bug(ui): cancelling assistant response while processing message

[andrewrisse]

If you cancel an assistant response while the message is processing and you still have a loading skeleton, the skeleton never goes away.

This is because the backend creates a message with empty text initially, which triggers the skeleton to show up, but when you cancel, the message never gets filled in.

Ensure the message gets deleted on the backend, and confirm behavior with chat gpt. If the message is deleted, then the frontend needs to handle this someone. If it is not deleted by the backend, then either the backend needs to be fixed to delete it, or we should handle it properly on the frontend.