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+"""
+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.
+"""
+
+import asyncio
+from types import SimpleNamespace
+from typing import List
+
+import pytest
+
+from app.agents.chat_agent import ChatAgent
+from app.agents.history_memory import BoundedHistoryMemory
+
+OVERFLOW = Exception(
+    "This model's maximum context length is 128000 tokens. However, your messages resulted in 145155 tokens"
+)
+
+
+class _FakeAgent:
+    """Stands in for the agno Agent: each arun() consumes the next outcome and
+    records the history budget in force at that moment."""
+
+    def __init__(self, outcomes: List):
+        self.outcomes = list(outcomes)
+        self.memory = BoundedHistoryMemory()
+        self.calls = 0
+        self.budgets: List[int] = []
+
+    async def arun(self, **kwargs):
+        self.calls += 1
+        self.budgets.append(getattr(self.memory, "history_max_chars", None))
+        outcome = self.outcomes.pop(0)
+        if isinstance(outcome, BaseException):
+            raise outcome
+        return outcome
+
+
+def _chat_agent(outcomes: List) -> ChatAgent:
+    shell = ChatAgent.__new__(ChatAgent)
+    shell.agent = _FakeAgent(outcomes)
+    return shell
+
+
+@pytest.mark.asyncio
+async def test_overflow_retries_once_without_history_then_restores_budget():
+    shell = _chat_agent([OVERFLOW, "ok"])
+    assert await shell._arun("hi", "s1") == "ok"
+    assert shell.agent.calls == 2
+    assert shell.agent.budgets[1] == 0
+    assert shell.agent.memory.history_max_chars > 0
+
+
+@pytest.mark.asyncio
+async def test_other_errors_are_not_retried():
+    shell = _chat_agent([Exception("rate limit exceeded")])
+    with pytest.raises(Exception, match="rate limit"):
+        await shell._arun("hi", "s1")
+    assert shell.agent.calls == 1
+
+
+@pytest.mark.asyncio
+async def test_second_overflow_surfaces():
+    shell = _chat_agent([OVERFLOW, OVERFLOW])
+    with pytest.raises(Exception, match="maximum context length"):
+        await shell._arun("hi", "s1")
+    assert shell.agent.calls == 2
+
+
+@pytest.mark.asyncio
+async def test_timeout_is_not_retried():
+    shell = _chat_agent([asyncio.TimeoutError()])
+    with pytest.raises(asyncio.TimeoutError):
+        await shell._arun("hi", "s1")
+    assert shell.agent.calls == 1
+
+
+@pytest.mark.asyncio
+async def test_plain_memory_is_not_retried():
+    shell = _chat_agent([OVERFLOW])
+    shell.agent.memory = SimpleNamespace()
+    with pytest.raises(Exception, match="maximum context length"):
+        await shell._arun("hi", "s1")
+    assert shell.agent.calls == 1