From 26d4cabb2e8a041f15fb1080f421c35777128c21 Mon Sep 17 00:00:00 2001
From: dotta <dotta@example.com>
Date: Wed, 8 Apr 2026 09:47:02 -0500
Subject: [PATCH] Persist heartbeat child pid before stdin handoff

---
 .../adapter-utils/src/server-utils.test.ts    | 38 +++++++++++++++++++
 packages/adapter-utils/src/server-utils.ts    | 25 +++++++-----
 2 files changed, 53 insertions(+), 10 deletions(-)
 create mode 100644 packages/adapter-utils/src/server-utils.test.ts

diff --git a/packages/adapter-utils/src/server-utils.test.ts b/packages/adapter-utils/src/server-utils.test.ts
new file mode 100644
index 00000000..62e395b0
--- /dev/null
+++ b/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);
+  });
+});
diff --git a/packages/adapter-utils/src/server-utils.ts b/packages/adapter-utils/src/server-utils.ts
index 1c6a2795..83dbe06f 100644
--- a/packages/adapter-utils/src/server-utils.ts
+++ b/packages/adapter-utils/src/server-utils.ts
@@ -1069,16 +1069,12 @@ export async function runChildProcess(
         }) as ChildProcessWithEvents;
         const startedAt = new Date().toISOString();
 
-        if (opts.stdin != null && child.stdin) {
-          child.stdin.write(opts.stdin);
-          child.stdin.end();
-        }
-
-        if (typeof child.pid === "number" && child.pid > 0 && opts.onSpawn) {
-          void opts.onSpawn({ pid: child.pid, startedAt }).catch((err) => {
-            onLogError(err, runId, "failed to record child process metadata");
-          });
-        }
+        const spawnPersistPromise =
+          typeof child.pid === "number" && child.pid > 0 && opts.onSpawn
+            ? opts.onSpawn({ pid: child.pid, startedAt }).catch((err) => {
+              onLogError(err, runId, "failed to record child process metadata");
+            })
+            : Promise.resolve();
 
         runningProcesses.set(runId, { child, graceSec: opts.graceSec });
 
@@ -1116,6 +1112,15 @@ export async function runChildProcess(
             .catch((err) => onLogError(err, runId, "failed to append stderr log chunk"));
         });
 
+        const stdin = child.stdin;
+        if (opts.stdin != null && stdin) {
+          void spawnPersistPromise.finally(() => {
+            if (child.killed || stdin.destroyed) return;
+            stdin.write(opts.stdin as string);
+            stdin.end();
+          });
+        }
+
         child.on("error", (err: Error) => {
           if (timeout) clearTimeout(timeout);
           runningProcesses.delete(runId);