fix: use Playwright MCP --executable-path flag (kebab-case)

Extract buildMcpArgs() helper and fix --executablePath → --executable-path
to match the Playwright MCP CLI's expected flag format.

Closes #16

Co-authored-by: KasumiChen <KasumiChen@users.noreply.github.com>

src/browser.test.ts

@@ -49,6 +49,25 @@ describe('browser helpers', () => {
     expect(__test__.appendLimited('12345', '67890', 8)).toBe('34567890');
   });
 
+  it('builds Playwright MCP args with kebab-case executable path', () => {
+    expect(__test__.buildMcpArgs({
+      mcpPath: '/tmp/cli.js',
+      executablePath: '/mnt/c/Program Files/Google/Chrome/Application/chrome.exe',
+    })).toEqual([
+      '/tmp/cli.js',
+      '--extension',
+      '--executable-path',
+      '/mnt/c/Program Files/Google/Chrome/Application/chrome.exe',
+    ]);
+
+    expect(__test__.buildMcpArgs({
+      mcpPath: '/tmp/cli.js',
+    })).toEqual([
+      '/tmp/cli.js',
+      '--extension',
+    ]);
+  });
+
   it('times out slow promises', async () => {
     await expect(__test__.withTimeout(new Promise(() => {}), 10, 'timeout')).rejects.toThrow('timeout');
   });

src/browser.ts

@@ -442,13 +442,13 @@ export class PlaywrightMCP {
         }));
       }, timeout * 1000);
 
-      const mcpArgs: string[] = [mcpPath, '--extension'];
+      const mcpArgs = buildMcpArgs({
+        mcpPath,
+        executablePath: process.env.OPENCLI_BROWSER_EXECUTABLE_PATH,
+      });
       if (process.env.OPENCLI_VERBOSE) {
         console.error(`[opencli] Extension token: ${extensionToken ? `configured (fingerprint ${tokenFingerprint})` : 'missing'}`);
       }
-      if (process.env.OPENCLI_BROWSER_EXECUTABLE_PATH) {
-        mcpArgs.push('--executablePath', process.env.OPENCLI_BROWSER_EXECUTABLE_PATH);
-      }
       debugLog(`Spawning node ${mcpArgs.join(' ')}`);
 
       this._proc = spawn('node', mcpArgs, {
@@ -664,6 +664,14 @@ function appendLimited(current: string, chunk: string, limit: number): string {
   return next.slice(-limit);
 }
 
+function buildMcpArgs(input: { mcpPath: string; executablePath?: string | null }): string[] {
+  const args = [input.mcpPath, '--extension'];
+  if (input.executablePath) {
+    args.push('--executable-path', input.executablePath);
+  }
+  return args;
+}
+
 function withTimeout<T>(promise: Promise<T>, timeoutMs: number, message: string): Promise<T> {
   return new Promise<T>((resolve, reject) => {
     const timer = setTimeout(() => reject(new Error(message)), timeoutMs);
@@ -685,6 +693,7 @@ export const __test__ = {
   extractTabEntries,
   diffTabIndexes,
   appendLimited,
+  buildMcpArgs,
   withTimeout,
 };