fix: drop active heartbeat followups from queue (#25610, thanks @mcaxtr)

Co-authored-by: Marcus Castro <mcaxtr@gmail.com>

src/auto-reply/reply/agent-runner.ts

@@ -235,6 +235,11 @@ export async function runReplyAgent(params: {
     }
   }
 
+  if (isHeartbeat && isActive) {
+    typing.cleanup();
+    return undefined;
+  }
+
   if (isActive && (shouldFollowup || resolvedQueue.mode === "steer")) {
     enqueueFollowupRun(queueKey, followupRun, resolvedQueue);
     await touchActiveSessionEntry();