fix: serialize local-agent heartbeats

local-agent/serialized-runner.mjs

@@ -0,0 +1,16 @@
+export function createSerializedRunner(task) {
+  let activePromise = null;
+
+  return function runSerialized(...args) {
+    if (activePromise) {
+      return activePromise;
+    }
+
+    activePromise = Promise.resolve(task(...args))
+      .finally(() => {
+        activePromise = null;
+      });
+
+    return activePromise;
+  };
+}

local-agent/server.mjs

@@ -7,6 +7,7 @@ import os from "node:os";
 import { join, resolve } from "node:path";
 import { discoverCodexProjectCandidatesInWorker } from "./codex-session-discovery.mjs";
 import { buildCodexTaskExecution } from "./codex-task-runner.mjs";
+import { createSerializedRunner } from "./serialized-runner.mjs";
 
 async function loadConfig(configPath) {
   const raw = await readFile(resolve(configPath), "utf8");
@@ -493,7 +494,7 @@ const runtime = {
   lastProjectDiscoverySummary: null,
 };
 
-async function heartbeat() {
+async function performHeartbeat() {
   try {
     const heartbeatProjects = await resolveHeartbeatProjects(config, runtime);
     const result = await postHeartbeat(config, runtime, heartbeatProjects);
@@ -567,6 +568,8 @@ async function heartbeat() {
   }
 }
 
+const heartbeat = createSerializedRunner(performHeartbeat);
+
 const server = createServer(async (request, response) => {
   if (request.url === "/health") {
     response.writeHead(200, { "Content-Type": "application/json" });

tests/local-agent-serialized-runner.test.mjs

@@ -0,0 +1,39 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { createSerializedRunner } from "../local-agent/serialized-runner.mjs";
+
+test("createSerializedRunner coalesces overlapping calls into the same promise", async () => {
+  let runs = 0;
+  let release;
+  const gate = new Promise((resolve) => {
+    release = resolve;
+  });
+
+  const runner = createSerializedRunner(async () => {
+    runs += 1;
+    await gate;
+    return { runs };
+  });
+
+  const first = runner();
+  const second = runner();
+  assert.equal(first, second);
+  assert.equal(runs, 1);
+
+  release();
+  const result = await first;
+  assert.deepEqual(result, { runs: 1 });
+});
+
+test("createSerializedRunner allows the next call after the current run finishes", async () => {
+  let runs = 0;
+  const runner = createSerializedRunner(async () => {
+    runs += 1;
+    return runs;
+  });
+
+  assert.equal(await runner(), 1);
+  assert.equal(await runner(), 2);
+  assert.equal(runs, 2);
+});