alternate buffer support (#12471)

docs/cli/keyboard-shortcuts.md

@@ -11,6 +11,7 @@ This document lists the available keyboard shortcuts within Gemini CLI.
 | `Ctrl+D`    | Exit the application if the input is empty. Press twice to confirm.                                                   |
 | `Ctrl+L`    | Clear the screen.                                                                                                     |
 | `Ctrl+S`    | Allows long responses to print fully, disabling truncation. Use your terminal's scrollback to view the entire output. |
+| `Ctrl+S`    | Toggle copy mode (alternate buffer mode only).                                                                        |
 | `Ctrl+T`    | Toggle the display of the todo list.                                                                                  |
 | `Ctrl+Y`    | Toggle auto-approval (YOLO mode) for all tool calls.                                                                  |
 | `Shift+Tab` | Toggle auto-accepting edits approval mode.                                                                            |

docs/get-started/configuration.md

@@ -229,6 +229,12 @@ their corresponding top-level category object in your `settings.json` file.
   - **Description:** Use the entire width of the terminal for output.
   - **Default:** `false`
 
+- **`ui.useAlternateBuffer`** (boolean):
+  - **Description:** Use an alternate screen buffer for the UI, preserving shell
+    history.
+  - **Default:** `false`
+  - **Requires restart:** Yes
+
 - **`ui.customWittyPhrases`** (array):
   - **Description:** Custom witty phrases to display during loading. When
     provided, the CLI cycles through these instead of the defaults.