refactor(diff): render planning mode per file and retire DiffLinesView

src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs

@@ -3,7 +3,7 @@ using CommunityToolkit.Mvvm.ComponentModel;
 
 namespace ClaudeDo.Ui.ViewModels.Modals;
 
-// Shared diff models used by UnifiedDiffParser, DiffLinesView and DiffViewerViewModel.
+// Shared diff models used by UnifiedDiffParser, DiffTextView and DiffViewerViewModel.
 
 public enum DiffLineKind { Add, Del, Ctx, File }
 

src/ClaudeDo.Ui/ViewModels/Modals/DiffViewerViewModel.cs

@@ -56,7 +56,8 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
 
     // ── Right pane ──────────────────────────────────────────────────────────
     [ObservableProperty] private DiffFileViewModel? _selectedFile;       // Files mode
-    public ObservableCollection<DiffLineViewModel> DiffLines { get; } = new(); // Planning mode
+    // Planning mode: one entry per file so each gets its own editor and grammar.
+    public ObservableCollection<DiffFileViewModel> PlanningFiles { get; } = new();
     [ObservableProperty] private string _displayedDiff = "";
     [ObservableProperty] private string? _statusMessage;
 
@@ -250,9 +251,9 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
 
     partial void OnDisplayedDiffChanged(string value)
     {
-        DiffLines.Clear();
-        foreach (var line in UnifiedDiffParser.Flatten(UnifiedDiffParser.Parse(value)))
-            DiffLines.Add(line);
+        PlanningFiles.Clear();
+        foreach (var file in UnifiedDiffParser.Parse(value))
+            PlanningFiles.Add(file);
     }
 
     // ── Merge (Files mode, branch source) ───────────────────────────────────

src/ClaudeDo.Ui/ViewModels/Modals/UnifiedDiffParser.cs

@@ -132,21 +132,6 @@ public static class UnifiedDiffParser
         return files;
     }
 
-    /// Flattens multiple parsed files into a single line stream, inserting a
-    /// file-header row before each file so boundaries are visible in a
-    /// single-pane (combined) view.
-    public static List<DiffLineViewModel> Flatten(IEnumerable<DiffFileViewModel> files)
-    {
-        var lines = new List<DiffLineViewModel>();
-        foreach (var file in files)
-        {
-            lines.Add(new DiffLineViewModel { Kind = DiffLineKind.File, Text = file.Path });
-            foreach (var line in file.Lines)
-                lines.Add(line);
-        }
-        return lines;
-    }
-
     private static void ParseHunkHeader(string header, out int oldStart, out int newStart)
     {
         oldStart = 1; newStart = 1;