Description

✨ This PR introduces error handling for the streaming transport layer. It ensures that local and server-side errors are handled correctly, mirroring the existing behavior of the REST architecture while supporting the unique lifecycles required for subscriptions.

Changes

• Execution Errors: Updated the response handler to dynamically construct a failure response and reject execution promises with a typed DataConnectOperationError when an error payload is received from the server for queries or mutations.
• Message Send Failures: Added error catching logic to send*Message() to gracefully reject the associated execution promise if the local message transmission fails.
• Subscription Errors: Ensured that local transmission failures for subscriptions synthesize a mock response containing the error and pass it to the subscription's notification hook, allowing the Query layer to handle and broadcast the error. Server responses for subscriptions containing errors are correctly routed to hooks without spontaneously terminating the tracked stream.
• Tracking + Cleanup Refactorization: Consolidated request tracking and cleanup logic and now use promise callbacks to cleanup.

Testing

• Extended stream transport unit tests to verify that execution promises gracefully reject with a DataConnectOperationError upon receiving error payloads from the server.
• Added tests verifying that if a local message transmission fails for executions, the associated tracking maps are properly cleaned up.
• Added tests to ensure subscribe operations correctly call the notification hook with an error payload and successfully tear down tracking logic if the initial transmission fails.
• Confirmed that error responses for active subscriptions continue to be routed to the target hooks instead of throwing exceptions or prematurely cleaning the map.