Shutdown handler drops responses and violates LSP state machine

[meymchen]

Component

pygls/protocol/json_rpc.py

Summary

After receiving the shutdown request, _shutdown is set to True and handle_message rejects every subsequent message except exit. This includes responses from the client to requests that the server sent before shutdown (e.g., client/registerCapability, workspace/configuration). Per the LSP specification, the server must not exit until exit is received, and in-flight bidirectional communication must still be honored.

Steps to Reproduce

1. Server sends a request to the client (e.g., workspace/configuration).
2. Client sends shutdown before responding.
3. The server drops the client's response because _shutdown blocks it.
4. The internal Future associated with the request leaks and never resolves.

Expected Behavior

_handle_response should continue processing even after shutdown. Only new client requests/notifications (other than exit) should be ignored.

Actual Behavior

All messages except exit are dropped after shutdown.

Affected Code (pygls/protocol/json_rpc.py, ~L496-498)

if self._shutdown and getattr(message, "method", "") != EXIT:
    logger.warning("Server shutting down. No more requests!")
    return

Proposed Fix

Guard _handle_request and _handle_notification, but allow _handle_response to pass through regardless of the _shutdown flag.