feat(cli): support Ctrl-Z suspension

- Implement Ctrl+Z suspension with robust terminal state handling.
- Rebind Undo/Redo to Alt+Z / Alt+Shift+Z to avoid conflicts.
- Fix macOS Option key character mapping for Undo/Redo.
- Improve type safety for app.rerender() in AppContainer.
- Add comprehensive suspension test suite.
- Fix environment leakage in core tests.
- Update keyboard shortcut documentation.

Fixes google-gemini#5018

Author: brtkwr

docs/cli/keyboard-shortcuts.md

@@ -39,8 +39,8 @@ available combinations.
 | Delete the next word.                            | `Ctrl + Delete`<br />`Alt + Delete`                       |
 | Delete the character to the left.                | `Backspace`<br />`Ctrl + H`                               |
 | Delete the character to the right.               | `Delete`<br />`Ctrl + D`                                  |
-| Undo the most recent text edit.                  | `Ctrl + Z (no Shift)`                                     |
-| Redo the most recent undone text edit.           | `Shift + Ctrl + Z`                                        |
+| Undo the most recent text edit.                  | `Alt + Z (no Shift)`                                      |
+| Redo the most recent undone text edit.           | `Shift + Alt + Z`                                         |
 
 #### Scrolling
 
@@ -108,6 +108,7 @@ available combinations.
 | Focus the Gemini input from the shell input.                                                          | `Tab`                      |
 | Clear the terminal screen and redraw the UI.                                                          | `Ctrl + L`                 |
 | Restart the application.                                                                              | `R`                        |
+| Suspend the CLI and move it to the background.                                                        | `Ctrl + Z`                 |
 
 <!-- KEYBINDINGS-AUTOGEN:END -->
 

packages/cli/src/config/keyBindings.ts

@@ -83,6 +83,7 @@ export enum Command {
   UNFOCUS_SHELL_INPUT = 'app.unfocusShellInput',
   CLEAR_SCREEN = 'app.clearScreen',
   RESTART_APP = 'app.restart',
+  SUSPEND = 'app.suspend',
 }
 
 /**
@@ -168,8 +169,8 @@ export const defaultKeyBindings: KeyBindingConfig = {
   ],
   [Command.DELETE_CHAR_LEFT]: [{ key: 'backspace' }, { key: 'h', ctrl: true }],
   [Command.DELETE_CHAR_RIGHT]: [{ key: 'delete' }, { key: 'd', ctrl: true }],
-  [Command.UNDO]: [{ key: 'z', shift: false, ctrl: true }],
-  [Command.REDO]: [{ key: 'z', shift: true, ctrl: true }],
+  [Command.UNDO]: [{ key: 'z', alt: true, shift: false }],
+  [Command.REDO]: [{ key: 'z', alt: true, shift: true }],
 
   // Scrolling
   [Command.SCROLL_UP]: [{ key: 'up', shift: true }],
@@ -253,6 +254,7 @@ export const defaultKeyBindings: KeyBindingConfig = {
   [Command.TOGGLE_COPY_MODE]: [{ key: 's', ctrl: true }],
   [Command.TOGGLE_YOLO]: [{ key: 'y', ctrl: true }],
   [Command.CYCLE_APPROVAL_MODE]: [{ key: 'tab', shift: true }],
+  [Command.SUSPEND]: [{ key: 'z', ctrl: true }],
   [Command.SHOW_MORE_LINES]: [
     { key: 'o', ctrl: true },
     { key: 's', ctrl: true },
@@ -368,6 +370,7 @@ export const commandCategories: readonly CommandCategory[] = [
       Command.UNFOCUS_SHELL_INPUT,
       Command.CLEAR_SCREEN,
       Command.RESTART_APP,
+      Command.SUSPEND,
     ],
   },
 ];
@@ -450,6 +453,7 @@ export const commandDescriptions: Readonly<Record<Command, string>> = {
   [Command.TOGGLE_YOLO]: 'Toggle YOLO (auto-approval) mode for tool calls.',
   [Command.CYCLE_APPROVAL_MODE]:
     'Cycle through approval modes: default (prompt), auto_edit (auto-approve edits), and plan (read-only).',
+  [Command.SUSPEND]: 'Suspend the CLI and move it to the background.',
   [Command.SHOW_MORE_LINES]:
     'Expand a height-constrained response to show additional lines when not in alternate buffer mode.',
   [Command.FOCUS_SHELL_INPUT]: 'Focus the shell input from the gemini input.',