From 03a9e022ed83f8d6c4e7b1f417a9d7919b6fc3da Mon Sep 17 00:00:00 2001
From: Peter Steinberger <steipete@gmail.com>
Date: Wed, 5 Aug 2026 06:57:55 -0700
Subject: [PATCH] fix(managed-child): honor process groups that vanish before
 cleanup (#119614)

---
 scripts/lib/managed-child-process.mjs      | 24 +++++----------
 test/scripts/managed-child-process.test.ts | 34 ++++++++++++++++++++++
 2 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/scripts/lib/managed-child-process.mjs b/scripts/lib/managed-child-process.mjs
index b6f6aa3e6061..4cf35f027778 100644
--- a/scripts/lib/managed-child-process.mjs
+++ b/scripts/lib/managed-child-process.mjs
@@ -144,7 +144,6 @@ export async function runManagedCommand({
   let timeoutTimer = null;
   let signalTimeout;
   let timedOut = false;
-  let childResult;
   let timeoutTermination;
   const timeoutTriggered = new Promise((resolve) => {
     signalTimeout = resolve;
@@ -222,14 +221,10 @@ export async function runManagedCommand({
       }
       throw outcome.error;
     }
-    childResult = outcome.status;
     if (requireProcessTreeExit) {
-      await ensureManagedProcessTreeExit(child, platform, {
-        rejectIfLive: true,
-        terminateIfLive: true,
-      });
+      await ensureManagedProcessTreeExit(child, platform, { terminateIfLive: true });
     }
-    return childResult;
+    return outcome.status;
   } finally {
     if (timeoutTimer) {
       clearTimeout(timeoutTimer);
@@ -276,7 +271,7 @@ function processGroupStatus(pid) {
 async function ensureManagedProcessTreeExit(
   child,
   platform,
-  { rejectIfLive = false, terminateIfLive = false, windowsTermination } = {},
+  { terminateIfLive = false, windowsTermination } = {},
 ) {
   if (platform === "win32") {
     if (windowsTermination?.processTreeState === "indeterminate") {
@@ -294,10 +289,10 @@ async function ensureManagedProcessTreeExit(
     return;
   }
   let status = initialStatus;
-  let sawLive = initialStatus === "live";
-  if (terminateIfLive) {
-    terminateManagedChild(child, "SIGKILL", { platform });
-  }
+  // A missing group at signal time supersedes the earlier racy liveness probe.
+  const termination = terminateIfLive
+    ? terminateManagedChild(child, "SIGKILL", { platform })
+    : undefined;
   const deadline = Date.now() + PROCESS_GROUP_DRAIN_TIMEOUT_MS;
   while (Date.now() < deadline) {
     await new Promise((resolve) => {
@@ -305,7 +300,7 @@ async function ensureManagedProcessTreeExit(
     });
     status = processGroupStatus(child.pid);
     if (status === "dead") {
-      if (rejectIfLive && sawLive) {
+      if (terminateIfLive && termination?.processTreeState !== "terminated") {
         throw createManagedCommandCleanupError(
           "Managed command exited while its process group remained active",
           child,
@@ -315,9 +310,6 @@ async function ensureManagedProcessTreeExit(
       }
       return;
     }
-    if (status === "live") {
-      sawLive = true;
-    }
   }
   const processTreeState = status === "indeterminate" ? "indeterminate" : "live";
   throw createManagedCommandCleanupError(
diff --git a/test/scripts/managed-child-process.test.ts b/test/scripts/managed-child-process.test.ts
index 81f6528b2945..46bd3b59151a 100644
--- a/test/scripts/managed-child-process.test.ts
+++ b/test/scripts/managed-child-process.test.ts
@@ -418,6 +418,40 @@ setInterval(() => {}, 1_000);
     expect(isProcessAlive(childPid)).toBe(false);
   });
 
+  posixIt("accepts a process group that vanishes before its cleanup signal", async () => {
+    const originalKill = process.kill;
+    let childPid = 0;
+    let injectedLiveGroup = false;
+    process.kill = ((pid: number, signal?: NodeJS.Signals | number) => {
+      if (pid === -childPid && signal === 0 && !injectedLiveGroup) {
+        injectedLiveGroup = true;
+        return true;
+      }
+      return originalKill(pid, signal);
+    }) as typeof process.kill;
+
+    try {
+      await expect(
+        runManagedCommand({
+          bin: process.execPath,
+          args: ["-e", "process.exit(0)"],
+          onReady: (child) => {
+            childPid = expectProcessPid(child.pid);
+          },
+          requireProcessTreeExit: true,
+          shell: false,
+          stdio: "ignore",
+          timeoutMs: 1_000,
+        }),
+      ).resolves.toBe(0);
+    } finally {
+      process.kill = originalKill;
+    }
+
+    expect(injectedLiveGroup).toBe(true);
+    expect(isProcessAlive(childPid)).toBe(false);
+  });
+
   it("allows bounded retry output and normal long-running work to complete", async () => {
     await expect(
       runManagedCommand({