refactor(llm): share transient retry across agent paths

tests/test_provider_retry.py

@@ -0,0 +1,92 @@
+import asyncio
+
+import pytest
+
+from nanobot.providers.base import LLMProvider, LLMResponse
+
+
+class ScriptedProvider(LLMProvider):
+    def __init__(self, responses):
+        super().__init__()
+        self._responses = list(responses)
+        self.calls = 0
+
+    async def chat(self, *args, **kwargs) -> LLMResponse:
+        self.calls += 1
+        response = self._responses.pop(0)
+        if isinstance(response, BaseException):
+            raise response
+        return response
+
+    def get_default_model(self) -> str:
+        return "test-model"
+
+
+@pytest.mark.asyncio
+async def test_chat_with_retry_retries_transient_error_then_succeeds(monkeypatch) -> None:
+    provider = ScriptedProvider([
+        LLMResponse(content="429 rate limit", finish_reason="error"),
+        LLMResponse(content="ok"),
+    ])
+    delays: list[int] = []
+
+    async def _fake_sleep(delay: int) -> None:
+        delays.append(delay)
+
+    monkeypatch.setattr("nanobot.providers.base.asyncio.sleep", _fake_sleep)
+
+    response = await provider.chat_with_retry(messages=[{"role": "user", "content": "hello"}])
+
+    assert response.finish_reason == "stop"
+    assert response.content == "ok"
+    assert provider.calls == 2
+    assert delays == [1]
+
+
+@pytest.mark.asyncio
+async def test_chat_with_retry_does_not_retry_non_transient_error(monkeypatch) -> None:
+    provider = ScriptedProvider([
+        LLMResponse(content="401 unauthorized", finish_reason="error"),
+    ])
+    delays: list[int] = []
+
+    async def _fake_sleep(delay: int) -> None:
+        delays.append(delay)
+
+    monkeypatch.setattr("nanobot.providers.base.asyncio.sleep", _fake_sleep)
+
+    response = await provider.chat_with_retry(messages=[{"role": "user", "content": "hello"}])
+
+    assert response.content == "401 unauthorized"
+    assert provider.calls == 1
+    assert delays == []
+
+
+@pytest.mark.asyncio
+async def test_chat_with_retry_returns_final_error_after_retries(monkeypatch) -> None:
+    provider = ScriptedProvider([
+        LLMResponse(content="429 rate limit a", finish_reason="error"),
+        LLMResponse(content="429 rate limit b", finish_reason="error"),
+        LLMResponse(content="429 rate limit c", finish_reason="error"),
+        LLMResponse(content="503 final server error", finish_reason="error"),
+    ])
+    delays: list[int] = []
+
+    async def _fake_sleep(delay: int) -> None:
+        delays.append(delay)
+
+    monkeypatch.setattr("nanobot.providers.base.asyncio.sleep", _fake_sleep)
+
+    response = await provider.chat_with_retry(messages=[{"role": "user", "content": "hello"}])
+
+    assert response.content == "503 final server error"
+    assert provider.calls == 4
+    assert delays == [1, 2, 4]
+
+
+@pytest.mark.asyncio
+async def test_chat_with_retry_preserves_cancelled_error() -> None:
+    provider = ScriptedProvider([asyncio.CancelledError()])
+
+    with pytest.raises(asyncio.CancelledError):
+        await provider.chat_with_retry(messages=[{"role": "user", "content": "hello"}])