Persist heartbeat child pid before stdin handoff

packages/adapter-utils/src/server-utils.test.ts

@@ -0,0 +1,38 @@
+import { randomUUID } from "node:crypto";
+import { describe, expect, it } from "vitest";
+import { runChildProcess } from "./server-utils.js";
+
+describe("runChildProcess", () => {
+  it("waits for onSpawn before sending stdin to the child", async () => {
+    const spawnDelayMs = 150;
+    const startedAt = Date.now();
+    let onSpawnCompletedAt = 0;
+
+    const result = await runChildProcess(
+      randomUUID(),
+      process.execPath,
+      [
+        "-e",
+        "let data='';process.stdin.setEncoding('utf8');process.stdin.on('data',chunk=>data+=chunk);process.stdin.on('end',()=>process.stdout.write(data));",
+      ],
+      {
+        cwd: process.cwd(),
+        env: {},
+        stdin: "hello from stdin",
+        timeoutSec: 5,
+        graceSec: 1,
+        onLog: async () => {},
+        onSpawn: async () => {
+          await new Promise((resolve) => setTimeout(resolve, spawnDelayMs));
+          onSpawnCompletedAt = Date.now();
+        },
+      },
+    );
+    const finishedAt = Date.now();
+
+    expect(result.exitCode).toBe(0);
+    expect(result.stdout).toBe("hello from stdin");
+    expect(onSpawnCompletedAt).toBeGreaterThanOrEqual(startedAt + spawnDelayMs);
+    expect(finishedAt - startedAt).toBeGreaterThanOrEqual(spawnDelayMs);
+  });
+});