[Plugin] Preserve handler errors in invocation-end hooks when returning PENDING #772

Expected behavior

When a handler raises an error and checkpoint-token withdrawal requires a PENDING response, the invocation-end hook should retain the original error details in InvocationEndInfo.error. Its status should remain PENDING.

The service response must remain exactly {"Status": "PENDING"}. It must contain neither Error nor Result. Ordinary suspension without a handler error should continue to report error=None.

Actual behavior

The revoked-token branches replace handler errors with an error-free pending output in execution.py:449–463.

The plugin wrapper reconstructs its invocation output from that service-response dictionary in plugin.py:845–851. So the invocation-end hook receives PENDING without the handler error.

JavaScript separates these outputs. Its answerPending implementation, with-durable-execution.ts:184–198, forwards executionError to plugins but returns bare PENDING to the service.

Reproduction scenario

1. Register a plugin that records the invocation-end status and error.
2. Invoke a handler that raises ValueError("handler failed").
3. Arrange for checkpoint-token withdrawal before the wrapper handles that exception.
4. Inspect the hook payload and returned dictionary.

The dictionary is bare PENDING, as required. The hook error is None, so the handler failure details are lost.

This scenario follows from source inspection at Python revision 52b63b5f; it has not been executed for this report.

Acceptance criteria

• Preserve the original handler error details in exactly one PENDING invocation-end notification.
• Keep the service response exactly {"Status": "PENDING"}.
• Keep suspension without a handler error free of fabricated errors.
• Add unit coverage that checks the hook payload and service response together.
• Add an end-to-end regression for the handler-to-plugin path.
• Preserve existing success, failure, and retry behavior.

Context

Follow-up to PR #757’s plugin-error parity discussion.