Support kernel_info request on the control channel

80-kernel-info/kernel-info.md

@@ -0,0 +1,40 @@
+# Send kernel\_info request on the control channel
+
+## Problem
+
+When connecting a new websocket to an existing kernel via the Jupyter server, if the kernel execution is
+stopped on a breakpoint, the messages sent over the websocket get no reply. This is because when
+establibshing a new websocket connection, the Jupyter server will send `kernel_info` requests to the kernel
+and will prevent sending any other request until it receives a `kernel_info` reply. Since the `kernel_info`
+request is sent on the shell channel and the kernel executino is stopped, it cannot reply to that request.
+
+## Proposed enhancement
+
+We propose to state in the Jupyter Messaging Protocol that the `kernel_info` request muter st be sent on the
+control channel exclusively.
+
+### Impact on existing implementations
+
+There should not be any impact on the existing kernels, since the current specification states that any message
+that can be sent on the shell channel could be sent on the control channel.
+
+The only impact of this change (beyond the protocol itself) is on the Jupyter Server, which must be updated
+accordingly.
+
+## Relevant Resources (GitHub repositories, Issues, PRs)
+
+### GitHub repositories
+
+- [Jupyter server](https://github.com/jupyter-server/jupyter_server): the backend to Jupyter web applications
+- [Jupyter client](https://github.com/jupyter/jupyter_client): Jupyter protocol client APIs
+- [JupyterLab](https://github.com/jupyterlab/jupyterlab): JupyterLab computational environment
+
+### GitHub Issues
+
+- New websocket unable to communicate with kernel paused in debugging [#622](https://github.com/jupyter-server/jupyter_server/issues/622)
+- [Debugger] Active sessions cause the kernel to deadlock on page refresh [#10174](https://github.com/jupyterlab/jupyterlab/issues/10174)
+
+### GitHub Pull Requests
+
+Nudge kernel with info request until we receive IOPub messages [#361](https://github.com/jupyter-server/jupyter_server/pull/361)
+