diff --git a/packages/playground/cli/src/mounts.ts b/packages/playground/cli/src/mounts.ts
index 2ae487294c..b8aceeddeb 100644
--- a/packages/playground/cli/src/mounts.ts
+++ b/packages/playground/cli/src/mounts.ts
@@ -107,7 +107,10 @@ const ACTIVATE_FIRST_THEME_STEP = {
  * Auto-mounts resolution logic:
  */
 export function expandAutoMounts(args: RunCLIArgs): RunCLIArgs {
-	const path = args.autoMount!;
+	if (typeof args.autoMount !== 'string') {
+		return args;
+	}
+	const path = args.autoMount;
 
 	const mount = [...(args.mount || [])];
 	const mountBeforeInstall = [...(args['mount-before-install'] || [])];
diff --git a/packages/playground/cli/src/run-cli.ts b/packages/playground/cli/src/run-cli.ts
index 3424d33af8..b991937cf6 100644
--- a/packages/playground/cli/src/run-cli.ts
+++ b/packages/playground/cli/src/run-cli.ts
@@ -433,11 +433,11 @@ export async function parseOptionsAndRunCLI(argsToParse: string[]) {
 				type: 'boolean',
 				default: false,
 			},
-			'no-auto-mount': {
+			'auto-mount': {
 				describe:
-					'Disable automatic project type detection. Use --mount to manually specify mounts instead.',
+					'Automatically detect project type (plugin, theme, wp-content, or WordPress) and mount accordingly. Use --no-auto-mount to disable and --mount to manually specify mounts instead.',
 				type: 'boolean',
-				default: false,
+				default: true,
 			},
 			// Define constants
 			define: sharedOptions['define'],
@@ -559,12 +559,20 @@ export async function parseOptionsAndRunCLI(argsToParse: string[]) {
 					}
 				}
 
-				if (args['auto-mount']) {
+				// For the `start` command, `--auto-mount` is a boolean
+				// toggle (path is taken from `--path`), so skip the
+				// directory validation here. Read the camelCase form for
+				// consistency with the rest of the codebase — yargs-parser
+				// emits both dashed and camelCase keys.
+				const autoMountArg = args['autoMount'];
+				if (
+					args._[0] !== 'start' &&
+					typeof autoMountArg === 'string' &&
+					autoMountArg
+				) {
 					let autoMountIsDir = false;
 					try {
-						const autoMountStats = fs.statSync(
-							args['auto-mount'] as string
-						);
+						const autoMountStats = fs.statSync(autoMountArg);
 						autoMountIsDir = autoMountStats.isDirectory();
 					} catch {
 						autoMountIsDir = false;
@@ -572,7 +580,7 @@ export async function parseOptionsAndRunCLI(argsToParse: string[]) {
 
 					if (!autoMountIsDir) {
 						throw new Error(
-							`The specified --auto-mount path is not a directory: '${args['auto-mount']}'.`
+							`The specified --auto-mount path is not a directory: '${autoMountArg}'.`
 						);
 					}
 				}
@@ -827,7 +835,13 @@ export interface RunCLIArgs {
 	quiet?: boolean;
 	verbosity?: LogVerbosity;
 	wp?: string;
-	autoMount?: string;
+	/**
+	 * For the `server` command (and other long-form commands), this is the
+	 * host path to auto-detect and mount. For the `start` command, this is a
+	 * boolean toggle: `true` (default) enables auto-detection on the
+	 * `--path` directory; `false` (i.e. `--no-auto-mount`) disables it.
+	 */
+	autoMount?: string | boolean;
 	pathAliases?: PathAlias[];
 	experimentalTrace?: boolean;
 	internalCookieStore?: boolean;
@@ -878,7 +892,6 @@ export interface RunCLIArgs {
 	// --------- Start command args -----------
 	path?: string;
 	skipBrowser?: boolean;
-	noAutoMount?: boolean;
 	reset?: boolean;
 }
 
@@ -1718,9 +1731,21 @@ function expandStartCommandArgs(
 	let newArgs = { ...args, command: 'server' };
 
 	/**
-	 * Enable auto-mount unless explicitly disabled
+	 * Enable auto-mount unless explicitly disabled via `--no-auto-mount`.
+	 *
+	 * yargs-parser's boolean-negation turns `--no-auto-mount` into
+	 * `{ autoMount: false }`, so `args.autoMount === false` is how we detect
+	 * the disabled case. The boolean form is start-command only — downstream
+	 * code treats `autoMount` as a string path, so drop it either way and
+	 * then re-populate it with a resolved path when enabled.
 	 */
-	if (!args.noAutoMount) {
+	const autoMountEnabled = args.autoMount !== false;
+	// Scrub both the camelCase and dashed forms yargs-parser emits so a
+	// stale boolean can't leak into downstream consumers that read either.
+	delete newArgs.autoMount;
+	delete (newArgs as Record<string, unknown>)['auto-mount'];
+
+	if (autoMountEnabled) {
 		newArgs.autoMount = path.resolve(process.cwd(), newArgs['path'] ?? '');
 		newArgs = expandAutoMounts(newArgs as RunCLIArgs);
 		// Delete the autoMount argument to avoid double expansion later on.
diff --git a/packages/playground/cli/tests/run-cli.spec.ts b/packages/playground/cli/tests/run-cli.spec.ts
index b4648b767b..308878393d 100644
--- a/packages/playground/cli/tests/run-cli.spec.ts
+++ b/packages/playground/cli/tests/run-cli.spec.ts
@@ -1067,6 +1067,56 @@ describe('start command', () => {
 		expect(existsSync(wpContentPath)).toBe(true);
 		expect(lstatSync(wpContentPath).isDirectory()).toBe(true);
 	}, 120000);
+
+	test('should accept --no-auto-mount and skip auto-detection', async () => {
+		// Regression test: yargs-parser's boolean-negation turns
+		// `--no-auto-mount` into `{ autoMount: false }`. When the start
+		// command declared a literal `no-auto-mount` option (with no
+		// matching `auto-mount`), strictOptions rejected the negated key
+		// with `Unknown arguments: auto-mount, autoMount`.
+		const tmpDir = await mkdtemp(
+			path.join(tmpdir(), 'playground-test-no-auto-mount-')
+		);
+		const pluginDirName = 'sample-plugin';
+		const pluginDir = path.join(tmpDir, pluginDirName);
+		mkdirSync(pluginDir, { recursive: true });
+		writeFileSync(
+			path.join(pluginDir, `${pluginDirName}.php`),
+			`<?php\n/*\nPlugin Name: Sample Plugin\n*/\n`
+		);
+
+		// Throw instead of no-op so any unexpected `process.exit` during
+		// startup fails the test loudly instead of silently continuing in
+		// an inconsistent state.
+		const exitSpy = vi.spyOn(process, 'exit').mockImplementation(((
+			code?: number | string | null
+		) => {
+			throw new Error(`process.exit unexpectedly called with "${code}"`);
+		}) as any);
+
+		try {
+			await using cliResult = await parseOptionsAndRunCLI([
+				'start',
+				`--path=${pluginDir}`,
+				'--no-auto-mount',
+				'--skip-browser',
+			]);
+			const cliServer = cliResult[internalsKeyForTesting].cliServer;
+
+			// Server started → yargs accepted `--no-auto-mount`.
+			expect(cliServer.serverUrl).toMatch(/^http:\/\/127\.0\.0\.1:\d+$/);
+
+			// Auto-mount did not fire → the plugin is not present under
+			// /wordpress/wp-content/plugins/.
+			const autoMountedPluginExists = await cliServer.playground.isDir(
+				`/wordpress/wp-content/plugins/${pluginDirName}`
+			);
+			expect(autoMountedPluginExists).toBe(false);
+		} finally {
+			exitSpy.mockRestore();
+			rmSync(tmpDir, { recursive: true, force: true });
+		}
+	}, 180000);
 });
 
 describe('php command', () => {