FallbackChatClient: classify transport-level failures as transient#427
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The SDK retry policy can give up on a transport-level failure (DNS, TCP reset, "Resource temporarily unavailable") with "Retry failed after N tries." — no HTTP response is received, so ClientResultException.Status is 0 and HttpRequestException.StatusCode is null. The previous classifier required a known HTTP status code and mapped 0/null to Unknown, which re-throws immediately and skips the configured fallback model. Now Status==0 ClientResultException, null-StatusCode HttpRequestException, inner SocketException/IOException, and the "Retry failed after" / "temporarily unavailable" message wrappers all classify as Transient, so the Balanced tier actually falls through to OpenRouter when Azure's endpoint is unreachable. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
ClientResultExceptionwithStatus == 0(no HTTP response received). The previous classifier required a known HTTP status, mapped 0/null toUnknown, and re-threw immediately — so the Balanced tier never fell back to OpenRouter when Azure's endpoint was unreachable.ClassifyExceptionnow treats four previously-Unknown shapes asTransient:ClientResultExceptionwithStatus == 0HttpRequestExceptionwithStatusCode == nullSocketExceptionorIOException"Retry failed after"or"temporarily unavailable"(catch-all wrapper)Retry failed after 4 tries. (Resource temporarily unavailable (rocky-ml1nznjr-eastus2.cognitiveservices.azure.com:443))).Background
A subagent fan-out + synthesis run failed end-to-end against the Balanced-tier Azure endpoint with the message above. OpenRouter is configured as the Balanced fallback but was never tried — both the subagent's own LLM call and the synthesis call gave up after the SDK's internal retries, because
FallbackChatClientcouldn't recognize the resulting exception as transient.Test plan
dotnet test tests/RockBot.Llm.Tests/RockBot.Llm.Tests.csproj— 134/134 passFallbackChatClient: falling back from … to …) the next time Azure throttles the Balanced endpoint🤖 Generated with Claude Code