fix: discover global @playwright/mcp for nvm/npm installs (#42)

* fix: discover global @playwright/mcp in nvm/npm installs

* test: cover global mcp discovery paths

---------

Co-authored-by: jackwener <jakevingoo@gmail.com>

src/browser.test.ts

@@ -1,6 +1,12 @@
-import { describe, it, expect } from 'vitest';
+import { afterEach, describe, it, expect, vi } from 'vitest';
 import { PlaywrightMCP, __test__ } from './browser/index.js';
 
+afterEach(() => {
+  __test__.resetMcpServerPathCache();
+  __test__.setMcpDiscoveryTestHooks();
+  delete process.env.OPENCLI_MCP_SERVER_PATH;
+});
+
 describe('browser helpers', () => {
   it('creates JSON-RPC requests with unique ids', () => {
     const first = __test__.createJsonRpcRequest('tools/call', { name: 'browser_tabs' });
@@ -109,6 +115,98 @@ describe('browser helpers', () => {
   it('times out slow promises', async () => {
     await expect(__test__.withTimeoutMs(new Promise(() => {}), 10, 'timeout')).rejects.toThrow('timeout');
   });
+
+  it('prefers OPENCLI_MCP_SERVER_PATH over discovered locations', () => {
+    process.env.OPENCLI_MCP_SERVER_PATH = '/env/mcp/cli.js';
+    const existsSync = vi.fn((candidate: any) => candidate === '/env/mcp/cli.js');
+    const execSync = vi.fn();
+    __test__.setMcpDiscoveryTestHooks({ existsSync, execSync: execSync as any });
+
+    expect(__test__.findMcpServerPath()).toBe('/env/mcp/cli.js');
+    expect(execSync).not.toHaveBeenCalled();
+    expect(existsSync).toHaveBeenCalledWith('/env/mcp/cli.js');
+  });
+
+  it('discovers global @playwright/mcp from the current Node runtime prefix', () => {
+    const originalExecPath = process.execPath;
+    const runtimeExecPath = '/opt/homebrew/Cellar/node/25.2.1/bin/node';
+    const runtimeGlobalMcp = '/opt/homebrew/Cellar/node/25.2.1/lib/node_modules/@playwright/mcp/cli.js';
+    Object.defineProperty(process, 'execPath', {
+      value: runtimeExecPath,
+      configurable: true,
+    });
+
+    const existsSync = vi.fn((candidate: any) => candidate === runtimeGlobalMcp);
+    const execSync = vi.fn();
+    __test__.setMcpDiscoveryTestHooks({ existsSync, execSync: execSync as any });
+
+    try {
+      expect(__test__.findMcpServerPath()).toBe(runtimeGlobalMcp);
+      expect(execSync).not.toHaveBeenCalled();
+      expect(existsSync).toHaveBeenCalledWith(runtimeGlobalMcp);
+    } finally {
+      Object.defineProperty(process, 'execPath', {
+        value: originalExecPath,
+        configurable: true,
+      });
+    }
+  });
+
+  it('falls back to npm root -g when runtime prefix lookup misses', () => {
+    const originalExecPath = process.execPath;
+    const runtimeExecPath = '/opt/homebrew/Cellar/node/25.2.1/bin/node';
+    const runtimeGlobalMcp = '/opt/homebrew/Cellar/node/25.2.1/lib/node_modules/@playwright/mcp/cli.js';
+    const npmRootGlobal = '/Users/jakevin/.nvm/versions/node/v22.14.0/lib/node_modules';
+    const npmGlobalMcp = '/Users/jakevin/.nvm/versions/node/v22.14.0/lib/node_modules/@playwright/mcp/cli.js';
+    Object.defineProperty(process, 'execPath', {
+      value: runtimeExecPath,
+      configurable: true,
+    });
+
+    const existsSync = vi.fn((candidate: any) => candidate === npmGlobalMcp);
+    const execSync = vi.fn((command: string) => {
+      if (String(command).includes('npm root -g')) return `${npmRootGlobal}\n` as any;
+      throw new Error(`unexpected command: ${String(command)}`);
+    });
+    __test__.setMcpDiscoveryTestHooks({ existsSync, execSync: execSync as any });
+
+    try {
+      expect(__test__.findMcpServerPath()).toBe(npmGlobalMcp);
+      expect(execSync).toHaveBeenCalledOnce();
+      expect(existsSync).toHaveBeenCalledWith(runtimeGlobalMcp);
+      expect(existsSync).toHaveBeenCalledWith(npmGlobalMcp);
+    } finally {
+      Object.defineProperty(process, 'execPath', {
+        value: originalExecPath,
+        configurable: true,
+      });
+    }
+  });
+
+  it('returns null when new global discovery paths are unavailable', () => {
+    const originalExecPath = process.execPath;
+    const runtimeExecPath = '/opt/homebrew/Cellar/node/25.2.1/bin/node';
+    Object.defineProperty(process, 'execPath', {
+      value: runtimeExecPath,
+      configurable: true,
+    });
+
+    const existsSync = vi.fn(() => false);
+    const execSync = vi.fn((command: string) => {
+      if (String(command).includes('npm root -g')) return '/missing/global/node_modules\n' as any;
+      throw new Error(`missing command: ${String(command)}`);
+    });
+    __test__.setMcpDiscoveryTestHooks({ existsSync, execSync: execSync as any });
+
+    try {
+      expect(__test__.findMcpServerPath()).toBeNull();
+    } finally {
+      Object.defineProperty(process, 'execPath', {
+        value: originalExecPath,
+        configurable: true,
+      });
+    }
+  });
 });
 
 describe('PlaywrightMCP state', () => {

src/browser/discover.ts

@@ -9,19 +9,33 @@ import * as os from 'node:os';
 import * as path from 'node:path';
 
 let _cachedMcpServerPath: string | null | undefined;
+let _existsSync = fs.existsSync;
+let _execSync = execSync;
+
+export function resetMcpServerPathCache(): void {
+  _cachedMcpServerPath = undefined;
+}
+
+export function setMcpDiscoveryTestHooks(input?: {
+  existsSync?: typeof fs.existsSync;
+  execSync?: typeof execSync;
+}): void {
+  _existsSync = input?.existsSync ?? fs.existsSync;
+  _execSync = input?.execSync ?? execSync;
+}
 
 export function findMcpServerPath(): string | null {
   if (_cachedMcpServerPath !== undefined) return _cachedMcpServerPath;
 
   const envMcp = process.env.OPENCLI_MCP_SERVER_PATH;
-  if (envMcp && fs.existsSync(envMcp)) {
+  if (envMcp && _existsSync(envMcp)) {
     _cachedMcpServerPath = envMcp;
     return _cachedMcpServerPath;
   }
 
   // Check local node_modules first (@playwright/mcp is the modern package)
   const localMcp = path.resolve('node_modules', '@playwright', 'mcp', 'cli.js');
-  if (fs.existsSync(localMcp)) {
+  if (_existsSync(localMcp)) {
     _cachedMcpServerPath = localMcp;
     return _cachedMcpServerPath;
   }
@@ -29,11 +43,33 @@ export function findMcpServerPath(): string | null {
   // Check project-relative path
   const __dirname2 = path.dirname(fileURLToPath(import.meta.url));
   const projectMcp = path.resolve(__dirname2, '..', '..', 'node_modules', '@playwright', 'mcp', 'cli.js');
-  if (fs.existsSync(projectMcp)) {
+  if (_existsSync(projectMcp)) {
     _cachedMcpServerPath = projectMcp;
     return _cachedMcpServerPath;
   }
 
+  // Check global npm/yarn locations derived from current Node runtime.
+  const nodePrefix = path.resolve(path.dirname(process.execPath), '..');
+  const globalNodeModules = path.join(nodePrefix, 'lib', 'node_modules');
+  const globalMcp = path.join(globalNodeModules, '@playwright', 'mcp', 'cli.js');
+  if (_existsSync(globalMcp)) {
+    _cachedMcpServerPath = globalMcp;
+    return _cachedMcpServerPath;
+  }
+
+  // Check npm global root directly.
+  try {
+    const npmRootGlobal = _execSync('npm root -g 2>/dev/null', {
+      encoding: 'utf-8',
+      timeout: 5000,
+    }).trim();
+    const npmGlobalMcp = path.join(npmRootGlobal, '@playwright', 'mcp', 'cli.js');
+    if (npmRootGlobal && _existsSync(npmGlobalMcp)) {
+      _cachedMcpServerPath = npmGlobalMcp;
+      return _cachedMcpServerPath;
+    }
+  } catch {}
+
   // Check common locations
   const candidates = [
     path.join(os.homedir(), '.npm', '_npx'),
@@ -43,8 +79,8 @@ export function findMcpServerPath(): string | null {
 
   // Try npx resolution (legacy package name)
   try {
-    const result = execSync('npx -y --package=@playwright/mcp which mcp-server-playwright 2>/dev/null', { encoding: 'utf-8', timeout: 10000 }).trim();
-    if (result && fs.existsSync(result)) {
+    const result = _execSync('npx -y --package=@playwright/mcp which mcp-server-playwright 2>/dev/null', { encoding: 'utf-8', timeout: 10000 }).trim();
+    if (result && _existsSync(result)) {
       _cachedMcpServerPath = result;
       return _cachedMcpServerPath;
     }
@@ -52,8 +88,8 @@ export function findMcpServerPath(): string | null {
 
   // Try which
   try {
-    const result = execSync('which mcp-server-playwright 2>/dev/null', { encoding: 'utf-8', timeout: 5000 }).trim();
-    if (result && fs.existsSync(result)) {
+    const result = _execSync('which mcp-server-playwright 2>/dev/null', { encoding: 'utf-8', timeout: 5000 }).trim();
+    if (result && _existsSync(result)) {
       _cachedMcpServerPath = result;
       return _cachedMcpServerPath;
     }
@@ -61,9 +97,9 @@ export function findMcpServerPath(): string | null {
 
   // Search in common npx cache
   for (const base of candidates) {
-    if (!fs.existsSync(base)) continue;
+    if (!_existsSync(base)) continue;
     try {
-      const found = execSync(`find "${base}" -name "cli.js" -path "*playwright*mcp*" 2>/dev/null | head -1`, { encoding: 'utf-8', timeout: 5000 }).trim();
+      const found = _execSync(`find "${base}" -name "cli.js" -path "*playwright*mcp*" 2>/dev/null | head -1`, { encoding: 'utf-8', timeout: 5000 }).trim();
       if (found) {
         _cachedMcpServerPath = found;
         return _cachedMcpServerPath;

src/browser/index.ts

@@ -13,7 +13,7 @@ export type { ConnectFailureKind, ConnectFailureInput } from './errors.js';
 // Test-only helpers — exposed for unit tests
 import { createJsonRpcRequest } from './mcp.js';
 import { extractTabEntries, diffTabIndexes, appendLimited } from './tabs.js';
-import { buildMcpArgs } from './discover.js';
+import { buildMcpArgs, findMcpServerPath, resetMcpServerPathCache, setMcpDiscoveryTestHooks } from './discover.js';
 import { withTimeoutMs } from '../runtime.js';
 
 export const __test__ = {
@@ -22,5 +22,8 @@ export const __test__ = {
   diffTabIndexes,
   appendLimited,
   buildMcpArgs,
+  findMcpServerPath,
+  resetMcpServerPathCache,
+  setMcpDiscoveryTestHooks,
   withTimeoutMs,
 };