fix: destroy both stdin and stdout on shutdown, guard against duplicate signals

- Close stdout in addition to stdin to prevent hanging writes during shutdown
- Add shuttingDown guard to ensure cleanup runs only once

Made-with: Cursor

packages/cli/src/acp-integration/acpAgent.ts

@@ -91,13 +91,21 @@ export async function runAcpAgent(
   // Without this, signal handlers registered elsewhere in the CLI
   // (e.g., stdin raw mode restoration) override the default exit behavior,
   // causing the ACP process to ignore termination signals.
+  let shuttingDown = false;
   const shutdownHandler = () => {
+    if (shuttingDown) return;
+    shuttingDown = true;
     debugLogger.debug('[ACP] Shutdown signal received, closing streams');
     try {
       process.stdin.destroy();
     } catch {
       // stdin may already be closed
     }
+    try {
+      process.stdout.destroy();
+    } catch {
+      // stdout may already be closed
+    }
   };
   process.on('SIGTERM', shutdownHandler);
   process.on('SIGINT', shutdownHandler);