fix(test-utils): Prune old events from buffer when listener registers

Instead of just filtering old events, actually remove them from the buffer.
This prevents stale events from ever being matched by future listeners,
even if timestamps are somehow compared incorrectly.

Events older than the listener registration time are definitely stale
and will never be needed by any listener.

Author: BYK

dev-packages/e2e-tests/test-applications/nextjs-15-spotlight/package.json

@@ -14,7 +14,7 @@
     "@types/node": "^18.19.1",
     "@types/react": "18.0.26",
     "@types/react-dom": "18.0.9",
-    "next": "15.5.7",
+    "next": "15.5.9",
     "react": "latest",
     "react-dom": "latest",
     "typescript": "~5.0.0"

dev-packages/test-utils/src/event-proxy-server.ts

@@ -150,13 +150,16 @@ export async function startProxyServer(
 
     eventCallbackListeners.add(callbackListener);
 
-    // Use strict inequality to prevent stale events from previous tests leaking through.
-    // If a previous test's event was buffered at the same millisecond as this listener started,
-    // we want to exclude it.
+    // Prune old events from the buffer that are definitely stale (older than this listener).
+    // This prevents memory buildup and ensures old events can never leak to future listeners.
+    while (eventBuffer.length > 0 && eventBuffer[0].timestamp <= listenerTimestamp) {
+      eventBuffer.shift();
+    }
+
+    // Send any remaining buffered events (those that arrived after this listener was registered,
+    // which can happen due to race conditions with HTTP request processing).
     eventBuffer.forEach(bufferedEvent => {
-      if (bufferedEvent.timestamp > listenerTimestamp) {
-        callbackListener.callback(bufferedEvent.data);
-      }
+      callbackListener.callback(bufferedEvent.data);
     });
 
     eventCallbackRequest.on('close', () => {