fix: kill Chrome process on MCP server shutdown to prevent orphaned processes

Chrome (headless) was launched but never cleaned up when the MCP client
disconnected or the server process was terminated. This caused orphaned
Chrome processes to accumulate across containers (59 found on np23.dev,
oldest 65+ hours, consuming >100% CPU combined).

Added graceful shutdown that kills the Chrome process on:
- SIGTERM/SIGINT/SIGHUP signals (container stop, Ctrl+C)
- MCP client disconnect (server.onclose)
- stdin close (parent process death)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Nima21

src/browser.ts

@@ -25,6 +25,35 @@ puppeteerExtra.use(StealthPlugin());
 
 let browser: Browser | undefined;
 
+/**
+ * Close the browser instance, killing the Chrome process if we launched it.
+ * Safe to call multiple times or when no browser exists.
+ */
+export async function closeBrowser(): Promise<void> {
+  if (!browser) {
+    return;
+  }
+  const b = browser;
+  browser = undefined;
+  try {
+    if (b.connected) {
+      // browser.close() sends a Browser.close CDP command and kills the process
+      // if it was launched by puppeteer. For connected browsers it just disconnects.
+      await b.close();
+    }
+  } catch {
+    // Best-effort: if close fails, try to kill the process directly
+    try {
+      const proc = b.process();
+      if (proc && !proc.killed) {
+        proc.kill('SIGKILL');
+      }
+    } catch {
+      // Nothing more we can do
+    }
+  }
+}
+
 function makeTargetFilter() {
   const ignoredPrefixes = new Set([
     'chrome://',

src/main.ts

@@ -9,7 +9,7 @@ import './polyfill.js';
 import process from 'node:process';
 
 import type {Channel} from './browser.js';
-import {ensureBrowserConnected, ensureBrowserLaunched} from './browser.js';
+import {closeBrowser, ensureBrowserConnected, ensureBrowserLaunched} from './browser.js';
 import {cliOptions, parseArguments} from './cli.js';
 import {loadIssueDescriptions} from './issue-descriptions.js';
 import {logger, saveLogsToFile} from './logger.js';
@@ -262,6 +262,46 @@ await loadIssueDescriptions();
 const transport = new StdioServerTransport();
 await server.connect(transport);
 logger('Chrome DevTools MCP Server connected');
+
+// Graceful shutdown: kill Chrome when the MCP server exits for any reason.
+let shuttingDown = false;
+async function gracefulShutdown(reason: string) {
+  if (shuttingDown) {
+    return;
+  }
+  shuttingDown = true;
+  logger(`Shutting down: ${reason}`);
+  try {
+    context?.dispose();
+  } catch {
+    // best-effort
+  }
+  try {
+    await closeBrowser();
+  } catch {
+    // best-effort
+  }
+  logger('Shutdown complete');
+  process.exit(0);
+}
+
+// Handle OS signals (container stop, systemd, Ctrl+C)
+for (const signal of ['SIGTERM', 'SIGINT', 'SIGHUP'] as const) {
+  process.on(signal, () => {
+    void gracefulShutdown(`received ${signal}`);
+  });
+}
+
+// Handle MCP client disconnect (transport/server close)
+server.server.onclose = () => {
+  void gracefulShutdown('MCP client disconnected');
+};
+
+// Handle stdin closing (parent process died)
+process.stdin.on('close', () => {
+  void gracefulShutdown('stdin closed');
+});
+
 logDisclaimers();
 void clearcutLogger?.logDailyActiveIfNeeded();
 void clearcutLogger?.logServerStart(computeFlagUsage(args, cliOptions));