fix(agent): address session and streaming concurrency bugs

tests/providers/test_provider_retry.py

@@ -21,6 +21,17 @@ class ScriptedProvider(LLMProvider):
             raise response
         return response
 
+    async def chat_stream(self, *args, **kwargs) -> LLMResponse:
+        self.calls += 1
+        self.last_kwargs = kwargs
+        response = self._responses.pop(0)
+        if isinstance(response, BaseException):
+            raise response
+        delta = getattr(response, "_test_stream_delta", None)
+        if delta and kwargs.get("on_content_delta"):
+            await kwargs["on_content_delta"](delta)
+        return response
+
     def get_default_model(self) -> str:
         return "test-model"
 
@@ -122,6 +133,36 @@ async def test_chat_with_retry_preserves_cancelled_error() -> None:
         await provider.chat_with_retry(messages=[{"role": "user", "content": "hello"}])
 
 
+@pytest.mark.asyncio
+async def test_chat_stream_with_retry_does_not_retry_after_emitting_content(monkeypatch) -> None:
+    first = LLMResponse(content="stream stalled", finish_reason="error")
+    first._test_stream_delta = "partial"  # type: ignore[attr-defined]
+    provider = ScriptedProvider([
+        first,
+        LLMResponse(content="ok"),
+    ])
+    deltas: list[str] = []
+    delays: list[int] = []
+
+    async def _fake_sleep(delay: int) -> None:
+        delays.append(delay)
+
+    async def _on_delta(delta: str) -> None:
+        deltas.append(delta)
+
+    monkeypatch.setattr("nanobot.providers.base.asyncio.sleep", _fake_sleep)
+
+    response = await provider.chat_stream_with_retry(
+        messages=[{"role": "user", "content": "hello"}],
+        on_content_delta=_on_delta,
+    )
+
+    assert response.content == "stream stalled"
+    assert provider.calls == 1
+    assert deltas == ["partial"]
+    assert delays == []
+
+
 @pytest.mark.asyncio
 async def test_chat_with_retry_uses_provider_generation_defaults() -> None:
     """When callers omit generation params, provider.generation defaults are used."""