diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6468112b..b4201dc2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -101,14 +101,22 @@ jobs:
           node-version: '22.19.0'
           cache: 'npm'
       - run: npm ci
-      - run: npm install --no-save --save-prod --legacy-peer-deps ai@7 @ai-sdk/openai@4 @ai-sdk/anthropic@4 ollama-ai-provider-v2@4 zod@4
+      # isolated-vm (optional peer, installed here only) rides the same install so it cannot be
+      # reverted by a later one. Pinned to 6.2.0: 7.x requires Node >= 24 and this job runs 22.19.0.
+      - run: npm install --no-save --save-prod --legacy-peer-deps ai@7 @ai-sdk/openai@4 @ai-sdk/anthropic@4 ollama-ai-provider-v2@4 zod@4 isolated-vm@6.2.0
       - run: npx tsc --noEmit
       - run: npm run test:types
       - run: npm run build
         env:
           NODE_OPTIONS: --max-old-space-size=12288
       - run: npm run build --workspace=packages/create-lousho-agent
+      # Runs the real 'isolate' driver (src/sandbox/isolate.test.ts): Node >= 20 needs
+      # --no-node-snapshot to load isolated-vm; LOUSHO_ISOLATE_TESTS=1 makes that file fail
+      # instead of skip if the module cannot load.
       - run: npx vitest run
+        env:
+          NODE_OPTIONS: --no-node-snapshot
+          LOUSHO_ISOLATE_TESTS: '1'
       - run: docker pull curlimages/curl:8.10.1 && docker pull node:20-alpine && docker pull node:22-slim
       - run: npm run test:docker
         env:
diff --git a/src/sandbox/isolate.test.ts b/src/sandbox/isolate.test.ts
index 64ecd9c7..fdf9ade2 100644
--- a/src/sandbox/isolate.test.ts
+++ b/src/sandbox/isolate.test.ts
@@ -1,11 +1,13 @@
 /**
  * The 'isolate' driver against an injected `isolated-vm` module, so the
  * timeout/OOM/driver mapping and the memory/timeout forwarding are tested
- * without the native package.
+ * without the native package. The last block runs the real driver against the
+ * native package (compat CI only; see probeIsolatedVm below).
  */
+import { createRequire } from 'node:module';
 import { describe, it, expect } from 'vitest';
-import { createIsolateDriver, ISOLATE_DEFAULTS } from './isolate';
-import { SandboxError } from './errors';
+import { createIsolateDriver, isolateDriver, ISOLATE_DEFAULTS } from './isolate';
+import { SandboxError, sandboxErrorKind } from './errors';
 
 type EvalCall = { code: string; args: unknown[]; options?: { arguments?: { copy?: boolean }; result?: { copy?: boolean; promise?: boolean }; timeout?: number } };
 
@@ -125,6 +127,17 @@ describe('createIsolateDriver', () => {
     await expect(driver.run('() => 1')).rejects.toMatchObject({ kind: 'driver', driver: 'isolate' });
   });
 
+  it("maps isolated-vm's own eval timeout (isolate still alive) to a timeout SandboxError", async () => {
+    const { module } = fakeModule({
+      eval: () => {
+        throw new Error('Script execution timed out.');
+      },
+    });
+    const driver = createIsolateDriver(module, LIMITS);
+
+    await expect(driver.run('() => 1')).rejects.toMatchObject({ kind: 'timeout', driver: 'isolate' });
+  });
+
   it("passes the code's own error through unchanged", async () => {
     const { module } = fakeModule();
     const driver = createIsolateDriver(module, LIMITS);
@@ -138,3 +151,66 @@ describe('ISOLATE_DEFAULTS', () => {
     expect(ISOLATE_DEFAULTS).toEqual({ memoryMb: 128, timeoutMs: 5_000 });
   });
 });
+
+/**
+ * The real driver, against the native `isolated-vm` package. Only the `compat`
+ * CI job installs it (`npm install --no-save isolated-vm`) and runs the suite
+ * with `NODE_OPTIONS=--no-node-snapshot` (isolated-vm on Node >= 20 crashes
+ * the process without that flag, so a loadable module alone is not enough).
+ * Everywhere else the block skips; under `LOUSHO_ISOLATE_TESTS=1` (compat)
+ * a missing module or flag fails instead, so CI cannot pass by skipping.
+ */
+function probeIsolatedVm(): { ok: boolean; reason: string } {
+  const needsFlag = Number(process.versions.node.split('.')[0]) >= 20;
+  const hasFlag = `${process.env.NODE_OPTIONS ?? ''} ${process.execArgv.join(' ')}`.includes('--no-node-snapshot');
+  if (needsFlag && !hasFlag) return { ok: false, reason: 'Node >= 20 needs --no-node-snapshot (NODE_OPTIONS) to load isolated-vm' };
+  try {
+    createRequire(import.meta.url)('isolated-vm');
+    return { ok: true, reason: '' };
+  } catch (error) {
+    return { ok: false, reason: `isolated-vm is not loadable: ${error instanceof Error ? error.message : String(error)}` };
+  }
+}
+
+const probe = probeIsolatedVm();
+/** True when the native isolated-vm loads in this process (so the real-driver block runs). */
+const hasIsolatedVm = probe.ok;
+const isolateRequired = process.env.LOUSHO_ISOLATE_TESTS === '1';
+
+if (isolateRequired && !hasIsolatedVm) {
+  describe('isolate driver (real isolated-vm)', () => {
+    it('is available when LOUSHO_ISOLATE_TESTS=1', () => {
+      throw new Error(`LOUSHO_ISOLATE_TESTS=1 is set but the real isolate driver cannot run: ${probe.reason}`);
+    });
+  });
+}
+
+describe.runIf(hasIsolatedVm)('isolate driver (real isolated-vm)', () => {
+  it('runs a real tool body and returns its value', async () => {
+    const driver = isolateDriver({ memoryMb: 128, timeoutMs: 5_000 });
+    await expect(driver.run('(a, b) => a + b', { args: [2, 40] })).resolves.toBe(42);
+    await expect(driver.run('async (n) => { await null; return { doubled: n * 2 }; }', { args: [21] })).resolves.toEqual({ doubled: 42 });
+  });
+
+  it("passes the code's own error through unchanged", async () => {
+    const driver = isolateDriver({ memoryMb: 128, timeoutMs: 5_000 });
+    const error = await driver.run('() => { throw new RangeError("boom") }').catch((e: unknown) => e);
+    expect(sandboxErrorKind(error)).toBeUndefined();
+    expect((error as Error).message).toContain('boom');
+  });
+
+  it('reports a timeout for a synchronous infinite loop', async () => {
+    const driver = isolateDriver({ memoryMb: 128, timeoutMs: 100 });
+    const error = await driver.run('() => { while (true) {} }').catch((e: unknown) => e);
+    expect(error).toBeInstanceOf(SandboxError);
+    expect(sandboxErrorKind(error)).toBe('timeout');
+  }, 15_000);
+
+  it('reports oom for a 256 MB allocation under a 32 MB cap', async () => {
+    const driver = isolateDriver({ memoryMb: 32, timeoutMs: 10_000 });
+    const error = await driver
+      .run('() => { const keep = []; for (let i = 0; i < 256; i++) keep.push(new Array(1024 * 1024 / 8).fill(i)); return keep.length; }')
+      .catch((e: unknown) => e);
+    expect(sandboxErrorKind(error)).toBe('oom');
+  }, 30_000);
+});
diff --git a/src/sandbox/isolate.ts b/src/sandbox/isolate.ts
index 73e3d1da..beefa8d6 100644
--- a/src/sandbox/isolate.ts
+++ b/src/sandbox/isolate.ts
@@ -76,6 +76,28 @@ if (typeof fn !== 'function') {
 return fn.apply(undefined, $1);
 `;
 
+/**
+ * What a failed run becomes: our own timer's kill or isolated-vm's eval timeout
+ * is 'timeout'; an isolate the engine disposed is 'oom' (the memory cap is the
+ * only configured limit, so a dead isolate means an OOM or a crash we report
+ * the same way); anything else is the code's own error, crossing unchanged.
+ */
+function classifyFailure(error: unknown, timedOut: boolean, disposed: boolean, limits: IsolateLimits): Error {
+  const engineTimeout = error instanceof Error && /Script execution timed out/i.test(error.message);
+  if (timedOut || engineTimeout) {
+    return new SandboxError(`the sandboxed run exceeded timeoutMs (${limits.timeoutMs} ms)`, 'timeout', DRIVER, { cause: error });
+  }
+  if (disposed) {
+    return new SandboxError(
+      `the sandboxed run exceeded the isolate's memory limit (memoryMb ${limits.memoryMb}) or crashed it`,
+      'oom',
+      DRIVER,
+      { cause: error }
+    );
+  }
+  return error instanceof Error ? error : new Error(typeof error === 'string' ? error : String(error));
+}
+
 async function runIsolated(module: IvmModule, limits: IsolateLimits, code: string, opts?: SandboxCallOptions): Promise<unknown> {
   let isolate: ivm.Isolate;
   try {
@@ -113,22 +135,7 @@ async function runIsolated(module: IvmModule, limits: IsolateLimits, code: strin
       stopped,
     ]);
   } catch (error) {
-    // Our timer disposed the isolate: the run outlasted timeoutMs.
-    if (timedOut) {
-      throw new SandboxError(`the sandboxed run exceeded timeoutMs (${limits.timeoutMs} ms)`, 'timeout', DRIVER, { cause: error });
-    }
-    // The engine disposed it otherwise: the memory cap is the only configured
-    // limit, so a dead isolate means an OOM (or a crash we report the same way).
-    if (isolate.isDisposed) {
-      throw new SandboxError(
-        `the sandboxed run exceeded the isolate's memory limit (memoryMb ${limits.memoryMb}) or crashed it`,
-        'oom',
-        DRIVER,
-        { cause: error }
-      );
-    }
-    // The code's own error crosses unchanged (it is not a boundary failure).
-    throw error instanceof Error ? error : new Error(typeof error === 'string' ? error : String(error));
+    throw classifyFailure(error, timedOut, isolate.isDisposed, limits);
   } finally {
     clearTimeout(timer);
     if (!isolate.isDisposed) {