Expose generic SendNotification on ServerSession for custom protocol extensions #745

Use Case

I am implementing an MCP Server for the Gemini CLI IDE Integration. The specification requires the server to send custom notifications to the client to signal specific events.

Specifically, I need to send:

• ide/diffAccepted
• ide/diffRejected
• ide/contextUpdate

The Problem

Currently, the mcp.ServerSession struct only exposes specific notification helpers (like NotifyProgress and Log). There is no public API to send a generic/custom JSON-RPC notification.

I attempted to use session.Notify(ctx, method, params), but:

1. The conn field on ServerSession is unexported.
2. The mcp.Connection interface's Write method requires *mcp.JSONRPCMessage, which is an unexported struct.

Proposed Solution

Please expose a generic notification method on ServerSession, similar to:

// In mcp/server.go

func (s *ServerSession) SendNotification(ctx context.Context, method string, params any) error {
    return s.conn.Notify(ctx, method, params)
}

Current Workaround

I am currently forced to use unsafe and reflect to access the underlying conn field to call its Notify method, which is fragile for obvious reasons.