diff --git a/projects/plugins/boost/.phan/baseline.php b/projects/plugins/boost/.phan/baseline.php
index 5a24e570c060..c0e5586731a6 100644
--- a/projects/plugins/boost/.phan/baseline.php
+++ b/projects/plugins/boost/.phan/baseline.php
@@ -12,8 +12,8 @@
     // PhanTypeArraySuspiciousNullable : 15+ occurrences
     // PhanPluginDuplicateConditionalNullCoalescing : 10+ occurrences
     // PhanTypeArraySuspicious : 9 occurrences
-    // PhanTypeMismatchArgument : 6 occurrences
     // PhanUndeclaredConstant : 5 occurrences
+    // PhanTypeMismatchArgument : 4 occurrences
     // PhanTypeMismatchReturnProbablyReal : 4 occurrences
     // PhanUndeclaredClassConstant : 4 occurrences
     // PhanUndeclaredFunction : 4 occurrences
@@ -32,7 +32,7 @@
         'app/admin/class-config.php' => ['PhanTypeMismatchArgument'],
         'app/data-sync/class-minify-excludes-state-entry.php' => ['PhanTypeMismatchReturnProbablyReal'],
         'app/data-sync/class-performance-history-entry.php' => ['PhanPluginDuplicateConditionalNullCoalescing', 'PhanTypeArraySuspicious'],
-        'app/lib/class-cli.php' => ['PhanPluginDuplicateConditionalNullCoalescing', 'PhanTypeMismatchArgument'],
+        'app/lib/class-cli.php' => ['PhanPluginDuplicateConditionalNullCoalescing'],
         'app/lib/critical-css/class-critical-css-state.php' => ['PhanPluginDuplicateConditionalNullCoalescing', 'PhanTypeArraySuspiciousNullable'],
         'app/lib/minify/class-concatenate-css.php' => ['PhanPluginUseReturnValueInternalKnown', 'PhanTypeMismatchArgument'],
         'app/lib/minify/class-concatenate-js.php' => ['PhanPluginUseReturnValueInternalKnown', 'PhanTypeMismatchArgument'],
diff --git a/projects/plugins/boost/app/lib/class-cli.php b/projects/plugins/boost/app/lib/class-cli.php
index 494018c197ec..bfd0eac5eac1 100644
--- a/projects/plugins/boost/app/lib/class-cli.php
+++ b/projects/plugins/boost/app/lib/class-cli.php
@@ -28,7 +28,7 @@ class CLI {
 	 */
 	private $jetpack_boost;
 
-	const MAKE_E2E_TESTS_WORK_MODULES = array( 'critical_css', 'speculation_rules', 'render_blocking_js', 'page_cache', 'lcp', 'minify_js', 'minify_css', 'image_cdn', 'image_guide' );
+	const MAKE_E2E_TESTS_WORK_MODULES = array( 'critical_css', 'cloud_css', 'speculation_rules', 'render_blocking_js', 'page_cache', 'lcp', 'minify_js', 'minify_css', 'image_cdn', 'image_guide' );
 
 	/**
 	 * CLI constructor.
@@ -110,7 +110,7 @@ public function getting_started( $args ) {
 	 * Set a module status.
 	 *
 	 * @param string $module_slug Module slug.
-	 * @param string $status      Module status.
+	 * @param bool   $status      Module status.
 	 */
 	private function set_module_status( $module_slug, $status ) {
 		$modules = ( new Modules_Setup() )->get_available_modules_and_submodules();
@@ -122,7 +122,14 @@ private function set_module_status( $module_slug, $status ) {
 			);
 		}
 
-		$module->update( $status );
+		$updated = $module->update( $status );
+
+		// Fire the same action that the DataSync REST path fires (Modules_State_Entry::set),
+		// so CLI activation triggers module hooks like Cloud_CSS::activate() → Regenerate::start().
+		// Only fire when the status actually changed, matching the DataSync guard.
+		if ( $updated ) {
+			do_action( 'jetpack_boost_module_status_updated', $module_slug, $status );
+		}
 
 		if ( $module_slug === 'page_cache' && $status ) {
 			$setup_result = Page_Cache_Setup::run_setup();
@@ -142,10 +149,17 @@ private function set_module_status( $module_slug, $status ) {
 
 		$status_label = $status ? __( 'activated', 'jetpack-boost' ) : __( 'deactivated', 'jetpack-boost' );
 
-		/* translators: The %1$s refers to the module slug, %2$s refers to the module state (either activated or deactivated)*/
-		\WP_CLI::success(
-			sprintf( __( "'%1\$s' has been %2\$s.", 'jetpack-boost' ), $module_slug, $status_label )
-		);
+		if ( $updated ) {
+			/* translators: The %1$s refers to the module slug, %2$s refers to the module state (either activated or deactivated)*/
+			\WP_CLI::success(
+				sprintf( __( "'%1\$s' has been %2\$s.", 'jetpack-boost' ), $module_slug, $status_label )
+			);
+		} else {
+			/* translators: The %1$s refers to the module slug, %2$s refers to the module state (either activated or deactivated)*/
+			\WP_CLI::warning(
+				sprintf( __( "'%1\$s' was already %2\$s.", 'jetpack-boost' ), $module_slug, $status_label )
+			);
+		}
 	}
 
 	/**
diff --git a/projects/plugins/boost/changelog/add-boost-full-stack-e2e-infrastructure b/projects/plugins/boost/changelog/add-boost-full-stack-e2e-infrastructure
new file mode 100644
index 000000000000..f82d2506bd37
--- /dev/null
+++ b/projects/plugins/boost/changelog/add-boost-full-stack-e2e-infrastructure
@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Fix WP-CLI module activation not triggering side-effect hooks (e.g., Cloud CSS regeneration). Add full-stack E2E test infrastructure for the Boost Cloud pipeline.
diff --git a/projects/plugins/boost/tests/e2e/.gitignore b/projects/plugins/boost/tests/e2e/.gitignore
index b72d349f38d5..f5465a2fc9f0 100644
--- a/projects/plugins/boost/tests/e2e/.gitignore
+++ b/projects/plugins/boost/tests/e2e/.gitignore
@@ -6,4 +6,5 @@ plan-data.txt
 e2e_tunnels.txt
 jetpack-private-options.txt
 /allure-results
+/.state
 storage.json
diff --git a/projects/plugins/boost/tests/e2e/lib/fixtures/full-stack-test.ts b/projects/plugins/boost/tests/e2e/lib/fixtures/full-stack-test.ts
new file mode 100644
index 000000000000..c164baa7a9e3
--- /dev/null
+++ b/projects/plugins/boost/tests/e2e/lib/fixtures/full-stack-test.ts
@@ -0,0 +1,50 @@
+/**
+ * Playwright fixture for full-stack Boost E2E tests.
+ *
+ * Extends base-test from e2e-commons. The inherited beforeEach/afterEach hooks
+ * (WPCOM request counting) target the e2e container — harmless overhead when
+ * that container is running, which it typically is during local dev.
+ *
+ * Provides:
+ * - fullStackUtils (worker-scoped): Docker, Redis, WP-CLI operations against dev container
+ * - jetpackBoostPage (test-scoped): Boost admin page object
+ */
+
+import { test as baseTest, expect } from '_jetpack-e2e-commons/fixtures/base-test';
+import JetpackBoostPage from '../pages/jetpack-boost-page';
+import { FullStackUtils } from '../utils/full-stack-utils';
+
+const test = baseTest.extend<
+	{ jetpackBoostPage: JetpackBoostPage },
+	{ fullStackUtils: FullStackUtils }
+>( {
+	jetpackBoostPage: async ( { page }, use ) => {
+		await use( new JetpackBoostPage( page ) );
+	},
+	// Worker-scoped: one instance shared across all tests in a worker.
+	// Full-stack specs must use test.describe.serial because the shared Docker
+	// environment (dev WordPress, Redis, boost-cloud) cannot handle concurrent tests.
+	fullStackUtils: [
+		async ( {}, use ) => {
+			await use( new FullStackUtils() );
+		},
+		{ scope: 'worker' },
+	],
+} );
+
+// Capture Docker logs on test failure for post-mortem debugging in the Playwright HTML report.
+test.afterEach( async ( { fullStackUtils }, testInfo ) => {
+	if ( testInfo.status !== testInfo.expectedStatus ) {
+		try {
+			const logs = await fullStackUtils.captureDockerLogs();
+			await testInfo.attach( 'docker-logs', {
+				body: logs,
+				contentType: 'text/plain',
+			} );
+		} catch {
+			// Don't mask the real test failure
+		}
+	}
+} );
+
+export { test, expect };
diff --git a/projects/plugins/boost/tests/e2e/lib/full-stack-global-setup.ts b/projects/plugins/boost/tests/e2e/lib/full-stack-global-setup.ts
new file mode 100644
index 000000000000..b7162f94adbc
--- /dev/null
+++ b/projects/plugins/boost/tests/e2e/lib/full-stack-global-setup.ts
@@ -0,0 +1,193 @@
+/**
+ * Full-stack E2E test setup project.
+ *
+ * Performs health-check gates to verify the full-stack environment is ready,
+ * then authenticates against the dev WordPress and saves storage state.
+ *
+ * This file is referenced as a Playwright setup project in playwright.config.ts
+ * and runs before any full-stack test specs.
+ */
+
+import { mkdirSync, existsSync } from 'fs';
+import { dirname, join } from 'path';
+import { fileURLToPath } from 'url';
+import { test as setup, expect } from '@playwright/test';
+import {
+	getDevDomain,
+	executeDevWpCommand,
+	execDocker,
+	flushRedis,
+} from './utils/full-stack-utils';
+
+// Keep in sync with storageState path in playwright.config.ts fullStackProjects.
+const STORAGE_STATE_PATH = join(
+	dirname( fileURLToPath( import.meta.url ) ),
+	'..',
+	'.state',
+	'full-stack-storage-state.json'
+);
+
+setup( 'full-stack environment health check', async ( { request } ) => {
+	const boostCloudDir = process.env.BOOST_CLOUD_DIR;
+	// eslint-disable-next-line playwright/no-conditional-in-test
+	if ( ! boostCloudDir ) {
+		throw new Error(
+			'BOOST_CLOUD_DIR environment variable is required. ' +
+				'Set it to the path of your boost-cloud repository.'
+		);
+	}
+	const devDomain = getDevDomain();
+
+	// Gate 1: BOOST_CLOUD_DIR is valid
+	await setup.step( 'BOOST_CLOUD_DIR has docker-compose.yml', () => {
+		expect(
+			existsSync( join( boostCloudDir, 'docker-compose.yml' ) ),
+			`docker-compose.yml not found at ${ boostCloudDir }`
+		).toBe( true );
+	} );
+
+	// Gate 2: WordPress is alive
+	await setup.step( 'WordPress is reachable', async () => {
+		const response = await request.get( `http://${ devDomain }/`, {
+			maxRedirects: 0,
+			failOnStatusCode: false,
+		} );
+		expect(
+			[ 200, 301, 302 ],
+			`WordPress at http://${ devDomain }/ returned ${ response.status() }`
+		).toContain( response.status() );
+	} );
+
+	// Gate 3: Shield API is healthy.
+	// Uses localhost:1982 (host-side port mapping) — not boost-shield:1982 (Docker-internal).
+	// BOOST_DEV_DEFAULTS.shield_url uses the Docker hostname for container-to-container routing.
+	await setup.step( 'Shield API is healthy', async () => {
+		let healthy = false;
+		for ( let attempt = 0; attempt < 6; attempt++ ) {
+			try {
+				const response = await fetch( 'http://localhost:1982/v2/health', {
+					signal: AbortSignal.timeout( 5_000 ),
+				} );
+				const body = ( await response.json() ) as { status: string };
+				// eslint-disable-next-line playwright/no-conditional-in-test
+				if ( body.status === 'ok' ) {
+					healthy = true;
+					break;
+				}
+			} catch {
+				// Shield may be starting up
+			}
+			await new Promise( resolve => setTimeout( resolve, 5_000 ) );
+		}
+		expect( healthy, 'Shield health check at localhost:1982/v2/health did not return ok' ).toBe(
+			true
+		);
+	} );
+
+	// Gate 4: Redis is reachable
+	await setup.step( 'Redis is reachable', async () => {
+		const output = await execDocker( [
+			'compose',
+			'-f',
+			`${ boostCloudDir }/docker-compose.yml`,
+			'exec',
+			'-T',
+			'redis',
+			'redis-cli',
+			'ping',
+		] );
+		expect( output, 'Redis did not respond with PONG' ).toContain( 'PONG' );
+	} );
+
+	// Gate 5: Hydra can reach WordPress
+	await setup.step( 'Hydra can reach WordPress', async () => {
+		const output = await execDocker( [
+			'compose',
+			'-f',
+			`${ boostCloudDir }/docker-compose.yml`,
+			'exec',
+			'-T',
+			'boost-hydra-css',
+			'curl',
+			'-s',
+			'-o',
+			'/dev/null',
+			'-w',
+			'%{http_code}',
+			`http://${ devDomain }/`,
+		] );
+		// Extract 3-digit HTTP status code — execDocker concatenates stdout+stderr,
+		// so Docker Compose warnings may surround curl's status code output.
+		const match = output.match( /\b[1-5]\d{2}\b/ );
+		expect(
+			match,
+			`No HTTP status code found in Docker output: ${ output.slice( 0, 200 ) }`
+		).not.toBeNull();
+		const httpCode = parseInt( match![ 0 ], 10 );
+		expect(
+			[ 200, 301, 302 ],
+			`Hydra got HTTP ${ httpCode } reaching http://${ devDomain }/`
+		).toContain( httpCode );
+	} );
+
+	// Gate 6: boost-developer plugin is active
+	await setup.step( 'boost-developer plugin is active', async () => {
+		const output = await executeDevWpCommand( 'plugin list --status=active --format=json' );
+		const plugins = JSON.parse( output.trim() ) as Array< { name: string } >;
+		const names = plugins.map( p => p.name );
+		expect( names, 'boost-developer plugin is not active' ).toContain( 'boost-developer' );
+	} );
+
+	// Gate 7: No debug-critical-css-providers.php mu-plugin
+	await setup.step( 'debug-critical-css-providers mu-plugin is not present', async () => {
+		const output = await executeDevWpCommand( [
+			'eval',
+			"echo file_exists(WPMU_PLUGIN_DIR . '/debug-critical-css-providers.php') ? 'EXISTS' : 'NOT_FOUND';",
+		] );
+		expect(
+			output.trim(),
+			'debug-critical-css-providers.php is present in mu-plugins. ' +
+				'This file hardcodes external CSS provider URLs (wincityvoices.org), ' +
+				'causing Hydra to generate CSS for the wrong site. ' +
+				'Remove it: rm tools/docker/mu-plugins/debug-critical-css-providers.php'
+		).toContain( 'NOT_FOUND' );
+	} );
+
+	// Gate 8: Flush Redis to clear stale BullMQ jobs from interrupted prior runs
+	await setup.step( 'Flush Redis', async () => {
+		await flushRedis( boostCloudDir );
+	} );
+
+	// Gate 9: Authenticate against dev WordPress and save storage state
+	await setup.step( 'Authenticate against dev WordPress', async () => {
+		const loginResponse = await request.post( `http://${ devDomain }/wp-login.php`, {
+			form: {
+				log: 'jp_docker_acct',
+				pwd: 'jp_docker_pass',
+				rememberme: 'forever',
+				'wp-submit': 'Log In',
+				redirect_to: `http://${ devDomain }/wp-admin/`,
+			},
+		} );
+		expect(
+			loginResponse.ok() || loginResponse.status() === 302,
+			`Login failed with status ${ loginResponse.status() }`
+		).toBe( true );
+
+		// Verify authentication by requesting an admin page — a 200 with the login
+		// form would be a false positive from the POST above.
+		const adminResponse = await request.get( `http://${ devDomain }/wp-admin/profile.php` );
+		expect(
+			adminResponse.url(),
+			'Authentication failed: admin request was redirected to the login page'
+		).not.toContain( 'wp-login.php' );
+
+		// Save storage state for the full-stack test project
+		const stateDir = dirname( STORAGE_STATE_PATH );
+		// eslint-disable-next-line playwright/no-conditional-in-test
+		if ( ! existsSync( stateDir ) ) {
+			mkdirSync( stateDir, { recursive: true } );
+		}
+		await request.storageState( { path: STORAGE_STATE_PATH } );
+	} );
+} );
diff --git a/projects/plugins/boost/tests/e2e/lib/utils/full-stack-utils.ts b/projects/plugins/boost/tests/e2e/lib/utils/full-stack-utils.ts
new file mode 100644
index 000000000000..d8dc70e10edd
--- /dev/null
+++ b/projects/plugins/boost/tests/e2e/lib/utils/full-stack-utils.ts
@@ -0,0 +1,332 @@
+/**
+ * Full-stack test utilities for Jetpack Boost.
+ *
+ * Provides Docker-aware operations, WP-CLI polling, and Redis management
+ * for full-stack E2E tests that exercise the complete cloud pipeline
+ * (WordPress → Shield → Redis → Hydra → callback).
+ *
+ * Targets the dev WordPress container (not e2e) because boost-cloud services
+ * run on the jetpack_dev_default Docker network.
+ */
+
+import { execFile } from 'child_process';
+import { readFileSync, existsSync } from 'fs';
+import { join } from 'path';
+import { promisify } from 'util';
+import { executeCommand } from '_jetpack-e2e-commons/utils/cli';
+
+const execFileAsync = promisify( execFile );
+
+/**
+ * All 19 keys from boost-developer.php:50-69.
+ * boost_dev_get() sets any missing key to `false` (not the default) when the option exists,
+ * so ALL keys must be present. Missing `local_shield` = false breaks Shield routing.
+ */
+export const BOOST_DEV_DEFAULTS: Record< string, string | number | boolean > = {
+	cornerstone_pages_plan: 'default',
+	css_mode: 'default',
+	local_shield: 'on',
+	shield_url: 'http://boost-shield:1982',
+	client_id: 'boost-plugin',
+	client_secret: 'plugin-secret',
+	skip_check: false,
+	force_error: 'none',
+	docker_urls: false,
+	mobile_score: 80,
+	desktop_score: 90,
+	fake_speed_score: 'off',
+	datasync_debug: 'off',
+	site_url: '',
+	custom_site_url: '',
+	wpcom_token: '',
+	proxy_host: '',
+	proxy_port: '',
+	lcp_element: '',
+};
+
+/**
+ * Read DEV_DOMAIN from the boost-cloud .env file.
+ *
+ * @return {string} The dev domain, or 'jetpack-boost.test' as fallback.
+ */
+export function getDevDomain(): string {
+	const dir = process.env.BOOST_CLOUD_DIR;
+	if ( ! dir ) {
+		return 'jetpack-boost.test';
+	}
+	try {
+		const envContent = readFileSync( join( dir, '.env' ), 'utf8' );
+		const match = envContent.match( /^DEV_DOMAIN=(.+)$/m );
+		return match?.[ 1 ]?.trim().replace( /^["']|["']$/g, '' ) ?? 'jetpack-boost.test';
+	} catch {
+		return 'jetpack-boost.test';
+	}
+}
+
+/**
+ * Execute a WP-CLI command against the dev WordPress container.
+ *
+ * Uses `pnpm jetpack docker wp --` (no --type e2e --name t1) to target the dev container.
+ * Passes --url to ensure home_url() returns the correct domain instead of http://localhost
+ * (wp-config.php:99 sets WP_HOME='http://localhost' when HTTP_HOST is empty in Docker).
+ *
+ * **Use array form for commands with spaces in arguments** (JSON values, `wp eval` code, etc.).
+ * The string form splits on whitespace, matching the e2e-commons `executeCommand` convention,
+ * but will break quoted/space-containing args.
+ *
+ * @param  command - WP-CLI command string or argument array.
+ * @return {Promise<string>} Command stdout.
+ */
+export async function executeDevWpCommand( command: string | string[] ): Promise< string > {
+	const devDomain = getDevDomain();
+	const base = [ 'pnpm', 'jetpack', 'docker', 'wp', '--', `--url=http://${ devDomain }` ];
+	if ( Array.isArray( command ) ) {
+		return executeCommand( [ ...base, ...command ] );
+	}
+	return executeCommand( [ ...base, ...command.trim().split( /\s+/ ) ] );
+}
+
+/**
+ * Execute a Jetpack Boost CLI command against the dev WordPress container.
+ *
+ * @param  command - Boost CLI subcommand string or argument array.
+ * @return {Promise<string>} Command stdout.
+ */
+export async function executeDevJetpackBoostCommand(
+	command: string | string[]
+): Promise< string > {
+	if ( Array.isArray( command ) ) {
+		return executeDevWpCommand( [ 'jetpack-boost', ...command ] );
+	}
+	return executeDevWpCommand( `jetpack-boost ${ command }` );
+}
+
+/**
+ * Execute a Docker CLI command via child_process.execFile.
+ * Uses execFile directly because the e2e-commons executeCommand allowlist
+ * (wp, pnpm, sh) does not include docker. execFile is safe against
+ * shell injection (no shell expansion).
+ *
+ * @param  args - Arguments passed to the docker CLI.
+ * @return {Promise<string>} Combined stdout and stderr.
+ */
+export async function execDocker( args: string[] ): Promise< string > {
+	try {
+		const { stdout, stderr } = await execFileAsync( 'docker', args, {
+			timeout: 30_000,
+		} );
+		return stdout + stderr;
+	} catch ( error ) {
+		const msg = String( error );
+		if ( msg.includes( 'ENOENT' ) ) {
+			throw new Error( 'Docker not found. Is Docker installed and in your PATH?' );
+		}
+		if ( msg.includes( 'Cannot connect' ) || msg.includes( 'connect ECONNREFUSED' ) ) {
+			throw new Error(
+				'Docker daemon is not running. Start Docker Desktop or the Docker service.'
+			);
+		}
+		throw error;
+	}
+}
+
+/**
+ * Flush all Redis data in the boost-cloud Docker stack.
+ * Clears BullMQ job queues and dedup locks.
+ *
+ * @param boostCloudDir - Path to the boost-cloud repository.
+ */
+export async function flushRedis( boostCloudDir: string ): Promise< void > {
+	await execDocker( [
+		'compose',
+		'-f',
+		`${ boostCloudDir }/docker-compose.yml`,
+		'exec',
+		'-T',
+		'redis',
+		'redis-cli',
+		'FLUSHALL',
+	] );
+}
+
+/**
+ * Full-stack test utilities class.
+ * Worker-scoped in the Playwright fixture (one instance per worker).
+ */
+export class FullStackUtils {
+	private boostCloudDir: string;
+
+	constructor() {
+		const dir = process.env.BOOST_CLOUD_DIR;
+		if ( ! dir ) {
+			throw new Error(
+				'BOOST_CLOUD_DIR environment variable is required. ' +
+					'Set it to the path of your boost-cloud repository.'
+			);
+		}
+		if ( ! existsSync( join( dir, 'docker-compose.yml' ) ) ) {
+			throw new Error(
+				`BOOST_CLOUD_DIR is set to '${ dir }' but docker-compose.yml was not found there.`
+			);
+		}
+		this.boostCloudDir = dir;
+	}
+
+	/**
+	 * Reset the full-stack environment to a clean state.
+	 *
+	 * wp jetpack-boost reset is a FULL UNINSTALL: deletes all jetpack_boost_% options via SQL,
+	 * clears CSS storage posts, and removes transients. boost_dev survives (no jetpack_boost_ prefix).
+	 */
+	async resetFullStackEnvironment(): Promise< void > {
+		// Full reset (uninstall + deactivate)
+		await executeDevWpCommand( 'jetpack-boost reset' );
+
+		// Ensure both plugins are active
+		await executeDevWpCommand( 'plugin activate jetpack-boost boost-developer' );
+
+		// Deactivate mock plugins that may be left from prior e2e test runs
+		try {
+			await executeDevWpCommand(
+				'plugin deactivate e2e-mock-boost-connection e2e-mock-speed-score-api e2e-mock-premium-features'
+			);
+		} catch ( error ) {
+			// Expected when mock plugins are not installed; log other errors for debugging.
+			console.debug( 'Mock plugin deactivation (non-fatal):', String( error ) );
+		}
+
+		// Write all 19 boost_dev keys with correct defaults
+		await executeDevWpCommand( [
+			'option',
+			'update',
+			'boost_dev',
+			JSON.stringify( BOOST_DEV_DEFAULTS ),
+			'--format=json',
+		] );
+
+		// Clear Redis to prevent BullMQ dedup hangs from stale jobs
+		await this.flushRedis();
+	}
+
+	/**
+	 * Flush all Redis data. Clears BullMQ job queues and dedup locks.
+	 */
+	async flushRedis(): Promise< void > {
+		await flushRedis( this.boostCloudDir );
+	}
+
+	/**
+	 * Poll WP-CLI for Critical CSS generation completion.
+	 *
+	 * Option: jetpack_boost_ds_critical_css_state (wp-js-data-sync.php:17 + class-critical-css.php:92)
+	 * States: not_generated → pending → generated | error (class-critical-css-state.php:9-14)
+	 *
+	 * @param timeout - Maximum wait time in milliseconds.
+	 */
+	async waitForCssGeneration( timeout = 120_000 ): Promise< void > {
+		const pollInterval = 5_000;
+		const start = Date.now();
+		let lastState = 'unknown';
+
+		while ( Date.now() - start < timeout ) {
+			try {
+				const output = await executeDevWpCommand(
+					'option get jetpack_boost_ds_critical_css_state --format=json'
+				);
+				const state = JSON.parse( output.trim() );
+				lastState = JSON.stringify( state );
+
+				if ( state?.status === 'generated' ) {
+					return;
+				}
+
+				if ( state?.status === 'error' ) {
+					const errorMsg = state?.status_error ?? 'Unknown error';
+					throw new Error( `CSS generation failed: ${ errorMsg }` );
+				}
+			} catch ( error ) {
+				if ( error instanceof Error && error.message.startsWith( 'CSS generation failed' ) ) {
+					throw error;
+				}
+				// Option may not exist yet, keep polling
+			}
+
+			await new Promise( resolve => setTimeout( resolve, pollInterval ) );
+		}
+
+		// Timeout — capture diagnostics
+		let logs = '';
+		try {
+			logs = await this.captureDockerLogs();
+		} catch {
+			// Best effort
+		}
+
+		throw new Error(
+			`CSS generation timed out after ${ timeout / 1000 }s. ` +
+				`Last state: ${ lastState }. ` +
+				`Docker logs:\n${ logs.slice( 0, 2000 ) }`
+		);
+	}
+
+	/**
+	 * Update a single key in the boost_dev WordPress option.
+	 *
+	 * @param key   - Option key within the boost_dev object.
+	 * @param value - New value for the key.
+	 */
+	async setBoostDevOption( key: string, value: unknown ): Promise< void > {
+		const output = await executeDevWpCommand( 'option get boost_dev --format=json' );
+		const current = JSON.parse( output.trim() );
+		current[ key ] = value;
+		await executeDevWpCommand( [
+			'option',
+			'update',
+			'boost_dev',
+			JSON.stringify( current ),
+			'--format=json',
+		] );
+	}
+
+	/**
+	 * Capture recent Docker logs from Shield and Hydra CSS services.
+	 * Wrapped in error handling to avoid masking real test failures.
+	 *
+	 * @return {Promise<string>} Combined stdout and stderr from the log tail.
+	 */
+	async captureDockerLogs(): Promise< string > {
+		return execDocker( [
+			'compose',
+			'-f',
+			`${ this.boostCloudDir }/docker-compose.yml`,
+			'logs',
+			'--tail=200',
+			'boost-shield',
+			'boost-hydra-css',
+		] );
+	}
+
+	/**
+	 * Activate one or more Boost modules on the dev WordPress container.
+	 *
+	 * @param modules - Module slug(s) to activate.
+	 */
+	async activateModule( modules: string | string[] ): Promise< void > {
+		const moduleArray = Array.isArray( modules ) ? modules : [ modules ];
+		for ( const mod of moduleArray ) {
+			await executeDevJetpackBoostCommand( `module activate ${ mod }` );
+		}
+	}
+
+	/**
+	 * Deactivate one or more Boost modules on the dev WordPress container.
+	 *
+	 * @param modules - Module slug(s) to deactivate.
+	 */
+	async deactivateModule( modules: string | string[] ): Promise< void > {
+		const moduleArray = Array.isArray( modules ) ? modules : [ modules ];
+		for ( const mod of moduleArray ) {
+			await executeDevJetpackBoostCommand( `module deactivate ${ mod }` );
+		}
+	}
+}
diff --git a/projects/plugins/boost/tests/e2e/playwright.config.ts b/projects/plugins/boost/tests/e2e/playwright.config.ts
index 6f3d7983c8c1..34e325d246f9 100644
--- a/projects/plugins/boost/tests/e2e/playwright.config.ts
+++ b/projects/plugins/boost/tests/e2e/playwright.config.ts
@@ -1,5 +1,62 @@
+import { readFileSync } from 'fs';
+import { join } from 'path';
 import baseConfig, { setupProjects } from '_jetpack-e2e-commons/playwright.config.default';
 
+/**
+ * Read DEV_DOMAIN from the boost-cloud .env file for full-stack test baseURL.
+ * Falls back to 'jetpack-boost.test' if BOOST_CLOUD_DIR is not set or .env is unreadable.
+ *
+ * Intentionally duplicated from lib/utils/full-stack-utils.ts to avoid pulling
+ * test utility imports into config evaluation.
+ *
+ * @return {string} The dev domain, or 'jetpack-boost.test' as fallback.
+ */
+function getDevDomain(): string {
+	const dir = process.env.BOOST_CLOUD_DIR;
+	if ( ! dir ) {
+		return 'jetpack-boost.test';
+	}
+	try {
+		const env = readFileSync( join( dir, '.env' ), 'utf8' );
+		return (
+			env
+				.match( /^DEV_DOMAIN=(.+)$/m )?.[ 1 ]
+				?.trim()
+				.replace( /^["']|["']$/g, '' ) ?? 'jetpack-boost.test'
+		);
+	} catch {
+		return 'jetpack-boost.test';
+	}
+}
+
+// Full-stack projects are only registered when BOOST_CLOUD_DIR is set.
+// Playwright treats skipped setup projects as successful, so dependent projects
+// would still run and fail — conditional registration is the only safe approach.
+const fullStackProjects = process.env.BOOST_CLOUD_DIR
+	? [
+			{
+				name: 'full-stack setup',
+				testDir: './lib',
+				testMatch: 'full-stack-global-setup.ts',
+				dependencies: [ 'environment check' ],
+				storageState: undefined as undefined,
+			},
+			{
+				name: 'full-stack',
+				testMatch: '**/specs/full-stack/**',
+				dependencies: [ 'full-stack setup' ],
+				// Force single worker — full-stack tests mutate shared state
+				// (dev WordPress, boost-cloud Redis) and cannot run in parallel.
+				workers: 1,
+				use: {
+					baseURL: `http://${ getDevDomain() }`,
+					// Keep in sync with STORAGE_STATE_PATH in lib/full-stack-global-setup.ts.
+					storageState: '.state/full-stack-storage-state.json',
+				},
+			},
+	  ]
+	: [];
+
 export default {
 	...baseConfig,
 	use: {
@@ -11,7 +68,9 @@ export default {
 		{
 			name: 'jetpack boost e2e',
 			testMatch: '**/specs/**',
+			testIgnore: '**/specs/full-stack/**',
 			dependencies: [ 'global authentication' ],
 		},
+		...fullStackProjects,
 	],
 };
diff --git a/projects/plugins/boost/tests/e2e/specs/full-stack/critical-css.test.ts b/projects/plugins/boost/tests/e2e/specs/full-stack/critical-css.test.ts
new file mode 100644
index 000000000000..581af121ec67
--- /dev/null
+++ b/projects/plugins/boost/tests/e2e/specs/full-stack/critical-css.test.ts
@@ -0,0 +1,55 @@
+/**
+ * Full-stack Critical CSS generation test.
+ *
+ * Exercises the complete cloud pipeline:
+ * WordPress → Shield → Redis → Hydra (Chromium) → callback → WordPress
+ *
+ * Requires: Jetpack dev Docker + boost-cloud Docker + boost-developer plugin
+ */
+
+import { test, expect } from '../../lib/fixtures/full-stack-test';
+
+test.describe.serial( 'Full-stack Critical CSS generation', () => {
+	test.beforeAll( async ( { fullStackUtils } ) => {
+		await fullStackUtils.resetFullStackEnvironment();
+
+		// Set cloud CSS mode so boost-developer enables the cloud-critical-css feature
+		// (Actions.php adds jetpack_boost_has_feature_cloud-critical-css filter when css_mode === 'cloud')
+		await fullStackUtils.setBoostDevOption( 'css_mode', 'cloud' );
+
+		// Activating cloud_css triggers Cloud_CSS::activate() → Regenerate::start()
+		// via the jetpack_boost_module_status_updated action in the CLI.
+		// This sends a CSS generation request to Shield immediately.
+		await fullStackUtils.activateModule( 'cloud_css' );
+	} );
+
+	test( 'generates Critical CSS via Shield and Hydra', async ( {
+		fullStackUtils,
+		jetpackBoostPage,
+		page,
+	} ) => {
+		// Poll WP-CLI for CSS generation completion.
+		// Option: jetpack_boost_ds_critical_css_state (wp-js-data-sync.php:17 + class-critical-css.php:92)
+		// States: not_generated → pending → generated | error (class-critical-css-state.php:9-14)
+		await fullStackUtils.waitForCssGeneration( 120_000 );
+
+		// Verify the admin UI shows generation metadata.
+		// Test ID: data-testid="critical-css-meta" (status/status.tsx:59)
+		await jetpackBoostPage.visit();
+		await expect( page.getByTestId( 'critical-css-meta' ) ).toBeVisible( {
+			timeout: 30_000,
+		} );
+	} );
+
+	test( 'Critical CSS is present on the frontend', async ( { page } ) => {
+		await page.goto( '/' );
+
+		// Selector: <style id="jetpack-boost-critical-css"> (class-display-critical-css.php:108)
+		const styles = page.locator( '#jetpack-boost-critical-css' );
+		await expect( styles ).toBeAttached();
+
+		// textContent() preferred over innerText() for <style> elements (no layout reflow)
+		const content = await styles.textContent();
+		expect( content?.length ?? 0 ).toBeGreaterThan( 50 );
+	} );
+} );