diff --git a/test/e2e/qa-lab/plugins/plugin-lifecycle-probe-runtime.ts b/test/e2e/qa-lab/plugins/plugin-lifecycle-probe-runtime.ts
index 7adb3cbc4979..6cb934436449 100644
--- a/test/e2e/qa-lab/plugins/plugin-lifecycle-probe-runtime.ts
+++ b/test/e2e/qa-lab/plugins/plugin-lifecycle-probe-runtime.ts
@@ -234,13 +234,16 @@ async function runCommand(command: string, args: readonly string[], options: Com
   try {
     await new Promise<void>((resolve, reject) => {
       const spawnImpl = options.spawnImpl ?? spawn;
+      const useProcessGroup = process.platform !== "win32";
       const child = spawnImpl(command, args, {
         cwd: process.cwd(),
+        detached: useProcessGroup,
         env: options.env ?? process.env,
         stdio: outputFd === undefined ? "inherit" : (["ignore", outputFd, outputFd] as const),
       });
       let settled = false;
       let forceKillTimer: NodeJS.Timeout | undefined;
+      let forceSettleTimer: NodeJS.Timeout | undefined;
       let timeoutTimer: NodeJS.Timeout | undefined;
       let timeoutError: Error | undefined;
       const clearTimers = () => {
@@ -250,6 +253,43 @@ async function runCommand(command: string, args: readonly string[], options: Com
         if (forceKillTimer) {
           clearTimeout(forceKillTimer);
         }
+        if (forceSettleTimer) {
+          clearTimeout(forceSettleTimer);
+        }
+      };
+      const signalChild = (signal: NodeJS.Signals) => {
+        if (useProcessGroup && child.pid) {
+          try {
+            process.kill(-child.pid, signal);
+            return;
+          } catch {
+            // The process group may already be gone; fall back to the direct child.
+          }
+        }
+        child.kill(signal);
+      };
+      const isProcessGroupRunning = () => {
+        if (!useProcessGroup || !child.pid) {
+          return false;
+        }
+        try {
+          process.kill(-child.pid, 0);
+          return true;
+        } catch (error) {
+          return (error as NodeJS.ErrnoException).code === "EPERM";
+        }
+      };
+      const finish = (error?: Error) => {
+        if (settled) {
+          return;
+        }
+        settled = true;
+        clearTimers();
+        if (error) {
+          reject(error);
+          return;
+        }
+        resolve();
       };
       timeoutTimer =
         options.timeoutMs === undefined
@@ -258,37 +298,38 @@ async function runCommand(command: string, args: readonly string[], options: Com
               timeoutError = new Error(
                 `${command} ${args.join(" ")} timed out after ${options.timeoutMs}ms`,
               );
-              child.kill("SIGTERM");
-              forceKillTimer = setTimeout(
-                () => child.kill("SIGKILL"),
-                options.timeoutKillGraceMs ?? 2_000,
-              );
+              signalChild("SIGTERM");
+              forceKillTimer = setTimeout(() => {
+                forceKillTimer = undefined;
+                signalChild("SIGKILL");
+                forceSettleTimer = setTimeout(
+                  () => finish(timeoutError),
+                  options.timeoutKillGraceMs ?? 2_000,
+                );
+                forceSettleTimer.unref();
+              }, options.timeoutKillGraceMs ?? 2_000);
               forceKillTimer.unref();
             }, options.timeoutMs);
       timeoutTimer?.unref();
       child.once("error", (error) => {
-        if (settled) {
-          return;
-        }
-        settled = true;
-        clearTimers();
-        reject(error);
+        finish(error);
       });
       child.once("exit", (code, signal) => {
         if (settled) {
           return;
         }
-        settled = true;
-        clearTimers();
         if (timeoutError) {
-          reject(timeoutError);
+          if (isProcessGroupRunning()) {
+            return;
+          }
+          finish(timeoutError);
           return;
         }
         if (code === 0 && !signal) {
-          resolve();
+          finish();
           return;
         }
-        reject(new Error(`${command} ${args.join(" ")} failed with ${signal ?? `exit ${code}`}`));
+        finish(new Error(`${command} ${args.join(" ")} failed with ${signal ?? `exit ${code}`}`));
       });
     });
   } catch (error) {
diff --git a/test/e2e/qa-lab/plugins/plugin-lifecycle-probe.e2e.test.ts b/test/e2e/qa-lab/plugins/plugin-lifecycle-probe.e2e.test.ts
index a353ccaa96b6..0aff24aafe79 100644
--- a/test/e2e/qa-lab/plugins/plugin-lifecycle-probe.e2e.test.ts
+++ b/test/e2e/qa-lab/plugins/plugin-lifecycle-probe.e2e.test.ts
@@ -1,6 +1,6 @@
 // Plugin Lifecycle Probe tests cover QA Lab plugin lifecycle evidence.
 import { EventEmitter } from "node:events";
-import { mkdirSync, writeFileSync } from "node:fs";
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
 import path from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import { createTempDirTracker } from "../../../helpers/temp-dir.js";
@@ -17,6 +17,32 @@ function makeTempDir(): string {
   return tempDirs.make("openclaw-plugin-lifecycle-probe-");
 }
 
+function isProcessRunning(pid: number): boolean {
+  try {
+    process.kill(pid, 0);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+async function sleep(ms: number): Promise<void> {
+  await new Promise((resolve) => {
+    setTimeout(resolve, ms);
+  });
+}
+
+async function waitForFile(pathToCheck: string, timeoutMs: number): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (existsSync(pathToCheck)) {
+      return;
+    }
+    await sleep(25);
+  }
+  throw new Error(`Timed out waiting for ${pathToCheck}`);
+}
+
 class FakeCommandChild extends EventEmitter {
   readonly signals: string[] = [];
 
@@ -109,4 +135,47 @@ describe("plugin lifecycle matrix probe", () => {
       vi.useRealTimers();
     }
   });
+
+  it("keeps fallback SIGKILL armed for ignored-stdio descendants", async () => {
+    if (process.platform === "win32") {
+      return;
+    }
+
+    const dir = makeTempDir();
+    const descendantPidPath = path.join(dir, "descendant.pid");
+    let descendantPid: number | undefined;
+    try {
+      const childScript = "process.on('SIGTERM', () => {}); setInterval(() => {}, 1000);";
+      const parentScript = [
+        "import { spawn } from 'node:child_process';",
+        "import { writeFileSync } from 'node:fs';",
+        `const child = spawn(process.execPath, ['-e', ${JSON.stringify(childScript)}], { stdio: 'ignore' });`,
+        "child.unref();",
+        "writeFileSync(process.env.OPENCLAW_TEST_DESCENDANT_PID, String(child.pid));",
+        "process.on('SIGTERM', () => process.exit(0));",
+        "setInterval(() => {}, 1000);",
+      ].join("\n");
+
+      const run = probeTesting.runCommand(
+        process.execPath,
+        ["--input-type=module", "-e", parentScript],
+        {
+          env: { ...process.env, OPENCLAW_TEST_DESCENDANT_PID: descendantPidPath },
+          timeoutKillGraceMs: 250,
+          timeoutMs: 500,
+        },
+      );
+      await waitForFile(descendantPidPath, 2_000);
+      await sleep(300);
+
+      await expect(run).rejects.toThrow(/timed out after 500ms/u);
+
+      descendantPid = Number(readFileSync(descendantPidPath, "utf8"));
+      expect(isProcessRunning(descendantPid)).toBe(false);
+    } finally {
+      if (descendantPid && isProcessRunning(descendantPid)) {
+        process.kill(descendantPid, "SIGKILL");
+      }
+    }
+  });
 });