fix: emit connection error asynchronously to avoid unhandled rejection crashes

[AmSach]

Summary

When a spawned server exits unexpectedly in stdio mode, the method synchronously calls on all pending request promises via . If no handler has been attached to those promises (or to ), the rejection fires before the caller's try/catch is active, and Node.js v15+ treats it as an unhandled rejection that calls , killing the entire process.

This was reported in issue modelcontextprotocol#1049 where using with a server that exits immediately causes to crash the Node.js process.

Root Cause

In , calls synchronously in a block:

When the stdio child process exits unexpectedly:

1. emits its event
2. is called
3. It rejects all pending request promises synchronously
4. If the caller hasn't attached yet, Node.js fires

Fix

Added a new registration API on the class:

1. ** Set** — stores registered error handlers
2. **** — registers a handler, returns a cleanup function
3. **** — emits the error **asynchronously via **, giving callers a chance to attach before the rejection fires

The defer means:

• Caller can do and the catch will fire
• Or caller can register to handle disconnections gracefully

API Usage

Files Changed

• : Added Set, method, method, and call to in

Closes modelcontextprotocol#1049