diff --git a/scripts/tsdown-build.mjs b/scripts/tsdown-build.mjs
index f51e085e04d..11edfa01a4c 100644
--- a/scripts/tsdown-build.mjs
+++ b/scripts/tsdown-build.mjs
@@ -32,6 +32,8 @@ const CGROUP_MEMORY_LIMIT_PATHS = [
 ];
 const PROC_MEMINFO_PATH = "/proc/meminfo";
 const TERMINATION_GRACE_MS = 5_000;
+const PROCESS_GROUP_EXIT_POLL_MS = 25;
+const POST_FORCE_KILL_WAIT_MS = 1_000;
 const ROOT_TSDOWN_OUTPUT_ROOTS = ["dist", "dist-runtime"];
 const PRESERVED_TSDOWN_OUTPUT_FILES = ["dist/cli-startup-metadata.json"];
 const PRESERVE_CLI_STARTUP_METADATA_ENV = "OPENCLAW_PRESERVE_CLI_STARTUP_METADATA";
@@ -607,13 +609,65 @@ export async function runTsdownBuildInvocation(invocation, params = {}) {
   let settled = false;
   let lastOutputAt = Date.now();
 
-  const child = spawn(invocation.command, invocation.args, invocation.options);
+  const useProcessGroup = timeoutMs !== null && process.platform !== "win32";
+  const child = spawn(invocation.command, invocation.args, {
+    ...invocation.options,
+    detached: useProcessGroup,
+  });
   const pidText = child.pid ? ` pid=${child.pid}` : "";
 
   function markOutput() {
     lastOutputAt = Date.now();
   }
 
+  function signalChild(signal) {
+    if (useProcessGroup && child.pid) {
+      try {
+        process.kill(-child.pid, signal);
+        return;
+      } catch {
+        // The group may already be gone; fall back to the direct child handle.
+      }
+    }
+    child.kill(signal);
+  }
+
+  function processTreeAlive() {
+    if (!child.pid) {
+      return false;
+    }
+    if (!useProcessGroup) {
+      return child.exitCode === null && child.signalCode === null;
+    }
+    try {
+      process.kill(-child.pid, 0);
+      return true;
+    } catch (error) {
+      return error?.code === "EPERM";
+    }
+  }
+
+  async function waitForProcessTreeExit(timeoutMsToWait) {
+    const deadlineAt = Date.now() + timeoutMsToWait;
+    while (Date.now() < deadlineAt) {
+      if (!processTreeAlive()) {
+        return true;
+      }
+      await new Promise((resolvePoll) => {
+        setTimeout(resolvePoll, PROCESS_GROUP_EXIT_POLL_MS);
+      });
+    }
+    return !processTreeAlive();
+  }
+
+  async function finishTimedOutProcessTree() {
+    if (!processTreeAlive()) {
+      return;
+    }
+    signalChild("SIGKILL");
+    await waitForProcessTreeExit(POST_FORCE_KILL_WAIT_MS);
+  }
+
   child.stdout?.on("data", (chunk) => {
     markOutput();
     scanner.append(chunk);
@@ -649,11 +703,11 @@ export async function runTsdownBuildInvocation(invocation, params = {}) {
       ? setTimeout(() => {
           timedOut = true;
           stderr.write(`[tsdown-build] timeout after ${timeoutMs}ms${pidText}; sending SIGTERM\n`);
-          child.kill("SIGTERM");
+          signalChild("SIGTERM");
           setTimeout(() => {
             if (!settled) {
               stderr.write(`[tsdown-build] forcing SIGKILL${pidText}\n`);
-              child.kill("SIGKILL");
+              signalChild("SIGKILL");
             }
           }, TERMINATION_GRACE_MS).unref();
         }, timeoutMs).unref()
@@ -674,16 +728,25 @@ export async function runTsdownBuildInvocation(invocation, params = {}) {
       });
     });
     child.once("close", (status, signal) => {
-      settled = true;
-      clearInterval(heartbeat);
-      clearTimeout(timeout);
-      resolve({
-        status,
-        signal,
-        timedOut,
-        error: null,
-        ...scanner.finish(),
-      });
+      function finish() {
+        settled = true;
+        clearInterval(heartbeat);
+        clearTimeout(timeout);
+        resolve({
+          status,
+          signal,
+          timedOut,
+          error: null,
+          ...scanner.finish(),
+        });
+      }
+
+      if (timedOut) {
+        void finishTimedOutProcessTree().then(finish, finish);
+        return;
+      }
+
+      finish();
     });
   });
 }
diff --git a/test/scripts/tsdown-build.test.ts b/test/scripts/tsdown-build.test.ts
index 65058ee0412..26915f5106e 100644
--- a/test/scripts/tsdown-build.test.ts
+++ b/test/scripts/tsdown-build.test.ts
@@ -37,6 +37,41 @@ async function expectPathMissing(targetPath: string) {
   expect(Reflect.get(statError, "code")).toBe("ENOENT");
 }
 
+function isProcessAlive(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(filePath: string, timeoutMs: number): Promise<void> {
+  const deadlineAt = Date.now() + timeoutMs;
+  while (Date.now() < deadlineAt) {
+    if (fs.existsSync(filePath)) {
+      return;
+    }
+    await sleep(25);
+  }
+  throw new Error(`timed out waiting for ${filePath}`);
+}
+
+async function waitForDead(pid: number, timeoutMs: number): Promise<void> {
+  const deadlineAt = Date.now() + timeoutMs;
+  while (Date.now() < deadlineAt) {
+    if (!isProcessAlive(pid)) {
+      return;
+    }
+    await sleep(25);
+  }
+  throw new Error(`timed out waiting for pid ${pid} to exit`);
+}
+
 describe("resolveTsdownBuildInvocation", () => {
   it("parses wrapper help before any tsdown work", () => {
     expect(parseTsdownBuildArgs(["--help"])).toEqual({ forwardedArgs: [], help: true });
@@ -610,4 +645,58 @@ describe("runTsdownBuildInvocation", () => {
     expect(result.signal).toBe("SIGTERM");
     expect(output.chunks.join("")).toContain("timeout after 50ms");
   });
+
+  it.skipIf(process.platform === "win32")(
+    "kills timed-out tsdown process groups when the wrapper exits first",
+    async () => {
+      const rootDir = createTempDir("openclaw-tsdown-timeout-");
+      const childPidPath = path.join(rootDir, "child.pid");
+      let childPid = 0;
+      const childScript = "process.on('SIGTERM', () => {}); setInterval(() => {}, 1000);";
+      const parentScript = [
+        "const { spawn } = require('node:child_process');",
+        "const fs = require('node:fs');",
+        `const child = spawn(process.execPath, ['-e', ${JSON.stringify(childScript)}], { stdio: 'ignore' });`,
+        `fs.writeFileSync(${JSON.stringify(childPidPath)}, String(child.pid));`,
+        "process.on('SIGTERM', () => process.exit(0));",
+        "setInterval(() => {}, 1000);",
+      ].join("");
+
+      try {
+        const output = createWriteSink();
+        const runPromise = runTsdownBuildInvocation(
+          {
+            command: process.execPath,
+            args: ["-e", parentScript],
+            options: {
+              stdio: ["ignore", "pipe", "pipe"],
+              shell: false,
+              env: process.env,
+            },
+          },
+          {
+            stdout: output.sink,
+            stderr: output.sink,
+            env: {
+              ...process.env,
+              OPENCLAW_TSDOWN_HEARTBEAT_MS: "0",
+              OPENCLAW_TSDOWN_TIMEOUT_MS: "50",
+            },
+          },
+        );
+
+        await waitForFile(childPidPath, 2_000);
+        childPid = Number.parseInt(fs.readFileSync(childPidPath, "utf8"), 10);
+        expect(isProcessAlive(childPid)).toBe(true);
+        const result = await runPromise;
+
+        expect(result.timedOut).toBe(true);
+        await waitForDead(childPid, 2_000);
+      } finally {
+        if (childPid && isProcessAlive(childPid)) {
+          process.kill(childPid, "SIGKILL");
+        }
+      }
+    },
+  );
 });