fix: prevent retry amplification by disabling SDK retries

tests/providers/test_provider_sdk_retry_defaults.py

@@ -0,0 +1,20 @@
+from unittest.mock import patch
+
+from nanobot.providers.anthropic_provider import AnthropicProvider
+from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+
+def test_openai_compat_disables_sdk_retries_by_default() -> None:
+    with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI") as mock_client:
+        OpenAICompatProvider(api_key="sk-test", default_model="gpt-4o")
+
+    kwargs = mock_client.call_args.kwargs
+    assert kwargs["max_retries"] == 0
+
+
+def test_anthropic_disables_sdk_retries_by_default() -> None:
+    with patch("anthropic.AsyncAnthropic") as mock_client:
+        AnthropicProvider(api_key="sk-test", default_model="claude-sonnet-4-5")
+
+    kwargs = mock_client.call_args.kwargs
+    assert kwargs["max_retries"] == 0