MCPSessionManager

Set or validate the connection configs used by this manager.

When no sessions exist yet, connections overwrites the stored configs unconditionally. Once any session has been created, the new connections must produce the same signature as the stored ones — otherwise this raises to prevent rebinding live sessions to different transports or auth providers.

Return a cached session for server_name, creating it lazily.

Evict and close a cached session if it still matches expected_session.

Close all cached sessions concurrently and reject future creation.

Each server's exit_stack.aclose() runs with a 5 second timeout so one slow stdio server cannot stall shutdown. Per-server failures are logged — teardown is best-effort — but CancelledError is re-raised so the enclosing asyncio.gather still cancels peers.