[parveensania]

Addresses #34705
R: @scwhittle

Description

• Adds ErrorReason (ERROR_REASON_UNSPECIFIED, CANCELLED) to StateResponse in beam_fn_api.proto to distinguish runner-initiated work item cancellations (e.g. during autoscaling or load-balancing) from unexpected state errors.
• When StateResponse.error_reason == CANCELLED, skips ERROR logging and logs at INFO level in SdkHarness._execute while still returning InstructionResponse.error to the runner.

Next Steps:

• Server-side runner changes and Java SDK implementation will follow in subsequently.

[github-actions]

Assigning reviewers:

R: @shunping for label python.

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[scwhittle]

Thanks! The approach looks good to me, but I will let someone more famliar with Python SDK to approve implementation specifics.

[shunping]

LGTM. Thanks!