From 78130d4bb70a8f55cb5953f4d7b49584f63d783a Mon Sep 17 00:00:00 2001
From: Srinath Padmanabhan <17151014+srithreepo@users.noreply.github.com>
Date: Sat, 14 Feb 2026 20:08:13 -0800
Subject: [PATCH] fix(cli): wrap terminal capability queries in hidden sequence
 (#19080)

Co-authored-by: Srinath Padmanabhan <srithreepo@google.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
---
 .../ui/utils/terminalCapabilityManager.test.ts    | 12 ++++++++++++
 .../cli/src/ui/utils/terminalCapabilityManager.ts | 15 +++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/packages/cli/src/ui/utils/terminalCapabilityManager.test.ts b/packages/cli/src/ui/utils/terminalCapabilityManager.test.ts
index fce18cfb01..846fe2d8cb 100644
--- a/packages/cli/src/ui/utils/terminalCapabilityManager.test.ts
+++ b/packages/cli/src/ui/utils/terminalCapabilityManager.test.ts
@@ -11,6 +11,7 @@ import {
   enableKittyKeyboardProtocol,
   enableModifyOtherKeys,
 } from '@google/gemini-cli-core';
+import * as fs from 'node:fs';
 
 // Mock fs
 vi.mock('node:fs', () => ({
@@ -289,5 +290,16 @@ describe('TerminalCapabilityManager', () => {
       expect(manager.isKittyProtocolEnabled()).toBe(false);
       expect(enableModifyOtherKeys).not.toHaveBeenCalled();
     });
+
+    it('should wrap queries in hidden/clear sequence', async () => {
+      const manager = TerminalCapabilityManager.getInstance();
+      void manager.detectCapabilities();
+
+      expect(fs.writeSync).toHaveBeenCalledWith(
+        expect.anything(),
+        // eslint-disable-next-line no-control-regex
+        expect.stringMatching(/^\x1b\[8m.*\x1b\[2K\r\x1b\[0m$/s),
+      );
+    });
   });
 });
diff --git a/packages/cli/src/ui/utils/terminalCapabilityManager.ts b/packages/cli/src/ui/utils/terminalCapabilityManager.ts
index 447c79ce91..76de5b831e 100644
--- a/packages/cli/src/ui/utils/terminalCapabilityManager.ts
+++ b/packages/cli/src/ui/utils/terminalCapabilityManager.ts
@@ -43,6 +43,9 @@ export class TerminalCapabilityManager {
   private static readonly TERMINAL_NAME_QUERY = '\x1b[>q';
   private static readonly DEVICE_ATTRIBUTES_QUERY = '\x1b[c';
   private static readonly MODIFY_OTHER_KEYS_QUERY = '\x1b[>4;?m';
+  private static readonly HIDDEN_MODE = '\x1b[8m';
+  private static readonly CLEAR_LINE_AND_RETURN = '\x1b[2K\r';
+  private static readonly RESET_ATTRIBUTES = '\x1b[0m';
 
   /**
    * Triggers a terminal background color query.
@@ -219,11 +222,19 @@ export class TerminalCapabilityManager {
       try {
         fs.writeSync(
           process.stdout.fd,
-          TerminalCapabilityManager.KITTY_QUERY +
+          // Use hidden mode to prevent potential "m" character from being printed
+          // to the terminal during startup when querying for modifyOtherKeys.
+          // This can happen on some terminals that might echo the query or
+          // malform the response. We hide the output, send queries, then
+          // immediately clear the line and reset attributes.
+          TerminalCapabilityManager.HIDDEN_MODE +
+            TerminalCapabilityManager.KITTY_QUERY +
             TerminalCapabilityManager.OSC_11_QUERY +
             TerminalCapabilityManager.TERMINAL_NAME_QUERY +
             TerminalCapabilityManager.MODIFY_OTHER_KEYS_QUERY +
-            TerminalCapabilityManager.DEVICE_ATTRIBUTES_QUERY,
+            TerminalCapabilityManager.DEVICE_ATTRIBUTES_QUERY +
+            TerminalCapabilityManager.CLEAR_LINE_AND_RETURN +
+            TerminalCapabilityManager.RESET_ATTRIBUTES,
         );
       } catch (e) {
         debugLogger.warn('Failed to write terminal capability queries:', e);