feat(ui): richer diff viewer + surface child roadblocks on parents

- UnifiedDiffParser detects added/deleted/renamed/binary files; diff
  modal shows a file list, binary/empty placeholders, and can diff a
  merged task by commit range after its worktree is gone
- DetailsIslandViewModel flags children needing attention (failed,
  cancelled, awaiting review, or with roadblocks) on the parent
- GitService gains worktree head-commit/range support; planning chain,
  merge orchestration, and session manager tweaks with updated tests
- refresh app/installer/worker icons

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -8,6 +8,8 @@ namespace ClaudeDo.Ui.ViewModels.Modals;
 
 public enum DiffLineKind { Add, Del, Ctx, File }
 
+public enum DiffFileStatus { Modified, Added, Deleted, Renamed }
+
 public sealed class DiffLineViewModel
 {
     public required DiffLineKind Kind { get; init; }
@@ -32,10 +34,27 @@ public sealed class DiffLineViewModel
 
 public sealed class DiffFileViewModel
 {
-    public required string Path { get; init; }
+    public required string Path { get; set; }
+    public string? OldPath { get; set; }
+    public DiffFileStatus Status { get; set; } = DiffFileStatus.Modified;
+    public bool IsBinary { get; set; }
     public int Additions { get; set; }
     public int Deletions { get; set; }
     public ObservableCollection<DiffLineViewModel> Lines { get; } = new();
+
+    /// Single-letter badge for the file's change kind (A/M/D/R).
+    public string StatusCode => Status switch
+    {
+        DiffFileStatus.Added    => "A",
+        DiffFileStatus.Deleted  => "D",
+        DiffFileStatus.Renamed  => "R",
+        _                       => "M",
+    };
+
+    public bool HasLines => Lines.Count > 0;
+
+    /// A text file that produced no diff hunks (e.g. a newly added empty file).
+    public bool IsEmptyContent => !IsBinary && Lines.Count == 0;
 }
 
 public sealed partial class DiffModalViewModel : ViewModelBase
@@ -44,6 +63,11 @@ public sealed partial class DiffModalViewModel : ViewModelBase
 
     public required string WorktreePath { get; init; }
     public string? BaseRef { get; init; }
+    /// When set together with <see cref="FromCommitRange"/>, the diff is computed as
+    /// <c>BaseRef..HeadCommit</c> inside <see cref="WorktreePath"/> (used as the repo
+    /// dir) — lets a merged task's diff be viewed after its worktree is gone.
+    public string? HeadCommit { get; init; }
+    public bool FromCommitRange { get; init; }
     public string? TaskId { get; init; }
     public string TaskTitle { get; init; } = "";
     public Func<MergeModalViewModel, Task>? ShowMergeModal { get; set; }
@@ -77,6 +101,8 @@ public sealed partial class DiffModalViewModel : ViewModelBase
         var vm = ResolveMergeVm();
         await vm.InitializeAsync(TaskId, TaskTitle);
         await ShowMergeModal(vm);
+        // The diff is stale once the worktree has been merged away — close it too.
+        if (vm.Merged) CloseAction?.Invoke();
     }
 
     public async Task LoadAsync(CancellationToken ct = default)
@@ -87,9 +113,11 @@ public sealed partial class DiffModalViewModel : ViewModelBase
         string raw;
         try
         {
-            raw = BaseRef is not null
-                ? await _git.GetBranchDiffAsync(WorktreePath, BaseRef, ct)
-                : await _git.GetDiffAsync(WorktreePath, ct);
+            raw = FromCommitRange && BaseRef is not null && HeadCommit is not null
+                ? await _git.GetCommitRangeDiffAsync(WorktreePath, BaseRef, HeadCommit, ct)
+                : BaseRef is not null
+                    ? await _git.GetBranchDiffAsync(WorktreePath, BaseRef, ct)
+                    : await _git.GetDiffAsync(WorktreePath, ct);
         }
         catch (Exception ex)
         {

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

@@ -28,6 +28,10 @@ public sealed partial class MergeModalViewModel : ViewModelBase
 
     public Action? CloseAction { get; set; }
 
+    /// True once a merge has succeeded — lets the caller (e.g. the diff window)
+    /// close itself after this modal closes.
+    public bool Merged { get; private set; }
+
     public MergeModalViewModel(WorkerClient worker)
     {
         _worker = worker;
@@ -80,6 +84,7 @@ public sealed partial class MergeModalViewModel : ViewModelBase
             switch (result.Status)
             {
                 case "merged":
+                    Merged = true;
                     SuccessMessage = result.ErrorMessage is not null
                         ? $"Merged with warning: {result.ErrorMessage}"
                         : Loc.T("vm.merge.merged");

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

@@ -27,6 +27,36 @@ public static class UnifiedDiffParser
 
             if (current == null) continue;
 
+            // File-level metadata that carries the change kind.
+            if (line.StartsWith("new file", StringComparison.Ordinal))
+            {
+                current.Status = DiffFileStatus.Added;
+                continue;
+            }
+            if (line.StartsWith("deleted file", StringComparison.Ordinal))
+            {
+                current.Status = DiffFileStatus.Deleted;
+                continue;
+            }
+            if (line.StartsWith("rename from ", StringComparison.Ordinal))
+            {
+                current.Status = DiffFileStatus.Renamed;
+                current.OldPath = line["rename from ".Length..];
+                continue;
+            }
+            if (line.StartsWith("rename to ", StringComparison.Ordinal))
+            {
+                current.Status = DiffFileStatus.Renamed;
+                current.Path = line["rename to ".Length..];
+                continue;
+            }
+            if (line.StartsWith("Binary files", StringComparison.Ordinal) ||
+                line.StartsWith("GIT binary patch", StringComparison.Ordinal))
+            {
+                current.IsBinary = true;
+                continue;
+            }
+
             if (line.StartsWith("@@ ", StringComparison.Ordinal))
             {
                 // e.g. "@@ -10,7 +10,9 @@"
@@ -34,13 +64,15 @@ public static class UnifiedDiffParser
                 continue;
             }
 
-            // Skip diff metadata lines
+            // Skip remaining diff metadata lines
             if (line.StartsWith("--- ", StringComparison.Ordinal) ||
                 line.StartsWith("+++ ", StringComparison.Ordinal) ||
                 line.StartsWith("index ", StringComparison.Ordinal) ||
-                line.StartsWith("new file", StringComparison.Ordinal) ||
-                line.StartsWith("deleted file", StringComparison.Ordinal) ||
-                line.StartsWith("Binary ", StringComparison.Ordinal))
+                line.StartsWith("old mode", StringComparison.Ordinal) ||
+                line.StartsWith("new mode", StringComparison.Ordinal) ||
+                line.StartsWith("similarity index", StringComparison.Ordinal) ||
+                line.StartsWith("copy from", StringComparison.Ordinal) ||
+                line.StartsWith("copy to", StringComparison.Ordinal))
                 continue;
 
             if (line.StartsWith('+'))