feat(runtime): stage VM runtime artifacts and writable drives in per-VM ephemeral storage by default

test/test.ts

@@ -678,6 +678,84 @@ tap.test('MicroVM - invalid lifecycle calls should throw SmartVMError', async ()
   expect((infoError as SmartVMError).code).toEqual('NO_CLIENT');
 });
 
+tap.test('MicroVM - start() should stage writable drives ephemerally and clean them up on failure', async () => {
+  const workDir = await fs.promises.mkdtemp(path.join(os.tmpdir(), 'smartvm-ephemeral-drive-test-'));
+  const runtimeDir = path.join(workDir, 'runtime');
+  const sourceRootfs = path.join(workDir, 'rootfs.ext4');
+  await fs.promises.writeFile(sourceRootfs, 'persistent-rootfs');
+
+  const config: IMicroVMConfig = {
+    ...sampleConfig,
+    id: 'ephemeral-vm',
+    drives: [
+      {
+        driveId: 'rootfs',
+        pathOnHost: sourceRootfs,
+        isRootDevice: true,
+        isReadOnly: false,
+      },
+    ],
+    networkInterfaces: [],
+  };
+  const vm = new MicroVM(
+    'ephemeral-vm',
+    config,
+    '/bin/false',
+    path.join(runtimeDir, 'ephemeral-vm', 'firecracker.sock'),
+    new NetworkManager(),
+    { runtimeDir },
+  );
+
+  try {
+    const error = await getRejectedError(vm.start());
+    expect(error).toBeInstanceOf(SmartVMError);
+    expect(fs.existsSync(path.join(runtimeDir, 'ephemeral-vm'))).toBeFalse();
+    expect(await fs.promises.readFile(sourceRootfs, 'utf8')).toEqual('persistent-rootfs');
+    expect(vm.getVMConfig().config.drives![0].pathOnHost).not.toEqual(sourceRootfs);
+  } finally {
+    await fs.promises.rm(workDir, { recursive: true, force: true });
+  }
+});
+
+tap.test('MicroVM - start() should honor per-drive ephemeral opt-out', async () => {
+  const workDir = await fs.promises.mkdtemp(path.join(os.tmpdir(), 'smartvm-persistent-drive-test-'));
+  const runtimeDir = path.join(workDir, 'runtime');
+  const sourceRootfs = path.join(workDir, 'rootfs.ext4');
+  await fs.promises.writeFile(sourceRootfs, 'persistent-rootfs');
+
+  const config: IMicroVMConfig = {
+    ...sampleConfig,
+    id: 'persistent-vm',
+    drives: [
+      {
+        driveId: 'rootfs',
+        pathOnHost: sourceRootfs,
+        isRootDevice: true,
+        isReadOnly: false,
+        ephemeral: false,
+      },
+    ],
+    networkInterfaces: [],
+  };
+  const vm = new MicroVM(
+    'persistent-vm',
+    config,
+    '/bin/false',
+    path.join(runtimeDir, 'persistent-vm', 'firecracker.sock'),
+    new NetworkManager(),
+    { runtimeDir },
+  );
+
+  try {
+    const error = await getRejectedError(vm.start());
+    expect(error).toBeInstanceOf(SmartVMError);
+    expect(vm.getVMConfig().config.drives![0].pathOnHost).toEqual(sourceRootfs);
+    expect(fs.existsSync(path.join(runtimeDir, 'persistent-vm'))).toBeFalse();
+  } finally {
+    await fs.promises.rm(workDir, { recursive: true, force: true });
+  }
+});
+
 // ============================================================
 // SmartVM Tests
 // ============================================================
@@ -688,6 +766,9 @@ tap.test('SmartVM - instantiation with defaults', async () => {
   expect(smartvm.imageManager).toBeTruthy();
   expect(smartvm.baseImageManager).toBeTruthy();
   expect(smartvm.networkManager).toBeTruthy();
+  if (fs.existsSync('/dev/shm')) {
+    expect(smartvm.getRuntimeDir()).toEqual('/dev/shm/.smartvm/runtime');
+  }
   expect(smartvm.vmCount).toEqual(0);
   expect(smartvm.listVMs()).toHaveLength(0);
 });