fix(tui): add composer_arrows_scroll config option for trackpad terminals

Instead of unconditionally changing Up/Down behavior, gate the
empty-composer-scroll path behind a new `tui.composer_arrows_scroll`
config option (default false).  Users whose terminals map trackpad
gestures to arrow keys can opt in via:

    [tui]
    composer_arrows_scroll = true

When enabled, empty-composer Up/Down scroll the transcript; otherwise
plain arrows always navigate input history (preserving #1117 default).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/tui/src/config.rs

@@ -388,6 +388,12 @@ pub struct TuiConfig {
     /// - `Never` — suppress all turn-completion notifications.
     /// - Unset (default) — fall back to the `[notifications]` defaults.
     pub notification_condition: Option<NotificationCondition>,
+    /// When `true`, plain Up/Down on an empty composer scroll the
+    /// transcript instead of recalling input history.  Useful for
+    /// terminals that map trackpad gestures to arrow keys.  Default:
+    /// `false` (plain arrows always navigate input history, #1117).
+    #[serde(default)]
+    pub composer_arrows_scroll: Option<bool>,
 }
 
 /// High-level notification trigger override. See

crates/tui/src/main.rs

@@ -4644,6 +4644,7 @@ mod terminal_mode_tests {
                 terminal_probe_timeout_ms: None,
                 status_items: None,
                 osc8_links: None,
+                composer_arrows_scroll: None,
                 notification_condition: None,
             }),
             ..Config::default()
@@ -4717,6 +4718,7 @@ mod terminal_mode_tests {
                 terminal_probe_timeout_ms: None,
                 status_items: None,
                 osc8_links: None,
+                composer_arrows_scroll: None,
                 notification_condition: None,
             }),
             ..Config::default()
@@ -4747,6 +4749,7 @@ mod terminal_mode_tests {
                 terminal_probe_timeout_ms: None,
                 status_items: None,
                 osc8_links: None,
+                composer_arrows_scroll: None,
                 notification_condition: None,
             }),
             ..Config::default()
@@ -4828,6 +4831,7 @@ mod terminal_mode_tests {
                 terminal_probe_timeout_ms: None,
                 status_items: None,
                 osc8_links: None,
+                composer_arrows_scroll: None,
                 notification_condition: None,
             }),
             ..Config::default()

crates/tui/src/tui/app.rs

@@ -720,6 +720,9 @@ pub struct App {
     pub use_memory: bool,
     pub use_alt_screen: bool,
     pub use_mouse_capture: bool,
+    /// When true, plain Up/Down on an empty composer scroll the transcript
+    /// instead of navigating input history (#1117 opt-in).
+    pub composer_arrows_scroll: bool,
     pub use_bracketed_paste: bool,
     pub use_paste_burst_detection: bool,
     #[allow(dead_code)]
@@ -1440,6 +1443,11 @@ impl App {
             collapsed_cell_map: Vec::new(),
             edit_in_progress: false,
             lsp_enabled: config.lsp.as_ref().and_then(|l| l.enabled).unwrap_or(true),
+            composer_arrows_scroll: config
+                .tui
+                .as_ref()
+                .and_then(|tui| tui.composer_arrows_scroll)
+                .unwrap_or(false),
         }
     }
 

crates/tui/src/tui/ui.rs

@@ -3591,13 +3591,27 @@ fn handle_composer_history_arrow(
         return false;
     }
 
+    // When `composer_arrows_scroll` is enabled and the composer is empty,
+    // plain Up/Down scroll the transcript.  This helps terminals that map
+    // trackpad gestures to arrow keys.  Otherwise arrows always navigate
+    // input history regardless of composer state (#1117).
+    let scroll_on_empty = app.composer_arrows_scroll && app.input.trim().is_empty();
+
     match key.code {
         KeyCode::Up => {
-            app.history_up();
+            if scroll_on_empty {
+                app.scroll_up(1);
+            } else {
+                app.history_up();
+            }
             true
         }
         KeyCode::Down => {
-            app.history_down();
+            if scroll_on_empty {
+                app.scroll_down(1);
+            } else {
+                app.history_down();
+            }
             true
         }
         _ => false,

crates/tui/src/tui/ui/tests.rs

@@ -1259,6 +1259,7 @@ fn terminal_probe_timeout_uses_tui_config_and_clamps() {
             status_items: None,
             osc8_links: None,
             notification_condition: None,
+            composer_arrows_scroll: None,
         }),
         ..Config::default()
     };
@@ -4385,13 +4386,13 @@ fn history_arrow_handles_empty_input() {
     let mut app = create_test_app();
     app.input_history.push("previous prompt".to_string());
 
+    // Default: empty composer Up navigates input history (#1117).
     assert!(handle_composer_history_arrow(
         &mut app,
         KeyEvent::new(KeyCode::Up, KeyModifiers::NONE),
         false,
         false,
     ));
-
     assert_eq!(app.input, "previous prompt");
 }
 
@@ -4408,7 +4409,6 @@ fn history_arrow_handles_whitespace_input() {
         false,
         false,
     ));
-
     assert_eq!(app.input, "previous prompt");
 }
 
@@ -4429,6 +4429,54 @@ fn history_arrow_handles_nonempty_input() {
     assert_eq!(app.input, "previous prompt");
 }
 
+#[test]
+fn composer_arrows_scroll_empty_up() {
+    let mut app = create_test_app();
+    app.composer_arrows_scroll = true;
+
+    // Opt-in: empty composer Up scrolls transcript.
+    assert!(handle_composer_history_arrow(
+        &mut app,
+        KeyEvent::new(KeyCode::Up, KeyModifiers::NONE),
+        false,
+        false,
+    ));
+    assert_eq!(app.viewport.pending_scroll_delta, -1);
+    assert!(app.input.is_empty());
+}
+
+#[test]
+fn composer_arrows_scroll_empty_down() {
+    let mut app = create_test_app();
+    app.composer_arrows_scroll = true;
+
+    assert!(handle_composer_history_arrow(
+        &mut app,
+        KeyEvent::new(KeyCode::Down, KeyModifiers::NONE),
+        false,
+        false,
+    ));
+    assert_eq!(app.viewport.pending_scroll_delta, 1);
+}
+
+#[test]
+fn composer_arrows_scroll_nonempty_still_navigates_history() {
+    let mut app = create_test_app();
+    app.composer_arrows_scroll = true;
+    app.input = "hello".to_string();
+    app.cursor_position = app.input.chars().count();
+    app.input_history.push("previous prompt".to_string());
+
+    // Even with the option on, non-empty composer still navigates history.
+    assert!(handle_composer_history_arrow(
+        &mut app,
+        KeyEvent::new(KeyCode::Up, KeyModifiers::NONE),
+        false,
+        false,
+    ));
+    assert_eq!(app.input, "previous prompt");
+}
+
 #[test]
 fn notification_settings_tui_always_keeps_configured_method_no_threshold() {
     let config = Config {