Fix SSE client error handling and propagate API key in headers

[jfrench9]

Summary

This PR fixes bugs in the SSE client related to error handling and API key propagation. The SSE client was not properly handling error scenarios, and the API key was not being passed through in request headers, causing authentication failures during server-sent event connections.

Key Accomplishments

• Enhanced SSE client error handling: Added robust error handling logic to the SSE client to gracefully manage connection failures, malformed responses, and other error conditions during event streaming.
• API key header propagation: Fixed a bug where the API key was not being included in headers when establishing SSE connections through the operation client, ensuring authenticated access to event streams.
• Model correction: Updated the CreateEventHandlerRequest model to fix a field type/definition issue.
• Test coverage: Added comprehensive unit tests for the SSE client to validate error handling behavior and ensure regressions are caught.

Changes Breakdown

File	Change
operation_client.py	Extended with API key header propagation and improved SSE connection setup (~35 lines added)
sse_client.py	Added error handling logic for SSE stream consumption (~26 lines added)
create_event_handler_request.py	Minor model field fix
test_sse_client.py	New test cases for SSE client error scenarios (~35 lines added)

Breaking Changes

None. These changes are backward-compatible fixes that improve reliability without altering the public API surface.

Testing Notes

• New unit tests have been added in test_sse_client.py covering error handling paths in the SSE client.
• Verify that SSE connections properly authenticate using the API key in environments where authentication is required.
• Test SSE reconnection and error recovery scenarios in integration/staging environments to confirm graceful degradation under network instability.

Infrastructure Considerations

• Ensure that any API gateway or proxy configurations allow the API key header to pass through on SSE/long-lived HTTP connections.
• Monitor SSE connection error rates after deployment to validate the improved error handling reduces silent failures.

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Branch Info:

• Source: bugfix/sse-client-bug
• Target: main
• Type: bugfix

Co-Authored-By: Claude noreply@anthropic.com