diff --git a/src/process/DarwinProcessRunTokenReader.ts b/src/process/DarwinProcessRunTokenReader.ts
index f01d4fc2ae..fd2a50407f 100644
--- a/src/process/DarwinProcessRunTokenReader.ts
+++ b/src/process/DarwinProcessRunTokenReader.ts
@@ -523,6 +523,7 @@ export const createDarwinProcessRunTokenReader = (
           maxBuffer: 1024 * 1024,
           signal,
           stopSignal: SWIFTC_INTERRUPT,
+          lifetimePipe: true,
           env: compilerEnvironment,
         });
       } catch (cause: unknown) {
@@ -535,9 +536,9 @@ export const createDarwinProcessRunTokenReader = (
     } catch (cause: unknown) {
       operation.primaryFailure = { cause };
       if (operationRoot !== undefined) {
-        // execFileOutput has settled, so inherited compiler pipes are closed.
-        // That is not proof for a child that did not inherit them; this owner
-        // does not signal processes it did not launch.
+        // The extra pipe keeps settlement pending for Swift frontend writers
+        // that inherit it after the driver and its standard streams close.
+        // It cannot establish completion of a child that did not inherit it.
         try {
           await cleanupRoot(operationRoot);
         } catch (cleanup: unknown) {
diff --git a/src/process/ExecFileOutput.test.ts b/src/process/ExecFileOutput.test.ts
index 14cc0f59b4..60066cb19a 100644
--- a/src/process/ExecFileOutput.test.ts
+++ b/src/process/ExecFileOutput.test.ts
@@ -68,6 +68,14 @@ it.each([undefined, "SIGTERM"] as const)(
   },
 );
 
+it("rejects a lifetime pipe without a stoppable command", async () => {
+  await expect(
+    execFileOutput(process.execPath, ["-e", "process.exit(0)"], {
+      lifetimePipe: true,
+    }),
+  ).rejects.toThrow("lifetimePipe requires stopSignal");
+});
+
 describe("execFileOutput", () => {
   it("ignores non-Error and incomplete failure metadata", () => {
     expect(execFileOutputFailure("failure")).toBeUndefined();
diff --git a/src/process/ExecFileOutput.ts b/src/process/ExecFileOutput.ts
index 86f3920391..19522a6901 100644
--- a/src/process/ExecFileOutput.ts
+++ b/src/process/ExecFileOutput.ts
@@ -20,6 +20,8 @@ type ExecFileOutputOptions = Omit<
    * execFile sends SIGTERM on abort and rejects before the process exits.
    */
   readonly stopSignal?: NodeJS.Signals;
+  /** Wait for inherited copies of an extra drained descriptor to close. Requires stopSignal. */
+  readonly lifetimePipe?: boolean;
 };
 
 /** How long a stopped process may take to exit before it is killed. */
@@ -149,7 +151,12 @@ export const execFileBytes = (
   options: ExecFileOutputOptions = {},
 ): Promise<{ readonly stdout: Buffer; readonly stderr: Buffer }> =>
   new Promise((resolve, reject) => {
-    const { stopSignal, signal, timeout, ...execOptions } = options;
+    const { stopSignal, signal, timeout, lifetimePipe, ...execOptions } =
+      options;
+    if (lifetimePipe === true && stopSignal === undefined) {
+      reject(new TypeError("lifetimePipe requires stopSignal"));
+      return;
+    }
     const invalid = timeout === undefined ? undefined : invalidTimeout(timeout);
     if (invalid !== undefined) {
       reject(invalid);
@@ -213,7 +220,7 @@ const startStoppableCommand = (
   options: ExecFileOutputOptions & { readonly stopSignal: NodeJS.Signals },
   complete: (error: Error | null, stdout: Buffer, stderr: Buffer) => void,
 ): void => {
-  const { stopSignal, signal, timeout, ...execOptions } = options;
+  const { stopSignal, signal, timeout, lifetimePipe, ...execOptions } = options;
   const maxBuffer = options.maxBuffer ?? Number.POSITIVE_INFINITY;
   if (typeof maxBuffer !== "number" || !(maxBuffer >= 0)) {
     const error = new RangeError("maxBuffer must be a nonnegative number");
@@ -231,9 +238,16 @@ const startStoppableCommand = (
   // pipe lifetime of descendants still using caller-owned temporary files.
   const child = spawn(command, [...arguments_], {
     ...execOptions,
-    stdio: ["ignore", "pipe", "pipe"],
+    stdio:
+      lifetimePipe === true
+        ? ["ignore", "pipe", "pipe", "pipe"]
+        : ["ignore", "pipe", "pipe"],
     killSignal: stopSignal,
   });
+  if (lifetimePipe === true) {
+    const pipe = child.stdio[3];
+    if (pipe != null && "resume" in pipe) pipe.resume();
+  }
   // The first stop request names the failure; a later one is not resent.
   const stop = (reason: "abort" | "timeout" | "output-limit"): void => {
     if (stopped !== undefined || rootFailed || processError !== null) return;
@@ -244,7 +258,10 @@ const startStoppableCommand = (
   const onAbort = (): void => {
     stop("abort");
   };
-  const capture = (stream: typeof child.stdout, name: "stdout" | "stderr") => {
+  const capture = (
+    stream: NonNullable<typeof child.stdout>,
+    name: "stdout" | "stderr",
+  ) => {
     const chunks: Buffer[] = [];
     let retained = 0;
     stream.on("data", (chunk: Buffer) => {
@@ -266,8 +283,8 @@ const startStoppableCommand = (
     });
     return () => Buffer.concat(chunks, retained);
   };
-  const stdout = capture(child.stdout, "stdout");
-  const stderr = capture(child.stderr, "stderr");
+  const stdout = capture(child.stdout!, "stdout");
+  const stderr = capture(child.stderr!, "stderr");
   child.on("error", (error: Error) => {
     processError ??= error;
   });
diff --git a/tests/boundary/process/darwinProcessRunTokenReader.test.ts b/tests/boundary/process/darwinProcessRunTokenReader.test.ts
index f3c5ccbd97..64d224a3b0 100644
--- a/tests/boundary/process/darwinProcessRunTokenReader.test.ts
+++ b/tests/boundary/process/darwinProcessRunTokenReader.test.ts
@@ -813,9 +813,8 @@ const temporaryStateSchema = z.object({
 });
 
 /**
- * A compiler that behaves like swift-driver: a job in its own process group
- * writes an object under TMPDIR, SIGINT stops the job and deletes the object,
- * and any other signal leaves the job writing after the driver exits.
+ * A compiler whose detached job closes standard streams but retains fd 3,
+ * writes an object after the SIGINT-stopped driver exits, then closes fd 3.
  */
 const writeTemporaryObjectCompiler = async (directory: string) => {
   const executable = join(directory, "fake-temporary-xcrun");
@@ -828,14 +827,14 @@ const path = process.getBuiltinModule("node:path");
 const { spawn } = process.getBuiltinModule("node:child_process");
 const temporary = fs.mkdtempSync(path.join(os.tmpdir(), "TemporaryDirectory."));
 const object = path.join(temporary, "ProcessRunTokenReader-1.o");
+let lifetime = "ignore";
+try { if (fs.fstatSync(3).isSocket()) lifetime = 3; } catch {}
 const job = spawn(process.execPath, ["-e",
   "setTimeout(() => { const fs = process.getBuiltinModule('node:fs'); fs.mkdirSync(" + JSON.stringify(temporary) +
   ", { recursive: true }); fs.writeFileSync(" + JSON.stringify(object) + ", 'object'); }, 300)"],
-  { detached: true, stdio: "ignore" });
+  { detached: true, stdio: ["ignore", "ignore", "ignore", lifetime] });
 job.unref();
 process.on("SIGINT", () => {
-  job.kill("SIGKILL");
-  fs.rmSync(object, { force: true });
   process.exit(130);
 });
 const output = process.argv[process.argv.indexOf("-o") + 1];