fix(server): clear keepalive timer before reassignment in replayEvents

Prevent timer handle leaks when concurrent reconnect requests bypass
the conflict check. This edge case is possible when EventStore omits the
optional getStreamIdForEventId method, allowing duplicate replay
attempts to start new timers without cleaning up existing ones.

Author: rcdailey

packages/server/src/server/streamableHttp.ts

@@ -587,6 +587,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
             // Start keepalive timer for the replayed stream so reconnecting
             // clients remain protected from proxy idle timeouts
             if (this._keepAliveInterval !== undefined) {
+                this._clearKeepAliveTimer();
                 this._keepAliveTimer = setInterval(() => {
                     try {
                         streamController!.enqueue(encoder.encode(': keepalive\n\n'));