fix: use structured error metadata for app-layer retry

tests/providers/test_provider_error_metadata.py

@@ -0,0 +1,77 @@
+from types import SimpleNamespace
+
+from nanobot.providers.anthropic_provider import AnthropicProvider
+from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+
+def _fake_response(
+    *,
+    status_code: int,
+    headers: dict[str, str] | None = None,
+    text: str = "",
+) -> SimpleNamespace:
+    return SimpleNamespace(
+        status_code=status_code,
+        headers=headers or {},
+        text=text,
+    )
+
+
+def test_openai_handle_error_extracts_structured_metadata() -> None:
+    class FakeStatusError(Exception):
+        pass
+
+    err = FakeStatusError("boom")
+    err.status_code = 409
+    err.response = _fake_response(
+        status_code=409,
+        headers={"retry-after-ms": "250", "x-should-retry": "false"},
+        text='{"error":"conflict"}',
+    )
+    err.body = {"error": "conflict"}
+
+    response = OpenAICompatProvider._handle_error(err)
+
+    assert response.finish_reason == "error"
+    assert response.error_status_code == 409
+    assert response.error_retry_after_s == 0.25
+    assert response.error_should_retry is False
+
+
+def test_openai_handle_error_marks_timeout_kind() -> None:
+    class FakeTimeoutError(Exception):
+        pass
+
+    response = OpenAICompatProvider._handle_error(FakeTimeoutError("timeout"))
+
+    assert response.finish_reason == "error"
+    assert response.error_kind == "timeout"
+
+
+def test_anthropic_error_response_extracts_structured_metadata() -> None:
+    class FakeStatusError(Exception):
+        pass
+
+    err = FakeStatusError("boom")
+    err.status_code = 408
+    err.response = _fake_response(
+        status_code=408,
+        headers={"retry-after": "1.5", "x-should-retry": "true"},
+    )
+
+    response = AnthropicProvider._error_response(err)
+
+    assert response.finish_reason == "error"
+    assert response.error_status_code == 408
+    assert response.error_retry_after_s == 1.5
+    assert response.error_should_retry is True
+
+
+def test_anthropic_error_response_marks_connection_kind() -> None:
+    class FakeConnectionError(Exception):
+        pass
+
+    response = AnthropicProvider._error_response(FakeConnectionError("connection"))
+
+    assert response.finish_reason == "error"
+    assert response.error_kind == "connection"