feat(cli): support Ctrl-Z suspension (#18931)

Co-authored-by: Bharat Kunwar <brtkwr@gmail.com>

packages/cli/src/ui/hooks/useSuspend.test.ts

@@ -0,0 +1,201 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  afterEach,
+  type Mock,
+} from 'vitest';
+import { act } from 'react';
+import { renderHook } from '../../test-utils/render.js';
+import { useSuspend } from './useSuspend.js';
+import {
+  writeToStdout,
+  disableMouseEvents,
+  enableMouseEvents,
+  enterAlternateScreen,
+  exitAlternateScreen,
+  enableLineWrapping,
+  disableLineWrapping,
+} from '@google/gemini-cli-core';
+import {
+  cleanupTerminalOnExit,
+  terminalCapabilityManager,
+} from '../utils/terminalCapabilityManager.js';
+
+vi.mock('@google/gemini-cli-core', async () => {
+  const actual = await vi.importActual('@google/gemini-cli-core');
+  return {
+    ...actual,
+    writeToStdout: vi.fn(),
+    disableMouseEvents: vi.fn(),
+    enableMouseEvents: vi.fn(),
+    enterAlternateScreen: vi.fn(),
+    exitAlternateScreen: vi.fn(),
+    enableLineWrapping: vi.fn(),
+    disableLineWrapping: vi.fn(),
+  };
+});
+
+vi.mock('../utils/terminalCapabilityManager.js', () => ({
+  cleanupTerminalOnExit: vi.fn(),
+  terminalCapabilityManager: {
+    enableSupportedModes: vi.fn(),
+  },
+}));
+
+describe('useSuspend', () => {
+  const originalPlatform = process.platform;
+  let killSpy: Mock;
+
+  const setPlatform = (platform: NodeJS.Platform) => {
+    Object.defineProperty(process, 'platform', {
+      value: platform,
+      configurable: true,
+    });
+  };
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.clearAllMocks();
+    killSpy = vi
+      .spyOn(process, 'kill')
+      .mockReturnValue(true) as unknown as Mock;
+    // Default tests to a POSIX platform so suspend path assertions are stable.
+    setPlatform('linux');
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    killSpy.mockRestore();
+    setPlatform(originalPlatform);
+  });
+
+  it('cleans terminal state on suspend and restores/repaints on resume in alternate screen mode', () => {
+    const handleWarning = vi.fn();
+    const setRawMode = vi.fn();
+    const refreshStatic = vi.fn();
+    const setForceRerenderKey = vi.fn();
+    const enableSupportedModes =
+      terminalCapabilityManager.enableSupportedModes as unknown as Mock;
+
+    const { result, unmount } = renderHook(() =>
+      useSuspend({
+        handleWarning,
+        setRawMode,
+        refreshStatic,
+        setForceRerenderKey,
+        shouldUseAlternateScreen: true,
+      }),
+    );
+
+    act(() => {
+      result.current.handleSuspend();
+    });
+    expect(handleWarning).toHaveBeenCalledWith(
+      'Press Ctrl+Z again to suspend. Undo has moved to Cmd + Z or Alt/Opt + Z.',
+    );
+
+    act(() => {
+      result.current.handleSuspend();
+    });
+
+    expect(exitAlternateScreen).toHaveBeenCalledTimes(1);
+    expect(enableLineWrapping).toHaveBeenCalledTimes(1);
+    expect(writeToStdout).toHaveBeenCalledWith('\x1b[2J\x1b[H');
+    expect(disableMouseEvents).toHaveBeenCalledTimes(1);
+    expect(cleanupTerminalOnExit).toHaveBeenCalledTimes(1);
+    expect(setRawMode).toHaveBeenCalledWith(false);
+    expect(killSpy).toHaveBeenCalledWith(0, 'SIGTSTP');
+
+    act(() => {
+      process.emit('SIGCONT');
+      vi.runAllTimers();
+    });
+
+    expect(enterAlternateScreen).toHaveBeenCalledTimes(1);
+    expect(disableLineWrapping).toHaveBeenCalledTimes(1);
+    expect(enableSupportedModes).toHaveBeenCalledTimes(1);
+    expect(enableMouseEvents).toHaveBeenCalledTimes(1);
+    expect(setRawMode).toHaveBeenCalledWith(true);
+    expect(refreshStatic).toHaveBeenCalledTimes(1);
+    expect(setForceRerenderKey).toHaveBeenCalledTimes(1);
+
+    unmount();
+  });
+
+  it('does not toggle alternate screen or mouse restore when alternate screen mode is disabled', () => {
+    const handleWarning = vi.fn();
+    const setRawMode = vi.fn();
+    const refreshStatic = vi.fn();
+    const setForceRerenderKey = vi.fn();
+
+    const { result, unmount } = renderHook(() =>
+      useSuspend({
+        handleWarning,
+        setRawMode,
+        refreshStatic,
+        setForceRerenderKey,
+        shouldUseAlternateScreen: false,
+      }),
+    );
+
+    act(() => {
+      result.current.handleSuspend();
+      result.current.handleSuspend();
+      process.emit('SIGCONT');
+      vi.runAllTimers();
+    });
+
+    expect(exitAlternateScreen).not.toHaveBeenCalled();
+    expect(enterAlternateScreen).not.toHaveBeenCalled();
+    expect(enableLineWrapping).not.toHaveBeenCalled();
+    expect(disableLineWrapping).not.toHaveBeenCalled();
+    expect(enableMouseEvents).not.toHaveBeenCalled();
+
+    unmount();
+  });
+
+  it('warns and skips suspension on windows', () => {
+    setPlatform('win32');
+
+    const handleWarning = vi.fn();
+    const setRawMode = vi.fn();
+    const refreshStatic = vi.fn();
+    const setForceRerenderKey = vi.fn();
+
+    const { result, unmount } = renderHook(() =>
+      useSuspend({
+        handleWarning,
+        setRawMode,
+        refreshStatic,
+        setForceRerenderKey,
+        shouldUseAlternateScreen: true,
+      }),
+    );
+
+    act(() => {
+      result.current.handleSuspend();
+    });
+    handleWarning.mockClear();
+
+    act(() => {
+      result.current.handleSuspend();
+    });
+
+    expect(handleWarning).toHaveBeenCalledWith(
+      'Ctrl+Z suspend is not supported on Windows.',
+    );
+    expect(killSpy).not.toHaveBeenCalled();
+    expect(cleanupTerminalOnExit).not.toHaveBeenCalled();
+
+    unmount();
+  });
+});

packages/cli/src/ui/hooks/useSuspend.ts

@@ -0,0 +1,155 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useState, useRef, useEffect, useCallback } from 'react';
+import {
+  writeToStdout,
+  disableMouseEvents,
+  enableMouseEvents,
+  enterAlternateScreen,
+  exitAlternateScreen,
+  enableLineWrapping,
+  disableLineWrapping,
+} from '@google/gemini-cli-core';
+import process from 'node:process';
+import {
+  cleanupTerminalOnExit,
+  terminalCapabilityManager,
+} from '../utils/terminalCapabilityManager.js';
+import { WARNING_PROMPT_DURATION_MS } from '../constants.js';
+
+interface UseSuspendProps {
+  handleWarning: (message: string) => void;
+  setRawMode: (mode: boolean) => void;
+  refreshStatic: () => void;
+  setForceRerenderKey: (updater: (prev: number) => number) => void;
+  shouldUseAlternateScreen: boolean;
+}
+
+export function useSuspend({
+  handleWarning,
+  setRawMode,
+  refreshStatic,
+  setForceRerenderKey,
+  shouldUseAlternateScreen,
+}: UseSuspendProps) {
+  const [ctrlZPressCount, setCtrlZPressCount] = useState(0);
+  const ctrlZTimerRef = useRef<NodeJS.Timeout | null>(null);
+  const onResumeHandlerRef = useRef<(() => void) | null>(null);
+
+  useEffect(
+    () => () => {
+      if (ctrlZTimerRef.current) {
+        clearTimeout(ctrlZTimerRef.current);
+        ctrlZTimerRef.current = null;
+      }
+      if (onResumeHandlerRef.current) {
+        process.off('SIGCONT', onResumeHandlerRef.current);
+        onResumeHandlerRef.current = null;
+      }
+    },
+    [],
+  );
+
+  useEffect(() => {
+    if (ctrlZTimerRef.current) {
+      clearTimeout(ctrlZTimerRef.current);
+      ctrlZTimerRef.current = null;
+    }
+    if (ctrlZPressCount > 1) {
+      setCtrlZPressCount(0);
+      if (process.platform === 'win32') {
+        handleWarning('Ctrl+Z suspend is not supported on Windows.');
+        return;
+      }
+
+      if (shouldUseAlternateScreen) {
+        // Leave alternate buffer before suspension so the shell stays usable.
+        exitAlternateScreen();
+        enableLineWrapping();
+        writeToStdout('\x1b[2J\x1b[H');
+      }
+
+      // Cleanup before suspend.
+      writeToStdout('\x1b[?25h'); // Show cursor
+      disableMouseEvents();
+      cleanupTerminalOnExit();
+
+      if (process.stdin.isTTY) {
+        process.stdin.setRawMode(false);
+      }
+      setRawMode(false);
+
+      const onResume = () => {
+        try {
+          // Restore terminal state.
+          if (process.stdin.isTTY) {
+            process.stdin.setRawMode(true);
+            process.stdin.resume();
+            process.stdin.ref();
+          }
+          setRawMode(true);
+
+          if (shouldUseAlternateScreen) {
+            enterAlternateScreen();
+            disableLineWrapping();
+            writeToStdout('\x1b[2J\x1b[H');
+          }
+
+          terminalCapabilityManager.enableSupportedModes();
+          writeToStdout('\x1b[?25l'); // Hide cursor
+          if (shouldUseAlternateScreen) {
+            enableMouseEvents();
+          }
+
+          // Force Ink to do a complete repaint by:
+          // 1. Emitting a resize event (tricks Ink into full redraw)
+          // 2. Remounting components via state changes
+          process.stdout.emit('resize');
+
+          // Give a tick for resize to process, then trigger remount
+          setImmediate(() => {
+            refreshStatic();
+            setForceRerenderKey((prev) => prev + 1);
+          });
+        } finally {
+          if (onResumeHandlerRef.current === onResume) {
+            onResumeHandlerRef.current = null;
+          }
+        }
+      };
+
+      if (onResumeHandlerRef.current) {
+        process.off('SIGCONT', onResumeHandlerRef.current);
+      }
+      onResumeHandlerRef.current = onResume;
+      process.once('SIGCONT', onResume);
+
+      process.kill(0, 'SIGTSTP');
+    } else if (ctrlZPressCount > 0) {
+      handleWarning(
+        'Press Ctrl+Z again to suspend. Undo has moved to Cmd + Z or Alt/Opt + Z.',
+      );
+      ctrlZTimerRef.current = setTimeout(() => {
+        setCtrlZPressCount(0);
+        ctrlZTimerRef.current = null;
+      }, WARNING_PROMPT_DURATION_MS);
+    }
+  }, [
+    ctrlZPressCount,
+    handleWarning,
+    setRawMode,
+    refreshStatic,
+    setForceRerenderKey,
+    shouldUseAlternateScreen,
+  ]);
+
+  const handleSuspend = useCallback(() => {
+    setCtrlZPressCount((prev) => prev + 1);
+  }, []);
+
+  return { handleSuspend };
+}