diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..4ee7690
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,37 @@
+# Mirrors the root package.json scripts step for step: keep the two in
+# correspondence when adding a check to either side.
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  verify:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+
+      - run: npm ci
+
+      - run: npm run typecheck
+
+      - run: npm test
+
+      - run: npm run build
+
+      - name: Version lockstep
+        run: npm run check-version
diff --git a/README.md b/README.md
index d563660..66851a0 100644
--- a/README.md
+++ b/README.md
@@ -42,14 +42,31 @@ npm test
 npm run build
 ```
 
-Releases bump every package to one version, then publish them all:
+Releases bump every package to one version, then publish them all. `npm version`
+fans the bump out through `scripts/set-version.mjs` (workspace manifests, internal
+ranges, embedded `VERSION` constants) and refreshes the lockfile. It also creates
+a release commit and a `v<version>` tag, and refuses to run on a dirty tree, so
+commit or stash first. Pass `-m` to keep the `chore(release): vX.Y.Z` commit
+convention:
 
 ```sh
-npm run set-version -- 0.2.0
+npm version 0.2.0 -m 'chore(release): v%s'
 npm run build
 npm publish --workspaces
 ```
 
+Add `--no-git-tag-version` to skip the commit and tag; the bump is then left
+staged for you to commit yourself.
+
+To bump without `npm version`, run `npm run set-version -- 0.2.0` followed by
+`npm install --package-lock-only`; `check-version` does not inspect the lockfile,
+so a bare `set-version` leaves `package-lock.json` behind unnoticed.
+
+`npm run check-version` verifies the lockstep without changing anything:
+every manifest on the root version, every internal dependency range at
+`^<version>`, every embedded `VERSION` constant matching. CI runs it alongside
+typecheck, test, and build on every pull request and push to `main`.
+
 ## Getting started (operators)
 
 ```sh
diff --git a/okf-bundle/decisions/cdk-tests-share-one-outdir.md b/okf-bundle/decisions/cdk-tests-share-one-outdir.md
new file mode 100644
index 0000000..6b60af9
--- /dev/null
+++ b/okf-bundle/decisions/cdk-tests-share-one-outdir.md
@@ -0,0 +1,51 @@
+---
+type: decision
+title: CDK construct tests share one cloud-assembly outdir
+description: Why construct tests build their App with test/support/test-app.ts
+  instead of new App(), and why vitest's timeout is 30 s.
+tags:
+  - millwright
+  - testing
+  - cdk
+timestamp: 2026-09-08T03:23:12.874Z
+---
+
+Every `Template.fromStack(...)` over the `Millwright` construct synthesizes a full stack, and that
+stack bundles **ten `NodejsFunction` Lambdas with esbuild** (poller, launcher, sweep, three synth-job
+functions, two run-executor functions, reporter, step-events writer) plus the synth tooling bundle
+from `millwright-cli`. One synth costs roughly 1.5 s on a fast workstation and 5–11 s on a loaded
+GitHub Actions runner — past vitest's 5 s default per-test budget. That is what made the first CI
+workflow run (PR #36) fail with timeouts in `data-stores`, `millwright` and `run-executor-construct`.
+
+## What was decided
+
+- Construct tests build their App with `testApp()` from `packages/millwright-cdk/test/support/test-app.ts`,
+  never a bare `new App()`. The helper pins one cloud-assembly outdir per worker process.
+- The root `vitest.config.ts` sets `testTimeout: 30_000`.
+
+## Why the shared outdir works
+
+`aws-cdk-lib`'s `AssetStaging` keeps a **process-wide cache** keyed on (outdir, source path, bundling
+options). A bare `new App()` picks a fresh temp outdir every time, so the cache never hits and every
+test in a file re-runs all the esbuild bundles. With one outdir per process the first synth in a file
+bundles and every later synth reuses it: `data-stores.test.ts` dropped from ~21 s to ~4.5 s locally.
+
+The outdir must be **per process**, not shared across vitest workers: each App writes
+`manifest.json` and `Test.template.json` into it, and concurrent workers would race on those files.
+
+## Why not `CDK_OUTDIR`
+
+Setting the env var would reach every `new App()` without touching tests, but `App` treats a set
+`CDK_OUTDIR` as a request for `autoSynth`, registering a `beforeExit` listener per App. Hundreds of
+Apps per run means listener-leak warnings and exit-time synths of half-built trees from the
+"throws at construct time" tests.
+
+## Why not disable bundling
+
+The `aws:cdk:bundling-stacks` context can skip bundling entirely, but the tests would then stop
+exercising the real bundling configuration (workspace aliases, entry points, formats).
+
+## Citations
+
+[1] [test-app.ts](../../packages/millwright-cdk/test/support/test-app.ts)
+[2] [vitest.config.ts](../../vitest.config.ts)
diff --git a/okf-bundle/decisions/index.md b/okf-bundle/decisions/index.md
index 3e63f63..e9becbe 100644
--- a/okf-bundle/decisions/index.md
+++ b/okf-bundle/decisions/index.md
@@ -3,6 +3,7 @@
 # Concepts
 
 * [BatchGetBuilds is authoritative for terminal job state](batchgetbuilds-authoritative.md)
+* [CDK construct tests share one cloud-assembly outdir](cdk-tests-share-one-outdir.md) - Why construct tests build their App with test/support/test-app.ts instead of new App(), and why vitest's timeout is 30 s.
 * [Caught-timeout wake instead of task heartbeats](no-heartbeat-wake.md)
 * [Why polling instead of webhooks](no-webhooks.md)
 * [The poller is non-VPC](non-vpc-poller.md)
diff --git a/okf-bundle/interfaces/packages.md b/okf-bundle/interfaces/packages.md
index 9a47e89..3cf6f1f 100644
--- a/okf-bundle/interfaces/packages.md
+++ b/okf-bundle/interfaces/packages.md
@@ -30,11 +30,19 @@ between "millwright's own deployment is CDK" and "your workflows are not CDK".
 ```sh
 npm install && npm run typecheck && npm test && npm run build
 
-npm run set-version -- 0.2.0    # bump every package to one version
+npm version 0.2.0 -m 'chore(release): v%s'   # bump every package, commit, tag v0.2.0
 npm run build
 npm publish --workspaces
 ```
 
+`npm run check-version` (`scripts/set-version.mjs --check`) asserts the lockstep without writing:
+every manifest on the root version, every `@copperbox/millwright-*` range at `^<version>`, every
+`src/version.ts` `VERSION` matching. `.github/workflows/ci.yml` runs typecheck, test, build, and
+this check on pull requests and pushes to `main`. The root `version` lifecycle script fans an
+`npm version` bump through `set-version.mjs` and refreshes the lockfile. `npm version` then
+commits and tags `v<version>`, and it refuses to run on a dirty tree; `--no-git-tag-version`
+leaves the bump staged without a commit or tag. Publishing stays manual.
+
 ## Related
 
 - [Deployment construct](deployment.md) · [Run model](../schemas/run-model.md) for the
diff --git a/okf-bundle/log.md b/okf-bundle/log.md
index c062eaf..b2089a0 100644
--- a/okf-bundle/log.md
+++ b/okf-bundle/log.md
@@ -1,5 +1,8 @@
 # Update Log
 
+## 2026-09-08
+* Record why CDK construct tests share one outdir and why vitest's timeout is 30 s
+
 ## 2026-08-13
 * **Update**: Updated [Deferred and out of scope for v1](/deferred-and-out-of-scope.md).
 
diff --git a/package-lock.json b/package-lock.json
index 2511a11..8496681 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "millwright",
-  "version": "0.6.3",
+  "version": "0.7.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "millwright",
-      "version": "0.6.3",
+      "version": "0.7.0",
       "license": "MIT",
       "workspaces": [
         "packages/*"
@@ -2727,12 +2727,12 @@
     },
     "packages/millwright-cdk": {
       "name": "@copperbox/millwright-cdk",
-      "version": "0.6.2",
+      "version": "0.7.0",
       "license": "MIT",
       "dependencies": {
-        "@copperbox/millwright-cli": "^0.6.2",
-        "@copperbox/millwright-state": "^0.6.2",
-        "@copperbox/millwright-workflows": "^0.6.2",
+        "@copperbox/millwright-cli": "^0.7.0",
+        "@copperbox/millwright-state": "^0.7.0",
+        "@copperbox/millwright-workflows": "^0.7.0",
         "esbuild": "^0.28.0",
         "ssh2": "^1.17.0"
       },
@@ -2760,7 +2760,7 @@
     },
     "packages/millwright-cli": {
       "name": "@copperbox/millwright-cli",
-      "version": "0.6.2",
+      "version": "0.7.0",
       "license": "MIT",
       "dependencies": {
         "@aws-sdk/client-cloudwatch-logs": "^3.1108.0",
@@ -2773,8 +2773,8 @@
         "@aws-sdk/client-sfn": "^3.1108.0",
         "@aws-sdk/client-ssm": "^3.700.0",
         "@aws-sdk/lib-dynamodb": "^3.1108.0",
-        "@copperbox/millwright-state": "^0.6.2",
-        "@copperbox/millwright-workflows": "^0.6.2",
+        "@copperbox/millwright-state": "^0.7.0",
+        "@copperbox/millwright-workflows": "^0.7.0",
         "commander": "^12.1.0",
         "ssh2": "^1.17.0",
         "typescript": "^5.7.0"
@@ -2792,7 +2792,7 @@
     },
     "packages/millwright-state": {
       "name": "@copperbox/millwright-state",
-      "version": "0.6.2",
+      "version": "0.7.0",
       "license": "MIT",
       "engines": {
         "node": ">=20"
@@ -2800,7 +2800,7 @@
     },
     "packages/millwright-workflows": {
       "name": "@copperbox/millwright-workflows",
-      "version": "0.6.2",
+      "version": "0.7.0",
       "license": "MIT",
       "engines": {
         "node": ">=20"
diff --git a/package.json b/package.json
index ad0b294..e47b8da 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "millwright",
-  "version": "0.6.3",
+  "version": "0.7.0",
   "private": true,
   "description": "Millwright monorepo — polling-driven CI/CD in your own AWS account",
   "license": "MIT",
@@ -11,7 +11,9 @@
     "build": "npm run build --workspace @copperbox/millwright-state --workspace @copperbox/millwright-workflows --workspace @copperbox/millwright-cdk --workspace @copperbox/millwright-cli",
     "typecheck": "npm run typecheck --workspaces",
     "test": "vitest run",
-    "set-version": "node scripts/set-version.mjs"
+    "set-version": "node scripts/set-version.mjs",
+    "check-version": "node scripts/set-version.mjs --check",
+    "version": "node scripts/set-version.mjs && npm install --package-lock-only && git add -u package.json packages package-lock.json"
   },
   "devDependencies": {
     "@types/node": "^22.10.0",
diff --git a/packages/millwright-cdk/package.json b/packages/millwright-cdk/package.json
index 9204181..ff3a169 100644
--- a/packages/millwright-cdk/package.json
+++ b/packages/millwright-cdk/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@copperbox/millwright-cdk",
-  "version": "0.6.2",
+  "version": "0.7.0",
   "description": "The Millwright CDK construct — deploys the millwright control plane into your AWS account",
   "license": "MIT",
   "repository": {
@@ -23,9 +23,9 @@
     "test": "vitest run"
   },
   "dependencies": {
-    "@copperbox/millwright-cli": "^0.6.2",
-    "@copperbox/millwright-state": "^0.6.2",
-    "@copperbox/millwright-workflows": "^0.6.2",
+    "@copperbox/millwright-cli": "^0.7.0",
+    "@copperbox/millwright-state": "^0.7.0",
+    "@copperbox/millwright-workflows": "^0.7.0",
     "esbuild": "^0.28.0",
     "ssh2": "^1.17.0"
   },
diff --git a/packages/millwright-cdk/src/version.ts b/packages/millwright-cdk/src/version.ts
index d811ac7..a3545c8 100644
--- a/packages/millwright-cdk/src/version.ts
+++ b/packages/millwright-cdk/src/version.ts
@@ -1,5 +1,5 @@
 // Kept in lockstep with package.json by scripts/set-version.mjs — do not edit by hand.
-export const VERSION = '0.6.2';
+export const VERSION = '0.7.0';
 
 /**
  * Highest run-model schemaVersion this control plane accepts. Synth fails
diff --git a/packages/millwright-cdk/test/build-project.test.ts b/packages/millwright-cdk/test/build-project.test.ts
index 1a5ff25..c092da8 100644
--- a/packages/millwright-cdk/test/build-project.test.ts
+++ b/packages/millwright-cdk/test/build-project.test.ts
@@ -1,12 +1,13 @@
-import { App, Stack } from 'aws-cdk-lib';
+import { Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import * as logs from 'aws-cdk-lib/aws-logs';
 import * as s3 from 'aws-cdk-lib/aws-s3';
 import { describe, expect, it } from 'vitest';
 import { BuildProject } from '../src';
+import { testApp } from './support/test-app';
 
 function synth(): { buildProject: BuildProject; template: Template } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const buildProject = new BuildProject(stack, 'BuildProject', {
     deploymentName: 'ci',
     artifactBucket: new s3.Bucket(stack, 'Artifacts'),
diff --git a/packages/millwright-cdk/test/data-stores.test.ts b/packages/millwright-cdk/test/data-stores.test.ts
index 8bbbbbf..1af8f70 100644
--- a/packages/millwright-cdk/test/data-stores.test.ts
+++ b/packages/millwright-cdk/test/data-stores.test.ts
@@ -1,7 +1,8 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Annotations, Match, Template } from 'aws-cdk-lib/assertions';
 import { describe, expect, it } from 'vitest';
 import { Millwright, MillwrightProps } from '../src';
+import { testApp } from './support/test-app';
 
 const BOUNDARY_ARN = 'arn:aws:iam::123456789012:policy/team-boundary';
 
@@ -10,7 +11,7 @@ function templateFor(props: Partial<MillwrightProps> = {}): {
   millwright: Millwright;
   template: Template;
 } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const millwright = new Millwright(stack, 'Millwright', {
     permissionsBoundary: BOUNDARY_ARN,
     ...props,
@@ -169,7 +170,7 @@ describe('build log group (C17)', () => {
   });
 
   it('rejects retention day counts CloudWatch does not support', () => {
-    const stack = new Stack(new App(), 'Test');
+    const stack = new Stack(testApp(), 'Test');
     expect(
       () =>
         new Millwright(stack, 'Millwright', {
diff --git a/packages/millwright-cdk/test/event-bus.test.ts b/packages/millwright-cdk/test/event-bus.test.ts
index 7ddee0e..144b1c6 100644
--- a/packages/millwright-cdk/test/event-bus.test.ts
+++ b/packages/millwright-cdk/test/event-bus.test.ts
@@ -1,13 +1,14 @@
-import { App, Stack } from 'aws-cdk-lib';
+import { Stack } from 'aws-cdk-lib';
 import { Template } from 'aws-cdk-lib/assertions';
 import { describe, expect, it } from 'vitest';
 import { MillwrightEventBus } from '../src';
+import { testApp } from './support/test-app';
 
 function synth(deploymentName = 'millwright'): {
   bus: MillwrightEventBus;
   template: Template;
 } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const bus = new MillwrightEventBus(stack, 'EventBus', { deploymentName });
   return { bus, template: Template.fromStack(stack) };
 }
diff --git a/packages/millwright-cdk/test/launcher-construct.test.ts b/packages/millwright-cdk/test/launcher-construct.test.ts
index 792d124..9fdcc34 100644
--- a/packages/millwright-cdk/test/launcher-construct.test.ts
+++ b/packages/millwright-cdk/test/launcher-construct.test.ts
@@ -1,12 +1,13 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
 import * as s3 from 'aws-cdk-lib/aws-s3';
 import { describe, expect, it } from 'vitest';
 import { Launcher, MillwrightEventBus } from '../src';
+import { testApp } from './support/test-app';
 
 function synth(): { launcher: Launcher; template: Template } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const bus = new MillwrightEventBus(stack, 'EventBus', { deploymentName: 'ci' });
   const launcher = new Launcher(stack, 'Launcher', {
     deploymentName: 'ci',
diff --git a/packages/millwright-cdk/test/millwright.test.ts b/packages/millwright-cdk/test/millwright.test.ts
index 02d94ea..3a54258 100644
--- a/packages/millwright-cdk/test/millwright.test.ts
+++ b/packages/millwright-cdk/test/millwright.test.ts
@@ -1,32 +1,27 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Annotations, Match, Template } from 'aws-cdk-lib/assertions';
 import * as iam from 'aws-cdk-lib/aws-iam';
 import { describe, expect, it } from 'vitest';
 import { Boundary, Millwright, MillwrightProps, SUPPORTED_SCHEMA_VERSION, VERSION } from '../src';
-import cdkPkg from '../package.json';
-import rootPkg from '../../../package.json';
-import cliPkg from '../../millwright-cli/package.json';
-import statePkg from '../../millwright-state/package.json';
-import workflowsPkg from '../../millwright-workflows/package.json';
-import { VERSION as CLI_VERSION } from '../../millwright-cli/src/version';
+import { testApp } from './support/test-app';
 
 const BOUNDARY_ARN = 'arn:aws:iam::123456789012:policy/team-boundary';
 
 function stackWith(props: MillwrightProps): { stack: Stack; millwright: Millwright } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   return { stack, millwright: new Millwright(stack, 'Millwright', props) };
 }
 
 describe('permissionsBoundary', () => {
   it('throws at construct time when absent', () => {
-    const stack = new Stack(new App(), 'Test');
+    const stack = new Stack(testApp(), 'Test');
     expect(() => new Millwright(stack, 'Millwright', {} as MillwrightProps)).toThrow(
       /permissions boundary/i,
     );
   });
 
   it('throws on a value that is neither an ARN nor Boundary.NONE', () => {
-    const stack = new Stack(new App(), 'Test');
+    const stack = new Stack(testApp(), 'Test');
     expect(
       () => new Millwright(stack, 'Millwright', { permissionsBoundary: 'team-boundary' }),
     ).toThrow(/managed policy ARN or Boundary\.NONE/);
@@ -113,7 +108,7 @@ describe('manifest parameter', () => {
 
   it('rejects deployment names that cannot namespace SSM paths', () => {
     for (const bad of ['Millwright', 'has space', '-leading', 'a/b', '']) {
-      const stack = new Stack(new App(), 'Test');
+      const stack = new Stack(testApp(), 'Test');
       expect(
         () =>
           new Millwright(stack, 'Millwright', {
@@ -166,19 +161,3 @@ describe('run executor wiring', () => {
     expect(millwright.buildProject.projectName).toBe(millwright.runExecutor.buildProjectName);
   });
 });
-
-describe('lockstep version', () => {
-  it('keeps the embedded VERSION constants in sync with their manifests', () => {
-    expect(VERSION).toBe(cdkPkg.version);
-    expect(CLI_VERSION).toBe(cliPkg.version);
-  });
-
-  it('keeps every workspace manifest on the root version', () => {
-    // A hand-edited bump that skips `npm run set-version` moves some subset
-    // of the five manifests; pinning all four workspaces to the root catches
-    // any divergence, not just the cdk one.
-    for (const pkg of [cdkPkg, cliPkg, statePkg, workflowsPkg]) {
-      expect(pkg.version, pkg.name).toBe(rootPkg.version);
-    }
-  });
-});
diff --git a/packages/millwright-cdk/test/poller-construct.test.ts b/packages/millwright-cdk/test/poller-construct.test.ts
index ee4036c..a5a319a 100644
--- a/packages/millwright-cdk/test/poller-construct.test.ts
+++ b/packages/millwright-cdk/test/poller-construct.test.ts
@@ -1,16 +1,17 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Annotations, Match, Template } from 'aws-cdk-lib/assertions';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
 import * as kms from 'aws-cdk-lib/aws-kms';
 import { describe, expect, it } from 'vitest';
 import { MillwrightEventBus, Poller } from '../src';
+import { testApp } from './support/test-app';
 
 function synth(pollCadence = Duration.minutes(1)): {
   poller: Poller;
   stack: Stack;
   template: Template;
 } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const bus = new MillwrightEventBus(stack, 'EventBus', { deploymentName: 'ci' });
   const poller = new Poller(stack, 'Poller', {
     deploymentName: 'ci',
diff --git a/packages/millwright-cdk/test/reporter-construct.test.ts b/packages/millwright-cdk/test/reporter-construct.test.ts
index 0687d64..1e2287b 100644
--- a/packages/millwright-cdk/test/reporter-construct.test.ts
+++ b/packages/millwright-cdk/test/reporter-construct.test.ts
@@ -1,4 +1,4 @@
-import { App, Stack } from 'aws-cdk-lib';
+import { Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
 import * as kms from 'aws-cdk-lib/aws-kms';
@@ -6,9 +6,10 @@ import { describe, expect, it } from 'vitest';
 import { Reporter } from '../src';
 import { checkStateKey } from '@copperbox/millwright-state';
 import { coordinatesFromStreamRecords } from '../src/runtime/reporter/handler';
+import { testApp } from './support/test-app';
 
 function synth(): { reporter: Reporter; template: Template } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const reporter = new Reporter(stack, 'Reporter', {
     deploymentName: 'ci',
     stateTable: new dynamodb.Table(stack, 'StateTable', {
diff --git a/packages/millwright-cdk/test/run-executor-construct.test.ts b/packages/millwright-cdk/test/run-executor-construct.test.ts
index 5354dc3..9b50415 100644
--- a/packages/millwright-cdk/test/run-executor-construct.test.ts
+++ b/packages/millwright-cdk/test/run-executor-construct.test.ts
@@ -1,12 +1,13 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
 import * as s3 from 'aws-cdk-lib/aws-s3';
 import { describe, expect, it } from 'vitest';
 import { RunExecutor } from '../src';
+import { testApp } from './support/test-app';
 
 function synth(): { executor: RunExecutor; template: Template } {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const executor = new RunExecutor(stack, 'RunExecutor', {
     deploymentName: 'ci',
     stateTable: new dynamodb.Table(stack, 'StateTable', {
diff --git a/packages/millwright-cdk/test/shim-assets.test.ts b/packages/millwright-cdk/test/shim-assets.test.ts
index 1a50ac4..f60ad50 100644
--- a/packages/millwright-cdk/test/shim-assets.test.ts
+++ b/packages/millwright-cdk/test/shim-assets.test.ts
@@ -4,12 +4,13 @@ import { mkdtemp, readFile, rm } from 'node:fs/promises';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import { promisify } from 'node:util';
-import { App, Stack } from 'aws-cdk-lib';
+import { Stack } from 'aws-cdk-lib';
 import { Template } from 'aws-cdk-lib/assertions';
 import * as s3 from 'aws-cdk-lib/aws-s3';
 import { afterEach, beforeEach, describe, expect, it } from 'vitest';
 import cdkPkg from '../package.json';
 import { ShimAssets, stageShimDelivery } from '../src';
+import { testApp } from './support/test-app';
 
 const sh = promisify(execFile);
 
@@ -104,7 +105,7 @@ describe('release build', () => {
 
 describe('shim assets construct (C13)', () => {
   it('deploys the staged delivery to the artifact bucket under control/shim/', () => {
-    const stack = new Stack(new App(), 'Test');
+    const stack = new Stack(testApp(), 'Test');
     new ShimAssets(stack, 'ShimAssets', {
       deploymentName: 'ci',
       artifactBucket: new s3.Bucket(stack, 'Artifacts'),
diff --git a/packages/millwright-cdk/test/step-events-writer-construct.test.ts b/packages/millwright-cdk/test/step-events-writer-construct.test.ts
index 86875d1..6d7e193 100644
--- a/packages/millwright-cdk/test/step-events-writer-construct.test.ts
+++ b/packages/millwright-cdk/test/step-events-writer-construct.test.ts
@@ -1,11 +1,12 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
 import { describe, expect, it } from 'vitest';
 import { MillwrightEventBus, StepEventsWriter } from '../src';
+import { testApp } from './support/test-app';
 
 function synth(deploymentName = 'ci'): Template {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const bus = new MillwrightEventBus(stack, 'EventBus', { deploymentName });
   const table = new dynamodb.Table(stack, 'StateTable', {
     partitionKey: { name: 'pk', type: dynamodb.AttributeType.STRING },
diff --git a/packages/millwright-cdk/test/support/test-app.ts b/packages/millwright-cdk/test/support/test-app.ts
new file mode 100644
index 0000000..0ec1ac4
--- /dev/null
+++ b/packages/millwright-cdk/test/support/test-app.ts
@@ -0,0 +1,26 @@
+import { mkdtempSync, realpathSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { App, AppProps } from 'aws-cdk-lib';
+
+/**
+ * A CDK App for construct tests, with one cloud-assembly outdir shared by every
+ * App in this worker process.
+ *
+ * Synthesizing the Millwright construct bundles ten Lambdas with esbuild (plus
+ * the synth tooling bundle), which costs seconds per synth and blew vitest's
+ * 5 s per-test budget on the CI runner. aws-cdk-lib's AssetStaging keeps a
+ * process-wide cache keyed on (outdir, source, bundling options), but a bare
+ * `new App()` picks a fresh temp outdir every time, so nothing ever hits it.
+ * Pinning the outdir per process means the first synth in a test file does the
+ * bundling and every later synth reuses it.
+ *
+ * The outdir is not removed afterwards: a bare `new App()` also leaves its temp
+ * dir behind, once per App, so this strictly reduces the litter.
+ */
+let outdir: string | undefined;
+
+export function testApp(props: AppProps = {}): App {
+  outdir ??= mkdtempSync(join(realpathSync(tmpdir()), 'millwright-cdk-test-'));
+  return new App({ outdir, ...props });
+}
diff --git a/packages/millwright-cdk/test/sweep-construct.test.ts b/packages/millwright-cdk/test/sweep-construct.test.ts
index 1e00fe7..6b1bd66 100644
--- a/packages/millwright-cdk/test/sweep-construct.test.ts
+++ b/packages/millwright-cdk/test/sweep-construct.test.ts
@@ -1,13 +1,14 @@
-import { App, Duration, Stack } from 'aws-cdk-lib';
+import { Duration, Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
 import { describe, expect, it } from 'vitest';
 import { Sweep } from '../src';
+import { testApp } from './support/test-app';
 
 const RUN_EXECUTOR_ARN = 'arn:aws:states:eu-west-1:123456789012:stateMachine:ci-run-executor';
 
 function synth(deploymentName = 'ci'): Template {
-  const stack = new Stack(new App(), 'Test');
+  const stack = new Stack(testApp(), 'Test');
   const table = new dynamodb.Table(stack, 'StateTable', {
     partitionKey: { name: 'pk', type: dynamodb.AttributeType.STRING },
     sortKey: { name: 'sk', type: dynamodb.AttributeType.STRING },
diff --git a/packages/millwright-cdk/test/synth-job-construct.test.ts b/packages/millwright-cdk/test/synth-job-construct.test.ts
index e276052..5cf9957 100644
--- a/packages/millwright-cdk/test/synth-job-construct.test.ts
+++ b/packages/millwright-cdk/test/synth-job-construct.test.ts
@@ -1,8 +1,9 @@
-import { App, Stack } from 'aws-cdk-lib';
+import { Stack } from 'aws-cdk-lib';
 import { Match, Template } from 'aws-cdk-lib/assertions';
 import { beforeAll, describe, expect, it } from 'vitest';
 import { Millwright } from '../src/millwright';
 import { SYNTH_IMAGE } from '../src/synth-image';
+import { testApp } from './support/test-app';
 
 const BOUNDARY_ARN = 'arn:aws:iam::123456789012:policy/boundary';
 
@@ -10,7 +11,7 @@ let millwright: Millwright;
 let template: Template;
 
 beforeAll(() => {
-  const app = new App();
+  const app = testApp();
   const stack = new Stack(app, 'Test');
   millwright = new Millwright(stack, 'Millwright', { permissionsBoundary: BOUNDARY_ARN });
   template = Template.fromStack(stack);
diff --git a/packages/millwright-cli/package.json b/packages/millwright-cli/package.json
index 7bd81c8..9aae3a6 100644
--- a/packages/millwright-cli/package.json
+++ b/packages/millwright-cli/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@copperbox/millwright-cli",
-  "version": "0.6.2",
+  "version": "0.7.0",
   "description": "millwright CLI — operate a millwright deployment from operator and developer machines",
   "license": "MIT",
   "repository": {
@@ -33,8 +33,8 @@
     "@aws-sdk/client-sfn": "^3.1108.0",
     "@aws-sdk/client-ssm": "^3.700.0",
     "@aws-sdk/lib-dynamodb": "^3.1108.0",
-    "@copperbox/millwright-state": "^0.6.2",
-    "@copperbox/millwright-workflows": "^0.6.2",
+    "@copperbox/millwright-state": "^0.7.0",
+    "@copperbox/millwright-workflows": "^0.7.0",
     "commander": "^12.1.0",
     "ssh2": "^1.17.0",
     "typescript": "^5.7.0"
diff --git a/packages/millwright-cli/src/version.ts b/packages/millwright-cli/src/version.ts
index cf52011..88a9716 100644
--- a/packages/millwright-cli/src/version.ts
+++ b/packages/millwright-cli/src/version.ts
@@ -1,2 +1,2 @@
 // Kept in lockstep with package.json by scripts/set-version.mjs — do not edit by hand.
-export const VERSION = '0.6.2';
+export const VERSION = '0.7.0';
diff --git a/packages/millwright-cli/test/local-run.test.ts b/packages/millwright-cli/test/local-run.test.ts
index 5cdcce2..8f21504 100644
--- a/packages/millwright-cli/test/local-run.test.ts
+++ b/packages/millwright-cli/test/local-run.test.ts
@@ -73,11 +73,17 @@ interface JobPlan {
  */
 class FakeExecutor implements Executor {
   readonly started: LocalJobSpec[] = [];
+  private startWaiters: ((spec: LocalJobSpec) => void)[] = [];
 
   constructor(private readonly plans: Readonly<Record<string, JobPlan>> = {}) {}
 
   async preflight(): Promise<void> {}
 
+  /** Resolves when the next job container is started. */
+  nextStart(): Promise<LocalJobSpec> {
+    return new Promise((resolve) => this.startWaiters.push(resolve));
+  }
+
   private emit(spec: LocalJobSpec, status: string, extra: Record<string, unknown> = {}): void {
     fs.mkdirSync(path.dirname(spec.eventsFile), { recursive: true });
     const detail = {
@@ -96,6 +102,9 @@ class FakeExecutor implements Executor {
 
   start(spec: LocalJobSpec): LocalExecution {
     this.started.push(spec);
+    const waiters = this.startWaiters;
+    this.startWaiters = [];
+    for (const waiter of waiters) waiter(spec);
     const attempt = this.started.filter((s) => s.job === spec.job).length;
     const plan = this.plans[spec.job] ?? {};
     let stopRequested = false;
@@ -262,9 +271,13 @@ describe('millwright run — the local host', () => {
     const executor = new FakeExecutor({ build: { block: true } });
     const h = harness(root, executor);
 
+    const started = executor.nextStart();
     const run = localRun(h.deps, { workflow: 'ci' });
-    // Let the build container start, then interrupt.
-    await new Promise((resolve) => setTimeout(resolve, 40));
+    // Interrupt once the build container has started. A fixed sleep raced the
+    // run's setup (several real git subprocesses precede cancel registration):
+    // under load the cancel arrived before the handler existed, was dropped,
+    // and the blocked build never ended.
+    await started;
     h.cancel();
     const result = await run;
 
diff --git a/packages/millwright-state/package.json b/packages/millwright-state/package.json
index 1039b19..813e381 100644
--- a/packages/millwright-state/package.json
+++ b/packages/millwright-state/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@copperbox/millwright-state",
-  "version": "0.6.2",
+  "version": "0.7.0",
   "description": "Millwright's shared data-plane helpers — state/polling table item accessors, SSM config-plane paths, S3 layout",
   "license": "MIT",
   "repository": {
diff --git a/packages/millwright-workflows/package.json b/packages/millwright-workflows/package.json
index 870a7dc..f52ef08 100644
--- a/packages/millwright-workflows/package.json
+++ b/packages/millwright-workflows/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@copperbox/millwright-workflows",
-  "version": "0.6.2",
+  "version": "0.7.0",
   "description": "Millwright workflow definition library — the only install in watched repos",
   "license": "MIT",
   "repository": {
diff --git a/scripts/set-version.mjs b/scripts/set-version.mjs
index 448e58a..ceb06e1 100644
--- a/scripts/set-version.mjs
+++ b/scripts/set-version.mjs
@@ -1,22 +1,23 @@
 #!/usr/bin/env node
-// Lockstep version bump: all three packages (and the root) always share one
-// version, and the embedded src/version.ts constants track package.json.
+// Lockstep version bump: all four packages (and the root) always share one
+// version, every internal @copperbox/millwright-* dependency range is
+// ^<version>, and the embedded src/version.ts constants track package.json.
 //
-//   npm run set-version -- 0.2.0
+//   npm version 0.2.0              # bump everything to 0.2.0 (via the
+//                                  # root `version` lifecycle script)
+//   npm run set-version -- 0.2.0   # the same bump without npm version
+//   npm run set-version -- --check # verify the tree is in lockstep (CI)
+//
+// Under `npm version` the script takes no argument: npm exports the new
+// version as npm_package_version for every lifecycle script on every
+// platform, whereas `$npm_package_version` in package.json only expands
+// under a POSIX shell (cmd.exe hands it over as a literal).
 
 import { readFileSync, writeFileSync, existsSync } from 'node:fs';
 import { join, dirname } from 'node:path';
-import { fileURLToPath } from 'node:url';
-
-const root = join(dirname(fileURLToPath(import.meta.url)), '..');
-const version = process.argv[2];
+import { fileURLToPath, pathToFileURL } from 'node:url';
 
-if (!version || !/^\d+\.\d+\.\d+(-[0-9A-Za-z-.]+)?$/.test(version)) {
-  console.error('Usage: npm run set-version -- <semver>');
-  process.exit(1);
-}
-
-const packageDirs = [
+export const packageDirs = [
   '.',
   'packages/millwright-state',
   'packages/millwright-workflows',
@@ -24,24 +25,122 @@ const packageDirs = [
   'packages/millwright-cli',
 ];
 
-for (const dir of packageDirs) {
-  const manifestPath = join(root, dir, 'package.json');
-  const manifest = JSON.parse(readFileSync(manifestPath, 'utf8'));
-  manifest.version = version;
-  for (const block of ['dependencies', 'devDependencies', 'peerDependencies', 'optionalDependencies']) {
-    for (const dep of Object.keys(manifest[block] ?? {})) {
-      if (dep.startsWith('@copperbox/millwright-')) manifest[block][dep] = `^${version}`;
+const dependencyBlocks = ['dependencies', 'devDependencies', 'peerDependencies', 'optionalDependencies'];
+const internalScope = '@copperbox/millwright-';
+const versionPattern = /^\d+\.\d+\.\d+(-[0-9A-Za-z-.]+)?$/;
+const versionConstant = /export const VERSION = '([^']*)';/;
+
+function readManifest(root, dir) {
+  return JSON.parse(readFileSync(join(root, dir, 'package.json'), 'utf8'));
+}
+
+function versionTsPath(root, dir) {
+  const path = join(root, dir, 'src', 'version.ts');
+  return existsSync(path) ? path : undefined;
+}
+
+/**
+ * Rewrites every manifest and embedded VERSION constant under `root` to
+ * `version`. Returns one log line per manifest touched.
+ */
+export function applyVersion(root, version) {
+  const log = [];
+  for (const dir of packageDirs) {
+    const manifest = readManifest(root, dir);
+    manifest.version = version;
+    for (const block of dependencyBlocks) {
+      for (const dep of Object.keys(manifest[block] ?? {})) {
+        if (dep.startsWith(internalScope)) manifest[block][dep] = `^${version}`;
+      }
+    }
+    writeFileSync(join(root, dir, 'package.json'), `${JSON.stringify(manifest, null, 2)}\n`);
+    log.push(`${manifest.name} -> ${version}`);
+
+    const versionTs = versionTsPath(root, dir);
+    if (versionTs) {
+      const source = readFileSync(versionTs, 'utf8').replace(
+        versionConstant,
+        `export const VERSION = '${version}';`,
+      );
+      writeFileSync(versionTs, source);
     }
   }
-  writeFileSync(manifestPath, `${JSON.stringify(manifest, null, 2)}\n`);
-  console.log(`${manifest.name} -> ${version}`);
-
-  const versionTs = join(root, dir, 'src', 'version.ts');
-  if (existsSync(versionTs)) {
-    const source = readFileSync(versionTs, 'utf8').replace(
-      /export const VERSION = '[^']*';/,
-      `export const VERSION = '${version}';`,
-    );
-    writeFileSync(versionTs, source);
+  return log;
+}
+
+/**
+ * Compares every manifest and embedded VERSION constant under `root` against
+ * the root manifest's version. Returns the root version and one line per
+ * mismatch; an empty list means the tree is in lockstep.
+ */
+export function checkLockstep(root) {
+  const { version } = readManifest(root, '.');
+  const mismatches = [];
+  for (const dir of packageDirs) {
+    const manifestPath = join(dir, 'package.json');
+    const manifest = readManifest(root, dir);
+    if (manifest.version !== version) {
+      mismatches.push(`${manifestPath}: version is ${manifest.version}, expected ${version}`);
+    }
+    for (const block of dependencyBlocks) {
+      for (const [dep, range] of Object.entries(manifest[block] ?? {})) {
+        if (dep.startsWith(internalScope) && range !== `^${version}`) {
+          mismatches.push(`${manifestPath}: ${block}.${dep} is ${range}, expected ^${version}`);
+        }
+      }
+    }
+
+    const versionTs = versionTsPath(root, dir);
+    if (versionTs) {
+      const found = readFileSync(versionTs, 'utf8').match(versionConstant)?.[1];
+      if (found !== version) {
+        mismatches.push(`${join(dir, 'src', 'version.ts')}: VERSION is ${found ?? 'missing'}, expected ${version}`);
+      }
+    }
+  }
+  return { version, mismatches };
+}
+
+function usage() {
+  console.error('Usage: npm run set-version -- <semver>');
+  console.error('       npm run set-version -- --check');
+  console.error('       npm version <semver>   (reads npm_package_version)');
+  process.exit(1);
+}
+
+/**
+ * The version to apply: the positional argument, or, when running as npm's
+ * `version` lifecycle script, the freshly bumped npm_package_version.
+ */
+export function resolveVersion(positional, env) {
+  if (positional.length > 0) return positional[0];
+  if (env.npm_lifecycle_event === 'version') return env.npm_package_version;
+  return undefined;
+}
+
+function main(args) {
+  const root = join(dirname(fileURLToPath(import.meta.url)), '..');
+  const check = args.includes('--check');
+  const positional = args.filter((arg) => arg !== '--check');
+  if (positional.length > 1 || (check && positional.length > 0)) usage();
+
+  if (check) {
+    const { version, mismatches } = checkLockstep(root);
+    if (mismatches.length > 0) {
+      console.error(`Version lockstep broken (root is ${version}):`);
+      for (const line of mismatches) console.error(`  ${line}`);
+      console.error('Run `npm run set-version -- <semver>` to realign every package.');
+      process.exit(1);
+    }
+    console.log(`All packages in lockstep at ${version}.`);
+    return;
   }
+
+  const version = resolveVersion(positional, process.env);
+  if (!version || !versionPattern.test(version)) usage();
+  for (const line of applyVersion(root, version)) console.log(line);
+}
+
+if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
+  main(process.argv.slice(2));
 }
diff --git a/scripts/set-version.test.mjs b/scripts/set-version.test.mjs
new file mode 100644
index 0000000..25ce109
--- /dev/null
+++ b/scripts/set-version.test.mjs
@@ -0,0 +1,217 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { copyFileSync, mkdtempSync, mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { spawnSync } from 'node:child_process';
+import { applyVersion, checkLockstep, packageDirs, resolveVersion } from './set-version.mjs';
+
+const script = join(import.meta.dirname, 'set-version.mjs');
+
+const names = {
+  '.': 'millwright',
+  'packages/millwright-state': '@copperbox/millwright-state',
+  'packages/millwright-workflows': '@copperbox/millwright-workflows',
+  'packages/millwright-cdk': '@copperbox/millwright-cdk',
+  'packages/millwright-cli': '@copperbox/millwright-cli',
+};
+
+const internalDeps = {
+  'packages/millwright-cdk': {
+    dependencies: ['@copperbox/millwright-state', '@copperbox/millwright-workflows'],
+    devDependencies: ['@copperbox/millwright-cli'],
+  },
+  'packages/millwright-cli': {
+    dependencies: ['@copperbox/millwright-state', '@copperbox/millwright-workflows'],
+  },
+};
+
+const withVersionTs = new Set(['packages/millwright-cdk', 'packages/millwright-cli']);
+
+const tmpdirs = [];
+
+afterEach(() => {
+  for (const dir of tmpdirs.splice(0)) {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
+/** Builds a minimal lockstep tree at `version` and returns its root. */
+function fixture(version) {
+  const root = mkdtempSync(join(tmpdir(), 'set-version-'));
+  tmpdirs.push(root);
+  for (const dir of packageDirs) {
+    mkdirSync(join(root, dir), { recursive: true });
+    const manifest = { name: names[dir], version };
+    for (const [block, deps] of Object.entries(internalDeps[dir] ?? {})) {
+      manifest[block] = Object.fromEntries(deps.map((dep) => [dep, `^${version}`]));
+    }
+    manifest.devDependencies = { ...(manifest.devDependencies ?? {}), typescript: '^5.7.0' };
+    writeFileSync(join(root, dir, 'package.json'), `${JSON.stringify(manifest, null, 2)}\n`);
+    if (withVersionTs.has(dir)) {
+      mkdirSync(join(root, dir, 'src'), { recursive: true });
+      writeFileSync(
+        join(root, dir, 'src', 'version.ts'),
+        `// Kept in lockstep with package.json by scripts/set-version.mjs — do not edit by hand.\nexport const VERSION = '${version}';\n`,
+      );
+    }
+  }
+  return root;
+}
+
+function readManifest(root, dir) {
+  return JSON.parse(readFileSync(join(root, dir, 'package.json'), 'utf8'));
+}
+
+function writeManifest(root, dir, manifest) {
+  writeFileSync(join(root, dir, 'package.json'), `${JSON.stringify(manifest, null, 2)}\n`);
+}
+
+describe('checkLockstep', () => {
+  it('reports no mismatches for a tree in lockstep', () => {
+    const root = fixture('0.6.3');
+    expect(checkLockstep(root)).toEqual({ version: '0.6.3', mismatches: [] });
+  });
+
+  it('names a package whose version drifted from the root', () => {
+    const root = fixture('0.6.3');
+    const manifest = readManifest(root, 'packages/millwright-cli');
+    manifest.version = '0.6.2';
+    writeManifest(root, 'packages/millwright-cli', manifest);
+
+    const { mismatches } = checkLockstep(root);
+    expect(mismatches).toHaveLength(1);
+    expect(mismatches[0]).toContain('packages/millwright-cli/package.json');
+    expect(mismatches[0]).toContain('0.6.2');
+    expect(mismatches[0]).toContain('0.6.3');
+  });
+
+  it('names an internal dependency range that is not ^<root version>', () => {
+    const root = fixture('0.6.3');
+    const manifest = readManifest(root, 'packages/millwright-cdk');
+    manifest.devDependencies['@copperbox/millwright-cli'] = '^0.6.2';
+    writeManifest(root, 'packages/millwright-cdk', manifest);
+
+    const { mismatches } = checkLockstep(root);
+    expect(mismatches).toHaveLength(1);
+    expect(mismatches[0]).toContain('packages/millwright-cdk/package.json');
+    expect(mismatches[0]).toContain('devDependencies');
+    expect(mismatches[0]).toContain('@copperbox/millwright-cli');
+    expect(mismatches[0]).toContain('^0.6.2');
+    expect(mismatches[0]).toContain('^0.6.3');
+  });
+
+  it('ignores external dependency ranges', () => {
+    const root = fixture('0.6.3');
+    const manifest = readManifest(root, 'packages/millwright-cdk');
+    manifest.devDependencies.typescript = '^0.0.1';
+    writeManifest(root, 'packages/millwright-cdk', manifest);
+    expect(checkLockstep(root).mismatches).toEqual([]);
+  });
+
+  it('names an embedded VERSION constant that drifted', () => {
+    const root = fixture('0.6.3');
+    writeFileSync(
+      join(root, 'packages/millwright-cdk/src/version.ts'),
+      "export const VERSION = '0.6.2';\n",
+    );
+
+    const { mismatches } = checkLockstep(root);
+    expect(mismatches).toHaveLength(1);
+    expect(mismatches[0]).toContain('packages/millwright-cdk/src/version.ts');
+    expect(mismatches[0]).toContain('0.6.2');
+    expect(mismatches[0]).toContain('0.6.3');
+  });
+
+  it('lists every mismatch rather than stopping at the first', () => {
+    const root = fixture('0.6.3');
+    for (const dir of ['packages/millwright-state', 'packages/millwright-workflows']) {
+      const manifest = readManifest(root, dir);
+      manifest.version = '0.6.2';
+      writeManifest(root, dir, manifest);
+    }
+    writeFileSync(join(root, 'packages/millwright-cli/src/version.ts'), "export const VERSION = '0.5.0';\n");
+
+    const { mismatches } = checkLockstep(root);
+    expect(mismatches).toHaveLength(3);
+  });
+});
+
+describe('applyVersion', () => {
+  it('leaves a drifted tree in lockstep at the new version', () => {
+    const root = fixture('0.6.2');
+    const manifest = readManifest(root, 'packages/millwright-cli');
+    manifest.version = '0.5.0';
+    writeManifest(root, 'packages/millwright-cli', manifest);
+
+    applyVersion(root, '0.6.3');
+
+    expect(checkLockstep(root)).toEqual({ version: '0.6.3', mismatches: [] });
+    expect(readManifest(root, 'packages/millwright-cdk').dependencies['@copperbox/millwright-state']).toBe('^0.6.3');
+    expect(readFileSync(join(root, 'packages/millwright-cli/src/version.ts'), 'utf8')).toContain(
+      "export const VERSION = '0.6.3';",
+    );
+  });
+});
+
+describe('resolveVersion', () => {
+  it('reads npm_package_version only under the version lifecycle', () => {
+    const env = { npm_lifecycle_event: 'version', npm_package_version: '1.2.3' };
+    expect(resolveVersion([], env)).toBe('1.2.3');
+    expect(resolveVersion([], { ...env, npm_lifecycle_event: 'set-version' })).toBeUndefined();
+    expect(resolveVersion([], { npm_package_version: '1.2.3' })).toBeUndefined();
+    expect(resolveVersion(['0.9.0'], env)).toBe('0.9.0');
+  });
+});
+
+describe('command line', () => {
+  it('rejects a missing or malformed version', () => {
+    for (const args of [[], ['1.2']]) {
+      const result = spawnSync(process.execPath, [script, ...args], { encoding: 'utf8' });
+      expect(result.status, args.join(' ')).toBe(1);
+      expect(result.stderr).toContain('Usage:');
+    }
+  });
+
+  it('ignores npm_package_version outside the version lifecycle', () => {
+    const env = { ...process.env, npm_package_version: '1.2.3' };
+    delete env.npm_lifecycle_event;
+    const result = spawnSync(process.execPath, [script], { encoding: 'utf8', env });
+    expect(result.status).toBe(1);
+    expect(result.stderr).toContain('Usage:');
+  });
+
+  it('validates npm_package_version under the version lifecycle', () => {
+    const env = { ...process.env, npm_lifecycle_event: 'version', npm_package_version: 'not-a-version' };
+    const result = spawnSync(process.execPath, [script], { encoding: 'utf8', env });
+    expect(result.status).toBe(1);
+    expect(result.stderr).toContain('Usage:');
+  });
+
+  it('applies npm_package_version under the version lifecycle', () => {
+    // The script resolves its tree from its own location, so a copy inside a
+    // fixture rewrites the fixture rather than this checkout.
+    const root = fixture('0.6.3');
+    mkdirSync(join(root, 'scripts'));
+    copyFileSync(script, join(root, 'scripts', 'set-version.mjs'));
+    const env = { ...process.env, npm_lifecycle_event: 'version', npm_package_version: '0.7.0' };
+    const result = spawnSync(process.execPath, [join(root, 'scripts', 'set-version.mjs')], { encoding: 'utf8', env });
+    expect(result.stderr).toBe('');
+    expect(result.status).toBe(0);
+    expect(checkLockstep(root)).toEqual({ version: '0.7.0', mismatches: [] });
+  });
+
+  it('rejects --check combined with a version', () => {
+    const result = spawnSync(process.execPath, [script, '--check', '1.2.3'], { encoding: 'utf8' });
+    expect(result.status).toBe(1);
+    expect(result.stderr).toContain('Usage:');
+  });
+
+  it('passes --check against this repository', () => {
+    // The real tree is the one CI guards; this test is the only place the
+    // invariant is asserted, so a drift anywhere in the tree fails here.
+    const result = spawnSync(process.execPath, [script, '--check'], { encoding: 'utf8' });
+    expect(result.stderr).toBe('');
+    expect(result.status).toBe(0);
+    expect(result.stdout).toMatch(/lockstep at \d+\.\d+\.\d+/);
+  });
+});
diff --git a/vitest.config.ts b/vitest.config.ts
index 430d7c1..9f3cc45 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -4,6 +4,13 @@ import { defineConfig } from 'vitest/config';
 // Resolve workspace-internal imports to sources so tests run on a clean
 // checkout, without a prior `npm run build` producing each package's dist.
 export default defineConfig({
+  // The millwright-cdk construct tests synthesize real stacks, and each first
+  // synth in a file bundles ten Lambdas with esbuild (see
+  // packages/millwright-cdk/test/support/test-app.ts). That is several
+  // seconds on a loaded CI runner — well past vitest's 5 s default.
+  test: {
+    testTimeout: 30_000,
+  },
   resolve: {
     alias: {
       '@copperbox/millwright-state': path.resolve(