Preview: divider reaches both frame edges; Original / Split / Processed modes

CLAUDE.md

@@ -1299,6 +1299,13 @@ asserted in `shutdown_when_done_test.dart`:
   exact vertically (stretched horizontally by SAR). The shortcuts reach the
   widget's zoom through `MainViewModel.previewZoom`
   (`ComparisonZoomController`); `before_after_comparison_test.dart` covers it.
+- **Preview view mode (Original / Split / Processed)** is
+  `MainViewModel.previewViewMode` (shortcuts B / S / P), passed into the
+  controlled `BeforeAfterComparisonWidget`, so it survives scrubber moves and
+  new previews. The divider spans the full 0–1 of the panel (it was 5–95%,
+  which hid a typical left crop); line and handle are drawn inset at the
+  edges. Each mode draws only its side at its own aspect, and 1:1 measures the
+  frame on screen (Original: the source; otherwise the processed frame).
 - **Themes** are `AppTheme` in `theme_service.dart`, persisted as `appTheme`
   and provided above the MaterialApp. Theme-specific decoration beyond
   `ColorScheme` (Pride's stripe) goes through the `AppDecorations` theme

README.md

@@ -164,6 +164,7 @@ Every filter explains in place what it does and when to use it. Where two filter
 <summary><b>Preview, timeline and trimming</b></summary>
 
 - **Click** a thumbnail to jump there, or **drag** to scrub. The transport buttons step a frame at a time or jump to either end.
+- **Original / Split / Processed** (B / S / P) above the preview show either frame whole or both side by side; in Split, drag the divider all the way to either edge.
 - Zoom the preview with the **mouse wheel** or **pinch**; **double-click** resets it. **1:1** shows actual pixels, the way to judge fine detail, and **Fit** shows the whole frame.
 - The **mouse wheel** or **pinch** also zooms the timeline around the cursor, and **Shift+wheel** or a **two-finger swipe** pans it.
 - **Set In** / **Set Out** process only part of the source, handy for trying settings on a short section.
@@ -185,6 +186,7 @@ Every button with a shortcut shows it in its tooltip, and **?** lists them all.
 | Go to in / out point | ⇧I / ⇧O | Shift+I / Shift+O |
 | Clear in and out points | ⌥X | Alt+X |
 | Preview at actual pixels (1:1) / fit | ⌘1 / ⌘0 | Ctrl+1 / Ctrl+0 |
+| Show original / split / processed | B / S / P | B / S / P |
 | Zoom timeline in / out / to fit | = / - / \ | = / - / \ |
 | Add videos | ⌘O | Ctrl+O |
 | Start processing | ⌘↩ | Ctrl+Enter |

app/lib/models/app_shortcut.dart

@@ -89,6 +89,21 @@ enum AppShortcut {
     alternates: [LogicalKeyboardKey.numpad0],
     primary: true,
   ),
+  previewOriginal(
+    'Show original (before)',
+    AppShortcutGroup.preview,
+    LogicalKeyboardKey.keyB,
+  ),
+  previewSplit(
+    'Split original / processed',
+    AppShortcutGroup.preview,
+    LogicalKeyboardKey.keyS,
+  ),
+  previewProcessed(
+    'Show processed',
+    AppShortcutGroup.preview,
+    LogicalKeyboardKey.keyP,
+  ),
   zoomIn(
     'Zoom in',
     AppShortcutGroup.zoom,

app/lib/viewmodels/main_viewmodel.dart

@@ -34,6 +34,7 @@ import '../services/failure_log_writer.dart';
 import '../services/job_runner.dart';
 import '../services/system_shutdown.dart';
 import '../services/worker_manager.dart';
+import '../widgets/comparison_view_mode.dart';
 import '../widgets/comparison_zoom_controller.dart';
 
 /// The display aspect a processed preview is drawn at: its stored size with
@@ -151,6 +152,18 @@ class MainViewModel extends ChangeNotifier {
   /// view state held by the comparison; this lets the shortcuts reach it.
   final ComparisonZoomController previewZoom = ComparisonZoomController();
 
+  /// Original / Split / Processed on the before/after preview. Held here, not
+  /// in the comparison or on a queue item, so it survives scrubber moves, new
+  /// previews and switching videos.
+  ComparisonViewMode _previewViewMode = ComparisonViewMode.split;
+  ComparisonViewMode get previewViewMode => _previewViewMode;
+
+  void setPreviewViewMode(ComparisonViewMode mode) {
+    if (mode == _previewViewMode) return;
+    _previewViewMode = mode;
+    notifyListeners();
+  }
+
   // Shut down when the queue finishes (issue #123). Armed for one run only:
   // _stopProcessing disarms it, so a run the user cancelled can't leave it
   // armed, invisibly, for the next one.

app/lib/views/main_window.dart

@@ -16,6 +16,7 @@ import '../services/theme_service.dart';
 import '../models/app_shortcut.dart';
 import '../widgets/app_shortcut_scope.dart';
 import '../widgets/dynamic_range_badge.dart';
+import '../widgets/comparison_view_mode.dart';
 import 'keyboard_shortcuts_dialog.dart';
 import 'video_file_picker.dart';
 import '../viewmodels/main_viewmodel.dart';
@@ -112,6 +113,9 @@ class MainWindow extends StatelessWidget {
       AppShortcut.previewActualSize:
           whenPreviewing(viewModel.previewZoom.showActualSize),
       AppShortcut.previewFit: whenPreviewing(viewModel.previewZoom.fit),
+      for (final mode in ComparisonViewMode.values)
+        mode.shortcut:
+            whenPreviewing(() => viewModel.setPreviewViewMode(mode)),
       AppShortcut.zoomIn: whenPreviewing(viewModel.zoomIn),
       AppShortcut.zoomOut: whenPreviewing(viewModel.zoomOut),
       AppShortcut.zoomToFit: whenPreviewing(viewModel.resetTimelineZoom),

app/lib/views/preview_panel.dart

@@ -66,6 +66,8 @@ class _PreviewPanelState extends State<PreviewPanel> {
               beforeAspectRatio: viewModel.sourceDisplayAspect,
               afterAspectRatio: viewModel.comparisonAfterAspect,
               zoomController: viewModel.previewZoom,
+              viewMode: viewModel.previewViewMode,
+              onViewModeChanged: viewModel.setPreviewViewMode,
             ),
           ),