Describe the bug

When implementing a custom AI proxy for BlockNote using a Kotlin/Ktor backend that connects to the OpenAI API, the editor's AI functionality fails, showing the error: Error calling LLM Error: No operations seen.

This occurs when BlockNote communicates with the custom AI proxy endpoint. The proxy server correctly implements an OpenAI-compatible streaming response, returning Server-Sent Events (SSE) with a text/event-stream content type.

The error suggests that while the connection is successful, BlockNote's client-side module does not recognize the response format. The core issue seems to be a mismatch between the standard OpenAI stream format and the specific "operation" format that BlockNote expects to receive.

To Reproduce

1. Set up a backend server (e.g., using Kotlin/Ktor) to act as an AI proxy.
2. Configure the server to forward requests to the OpenAI API and stream the response back.
3. Implement the BlockNote editor in a frontend application.
4. Configure the BlockNote AI client to use the custom proxy URL
5. Attempt to use any AI feature in the BlockNote editor (e.g., text completion).
6. Observe the error Error calling LLM Error: No operations seen in the browser's developer console.

Misc

• Node version: v23.6.1
• Package manager: npm
• Browser: Version 137.0.7151.69 (Official Build) (arm64)