diff --git a/src/process/supervisor/service-child-relay-host.test.ts b/src/process/supervisor/service-child-relay-host.test.ts
index 02057e5b13d0..31fc527fe649 100644
--- a/src/process/supervisor/service-child-relay-host.test.ts
+++ b/src/process/supervisor/service-child-relay-host.test.ts
@@ -466,11 +466,15 @@ it.each(["EPERM", "EIO", "still present"])(
   "keeps graceful cleanup uncertain when the kernel group is %s",
   async (failure) => {
     const { adapter, completeRoot, emit, close, groupProbe } = await createRelay("linux");
+    const cause =
+      failure === "still present"
+        ? undefined
+        : Object.assign(new Error(`synthetic ${failure}`), { code: failure });
     groupProbe.mockImplementation(() => {
-      if (failure === "still present") {
-        return true;
+      if (cause) {
+        throw cause;
       }
-      throw Object.assign(new Error(`synthetic ${failure}`), { code: failure });
+      return true;
     });
     completeRoot();
     await expect(adapter.wait()).resolves.toEqual({ code: 0, signal: null });
@@ -480,6 +484,9 @@ it.each(["EPERM", "EIO", "still present"])(
     vi.spyOn(Date, "now").mockReturnValueOnce(10_000).mockReturnValue(15_000);
     close();
     await expect(adapter.waitForExtinction()).rejects.toThrow("owned process group");
+    await expect(adapter.waitForExtinction()).rejects.toSatisfy(
+      (error: unknown) => error instanceof Error && error.cause === cause,
+    );
     await expect(adapter.wait()).resolves.toEqual({ code: 0, signal: null });
     expect(groupProbe).toHaveBeenCalledWith(-1235, 0);
     expect(groupProbe.mock.calls.every(([, signal]) => signal === 0)).toBe(true);
diff --git a/src/process/supervisor/service-child-relay-host.ts b/src/process/supervisor/service-child-relay-host.ts
index 3534a500afc3..334fe198c87c 100644
--- a/src/process/supervisor/service-child-relay-host.ts
+++ b/src/process/supervisor/service-child-relay-host.ts
@@ -255,12 +255,12 @@ export async function createServiceChildRelayAdapter(
   child.stderr?.once("end", settleWait);
   child.stderr?.once("close", settleWait);
 
-  const loseIdentity = (message: string) => {
+  const loseIdentity = (message: string, options?: ErrorOptions) => {
     if (state === "closed" || state === "identity-lost") {
       return;
     }
     state = "identity-lost";
-    waitError = new Error(`service child cleanup identity lost: ${message}`);
+    waitError = new Error(`service child cleanup identity lost: ${message}`, options);
     events.emitError(waitError, "process");
     if (!commandPid) {
       startup.reject(waitError);
@@ -347,12 +347,12 @@ export async function createServiceChildRelayAdapter(
       try {
         // Observation only: signalling a retired numeric PGID could hit a reused group.
         process.kill(-anchorPid, 0);
-      } catch (error) {
+      } catch (cause) {
         // SAFETY: process.kill throws Node system errors; only the exact ESRCH code certifies absence.
-        if ((error as NodeJS.ErrnoException).code === "ESRCH") {
+        if ((cause as NodeJS.ErrnoException).code === "ESRCH") {
           finishAuthorityClose(missingReceiptError);
         } else {
-          loseIdentity("owned process group disappearance could not be confirmed");
+          loseIdentity("owned process group disappearance could not be confirmed", { cause });
         }
         return;
       }