Allow customizable reconnection behavior for non-persistent clients #1162

Summary

The _scheduleReconnection method in StreamableHTTPClientTransport is currently private and uses setTimeout for scheduling reconnection attempts. This doesn't work well for clients that aren't running continuously (e.g., serverless functions, mobile apps that need push notifications to wake up).

Motivation

From PR #1129 review comment by @mattzcarey:

not for this PR but it would be good to be able to overwrite this method. For clients which aren't running all the time this will need some input externally from the client itself to wake it up.

Proposed Solution

Make reconnection behavior customizable, either by:

1. Allowing _scheduleReconnection to be overridden (make it protected or provide a hook)
2. Accepting a custom scheduler function in the transport options
3. Emitting an event when reconnection is needed, letting the client handle scheduling

Use Cases

• Serverless/edge functions that can't maintain long-running timers
• Mobile apps that need to schedule reconnection via platform-specific mechanisms (push notifications, background fetch)
• Desktop apps that need to handle sleep/wake cycles

Related

• PR feat: implement SEP-1699 SSE polling via server-side disconnect #1129: SEP-1699 SSE polling implementation