fix: robust Retry-After extraction across provider backends

tests/providers/test_provider_retry_after_hints.py

@@ -0,0 +1,42 @@
+from types import SimpleNamespace
+
+from nanobot.providers.anthropic_provider import AnthropicProvider
+from nanobot.providers.azure_openai_provider import AzureOpenAIProvider
+from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+
+def test_openai_compat_error_captures_retry_after_from_headers() -> None:
+    err = Exception("boom")
+    err.doc = None
+    err.response = SimpleNamespace(
+        text='{"error":{"message":"Rate limit exceeded"}}',
+        headers={"Retry-After": "20"},
+    )
+
+    response = OpenAICompatProvider._handle_error(err)
+
+    assert response.retry_after == 20.0
+
+
+def test_azure_openai_error_captures_retry_after_from_headers() -> None:
+    err = Exception("boom")
+    err.body = {"message": "Rate limit exceeded"}
+    err.response = SimpleNamespace(
+        text='{"error":{"message":"Rate limit exceeded"}}',
+        headers={"Retry-After": "20"},
+    )
+
+    response = AzureOpenAIProvider._handle_error(err)
+
+    assert response.retry_after == 20.0
+
+
+def test_anthropic_error_captures_retry_after_from_headers() -> None:
+    err = Exception("boom")
+    err.response = SimpleNamespace(
+        headers={"Retry-After": "20"},
+    )
+
+    response = AnthropicProvider._handle_error(err)
+
+    assert response.retry_after == 20.0