Module registry 

Global pending response registry for bidirectional communication

This module provides a global registry for pending bidirectional requests, enabling transports like MCP (which are fundamentally request-response) to route responses back to the correct BidirChannel.

Architecture

1. When a BidirChannel sends a request, it registers a callback in this registry
2. The transport (e.g., MCP) sends the request to the client as a notification
3. The client responds via a tool call (e.g., _plexus_respond)
4. The transport looks up the request in this registry and forwards the response
5. The registry callback deserializes and sends to the waiting BidirChannel

Thread Safety

The registry uses a RwLock for concurrent read access with exclusive write access. Registrations and lookups are fast; response handling is done outside the lock.

Functions

handle_pending_response

Handle a response for a pending request

is_request_pending

Check if a request is pending

pending_count

Get the count of pending requests (for monitoring/debugging)

register_pending_request

Register a pending request in the global registry

unregister_pending_request

Remove a pending request from the registry (e.g., on timeout)