슬래시 입력 UX 보강: 포커스/키 처리 통합 및 휠 fallback 추가

- InputBox_PreviewKeyDown에서 슬래시 네비게이션 키를 우선 처리

- TryHandleSlashNavigationKey로 창/입력창 키 경로 통합(Up/Down/Pg/Home/End/Tab/Enter/Esc)

- 가시 항목 0일 때 SlashScrollViewer 오프셋 fallback 추가

- README/DEVELOPMENT 이력(2026-04-04 16:18 KST) 동기화

src/AxCopilot/Views/ChatWindow.xaml.cs

@@ -4923,6 +4923,9 @@ public partial class ChatWindow : Window
 
     private async void InputBox_PreviewKeyDown(object sender, KeyEventArgs e)
     {
+        if (TryHandleSlashNavigationKey(e))
+            return;
+
         // Ctrl+V: 클립보드 이미지 붙여넣기
         if (e.Key == Key.V && Keyboard.Modifiers.HasFlag(ModifierKeys.Control))
         {
@@ -5571,6 +5574,13 @@ public partial class ChatWindow : Window
         if (_slashPalette.Matches.Count == 0)
             return;
 
+        if (GetVisibleSlashOrderedIndices().Count == 0)
+        {
+            if (SlashScrollViewer != null)
+                SlashScrollViewer.ScrollToVerticalOffset(Math.Max(0, SlashScrollViewer.VerticalOffset - delta / 3.0));
+            return;
+        }
+
         var steps = Math.Max(1, Math.Abs(delta) / 120);
         var direction = delta > 0 ? -1 : 1;
         for (var i = 0; i < steps; i++)
@@ -10902,61 +10912,69 @@ public partial class ChatWindow : Window
         }
 
         // 슬래시 명령 팝업 키 처리
-        if (SlashPopup.IsOpen)
+        if (TryHandleSlashNavigationKey(e))
+            return;
+
+        if (PermissionPopup.IsOpen && e.Key == Key.Escape)
         {
-            if (e.Key == Key.Escape)
-            {
+            PermissionPopup.IsOpen = false;
+            e.Handled = true;
+        }
+    }
+
+    private bool TryHandleSlashNavigationKey(KeyEventArgs e)
+    {
+        if (!SlashPopup.IsOpen)
+            return false;
+
+        switch (e.Key)
+        {
+            case Key.Escape:
                 SlashPopup.IsOpen = false;
                 _slashPalette.SelectedIndex = -1;
                 e.Handled = true;
-            }
-            else if (e.Key == Key.Up)
-            {
-                SlashPopup_ScrollByDelta(120); // 위로 1칸
+                return true;
+            case Key.Up:
+                SlashPopup_ScrollByDelta(120);
                 e.Handled = true;
-            }
-            else if (e.Key == Key.Down)
-            {
-                SlashPopup_ScrollByDelta(-120); // 아래로 1칸
+                return true;
+            case Key.Down:
+                SlashPopup_ScrollByDelta(-120);
                 e.Handled = true;
-            }
-            else if (e.Key == Key.PageUp)
-            {
+                return true;
+            case Key.PageUp:
                 SlashPopup_ScrollByDelta(600);
                 e.Handled = true;
-            }
-            else if (e.Key == Key.PageDown)
-            {
+                return true;
+            case Key.PageDown:
                 SlashPopup_ScrollByDelta(-600);
                 e.Handled = true;
-            }
-            else if (e.Key == Key.Home)
+                return true;
+            case Key.Home:
             {
                 var visible = GetVisibleSlashOrderedIndices();
                 _slashPalette.SelectedIndex = visible.Count > 0 ? visible[0] : GetFirstVisibleSlashIndex(_slashPalette.Matches);
                 UpdateSlashSelectionVisualState();
                 EnsureSlashSelectionVisible();
                 e.Handled = true;
+                return true;
             }
-            else if (e.Key == Key.End)
+            case Key.End:
             {
                 var visible = GetVisibleSlashOrderedIndices();
                 _slashPalette.SelectedIndex = visible.Count > 0 ? visible[^1] : GetFirstVisibleSlashIndex(_slashPalette.Matches);
                 UpdateSlashSelectionVisualState();
                 EnsureSlashSelectionVisible();
                 e.Handled = true;
+                return true;
             }
-            else if (e.Key == Key.Enter && _slashPalette.SelectedIndex >= 0)
-            {
-                e.Handled = true;
+            case Key.Tab when _slashPalette.SelectedIndex >= 0:
+            case Key.Enter when _slashPalette.SelectedIndex >= 0:
                 ExecuteSlashSelectedItem();
-            }
-        }
-
-        if (PermissionPopup.IsOpen && e.Key == Key.Escape)
-        {
-            PermissionPopup.IsOpen = false;
-            e.Handled = true;
+                e.Handled = true;
+                return true;
+            default:
+                return false;
         }
     }