[OliPetry]

Issue for this PR

Closes #20384

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Anthropic returns {"type":"overloaded_error","message":"Overloaded"} as a stream error when their API is at capacity. This was not recognized by the error handling pipeline, causing sessions to halt with a terminal error instead of retrying.

The root cause: parseStreamError() in error.ts only checked for body.type === "error", so "overloaded_error" fell through. The error became a NamedError.Unknown, and retryable() in retry.ts didn't match it either since its JSON fallback path only checked for type === "error" variants.

The fix adds overloaded_error handling in two places:

1. parseStreamError() — recognizes type: "overloaded_error" and returns it as a retryable api_error. Also widens ParsedStreamError.isRetryable from literal false to boolean so stream errors can be retryable.
2. retryable() fallback — adds json.type === "overloaded_error" check as a safety net for the JSON parsing path.

With this fix, overloaded errors trigger the existing exponential backoff retry logic (2s → 4s → 8s → 16s → 30s cap) instead of killing the session.

How did you verify your code works?

1. Traced the error flow manually from the raw Anthropic error through fromError() → parseStreamError() → retryable() confirming the classification bug
2. Verified the fix path: parseStreamError() now returns {type: "api_error", isRetryable: true}, which fromError() wraps as MessageV2.APIError, which retryable() matches at line 54-58 (existing isRetryable + "Overloaded" check)
3. Unit tests and typecheck pass

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

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[github-actions]

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[rekram1-node]

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