fix(mcp): add missing .catch() on sessionLog write queue (#41234)

`SessionLog._sessionFileQueue` chains `appendFile` calls with no `.catch()`.

If a single write rejects (disk full, permissions), the chain stays permanently rejected and all future log entries are silently dropped for the rest of the MCP session.

Add `.catch(e => debug('pw:tools:error')(e))` to match the pattern in `logFile.ts:55`.

This was first introduced in <https://github.com/microsoft/playwright/commit/90e302ba39cf04812054fcd80f633a913dceb46e> (<https://github.com/microsoft/playwright/pull/37286>, 2025-09-03).

packages/playwright-core/src/tools/backend/sessionLog.ts

@@ -17,6 +17,8 @@
 import fs from 'fs';
 import path from 'path';
 
+import debug from 'debug';
+
 import { outputFile  } from './context';
 import { parseResponse } from './response';
 
@@ -60,6 +62,6 @@ export class SessionLog {
     }
 
     lines.push('');
-    this._sessionFileQueue = this._sessionFileQueue.then(() => fs.promises.appendFile(this._file, lines.join('\n')));
+    this._sessionFileQueue = this._sessionFileQueue.then(() => fs.promises.appendFile(this._file, lines.join('\n'))).catch(e => debug('pw:tools:error')(e));
   }
 }

tests/mcp/session-log.spec.ts

@@ -84,6 +84,53 @@ test('session log should record tool calls', async ({ startClient, server, mcpBr
 `.trim()));
 });
 
+test('session log should recover after write failure', async ({ startClient, server, mcpBrowser }, testInfo) => {
+  test.skip(mcpBrowser === 'webkit');
+
+  const { client, stderr } = await startClient({
+    args: [
+      '--save-session',
+      '--output-dir', testInfo.outputPath('output'),
+    ],
+  });
+
+  server.setContent('/', `<title>Title</title><button>Submit</button>`, 'text/html');
+
+  // First call: logs successfully.
+  await client.callTool({
+    name: 'browser_navigate',
+    arguments: { url: server.PREFIX },
+  });
+
+  const output = stderr().split('\n').filter(line => line.startsWith('Session: '))[0];
+  const sessionFolder = output.substring('Session: '.length);
+  const sessionFile = path.join(sessionFolder, 'session.md');
+
+  // Wait for the first entry to be written.
+  await expect.poll(() => readSessionLog(sessionFolder)).toContain('browser_navigate');
+
+  // Make the session file read-only so the next write fails.
+  await fs.promises.chmod(sessionFile, 0o444);
+
+  // Second call: write fails (EACCES) but the chain should recover.
+  await client.callTool({
+    name: 'browser_click',
+    arguments: { element: 'Submit button', target: 'e2' },
+  });
+
+  // Restore write permission.
+  await fs.promises.chmod(sessionFile, 0o644);
+
+  // Third call: without the fix the chain stays rejected and this is never logged.
+  await client.callTool({
+    name: 'browser_click',
+    arguments: { element: 'Submit button', target: 'e2' },
+  });
+
+  // Verify the third call was logged (chain recovered).
+  await expect.poll(() => readSessionLog(sessionFolder)).toContain('browser_click');
+});
+
 async function readSessionLog(sessionFolder: string): Promise<string> {
   return await fs.promises.readFile(path.join(sessionFolder, 'session.md'), 'utf8').catch(() => '');
 }