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/Islands/DetailsIslandViewModel.cs

@@ -165,6 +165,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
     {
         OnPropertyChanged(nameof(HasChildOutcomes));
         OnPropertyChanged(nameof(ShowMergeSection));
+        NotifyAttention();
 
         // The Session tab is only visible when it has outcomes; if it just
         // emptied while selected, fall back to Output so the body isn't blank.
@@ -354,7 +355,11 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
 
     [ObservableProperty] private string? _worktreePath;
     [ObservableProperty] private string? _worktreeBaseCommit;
+    [ObservableProperty] private string? _worktreeHeadCommit;
     [ObservableProperty] private string? _worktreeStateLabel;
+    // Repo working dir of the selected task's list — used to diff a merged task's
+    // commit range after its worktree directory is gone.
+    private string? _listWorkingDir;
     [ObservableProperty] private string? _branchLine;
     [ObservableProperty] private int _turns;
     [ObservableProperty] private int _tokens;
@@ -388,6 +393,27 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
     public ObservableCollection<ChildOutcomeRowViewModel> ChildOutcomes { get; } = new();
     public bool HasChildOutcomes => ChildOutcomes.Count > 0;
 
+    // Children that need the user's attention before the parent can be approved:
+    // failed, cancelled, still awaiting their own review, or that reported roadblocks.
+    // The parent deliberately stays in WaitingForChildren until these are resolved;
+    // this surfaces a flag so the roadblock is visible on the parent.
+    public int ChildrenNeedingAttention => ChildOutcomes.Count(c =>
+        c.Status == ClaudeDo.Data.Models.TaskStatus.Failed
+        || c.Status == ClaudeDo.Data.Models.TaskStatus.Cancelled
+        || c.Status == ClaudeDo.Data.Models.TaskStatus.WaitingForReview
+        || c.RoadblockCount > 0);
+    public bool HasChildrenNeedingAttention => ChildrenNeedingAttention > 0;
+    public string ChildrenAttentionText => ChildrenNeedingAttention == 1
+        ? "1 child needs attention"
+        : $"{ChildrenNeedingAttention} children need attention";
+
+    private void NotifyAttention()
+    {
+        OnPropertyChanged(nameof(ChildrenNeedingAttention));
+        OnPropertyChanged(nameof(HasChildrenNeedingAttention));
+        OnPropertyChanged(nameof(ChildrenAttentionText));
+    }
+
     [ObservableProperty] private string _newSubtaskTitle = "";
 
     // Planning merge controls
@@ -840,6 +866,8 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             EditableDescription = "";
             Model = null;
             WorktreePath = null;
+            WorktreeHeadCommit = null;
+            _listWorkingDir = null;
             WorktreeStateLabel = null;
             BranchLine = null;
             DiffAdditions = 0;
@@ -876,6 +904,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             var entity = await ctx.Tasks
                 .AsNoTracking()
                 .Include(t => t.Worktree)
+                .Include(t => t.List)
                 .FirstOrDefaultAsync(t => t.Id == row.Id, ct);
             ct.ThrowIfCancellationRequested();
             if (entity == null) return;
@@ -885,8 +914,10 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             try { EditableDescription = entity.Description ?? ""; }
             finally { _suppressDescSave = false; }
             Model = entity.Model;
+            _listWorkingDir = entity.List?.WorkingDir;
             WorktreePath = entity.Worktree?.Path;
             WorktreeBaseCommit = entity.Worktree?.BaseCommit;
+            WorktreeHeadCommit = entity.Worktree?.HeadCommit;
             WorktreeStateLabel = entity.Worktree?.State.ToString();
             BranchLine = entity.Worktree is { } w ? $"{w.BranchName} \u2190 main" : null;
             var (add, del) = ParseDiffStat(entity.Worktree?.DiffStat);
@@ -914,13 +945,12 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
                 Subtasks.Add(new SubtaskRowViewModel { Id = s.Id, Title = s.Title, Done = s.Completed });
 
             if (entity.PlanningPhase != ClaudeDo.Data.Models.PlanningPhase.None)
-            {
                 await LoadPlanningChildrenAsync(row.Id, ct);
-            }
-            else
-            {
-                await LoadChildOutcomesAsync(row.Id, ct);
-            }
+            // Surface every parent's children — planning or improvement — in the
+            // Session tab with their live status + roadblock count. This is what
+            // makes the Session tab appear for planning parents and lets a child's
+            // roadblock register on the parent.
+            await LoadChildOutcomesAsync(row.Id, ct);
 
             if (entity.Worktree != null
                 && entity.PlanningPhase == ClaudeDo.Data.Models.PlanningPhase.None
@@ -1125,6 +1155,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             row.RoadblockCount = child.RoadblockCount;
             row.WorktreeState = child.Worktree?.State ?? ClaudeDo.Data.Models.WorktreeState.Active;
             ReviewCombinedDiffCommand.NotifyCanExecuteChanged();
+            NotifyAttention();
         }
         catch { /* best-effort */ }
     }
@@ -1148,11 +1179,14 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             var entity = await ctx.Tasks
                 .AsNoTracking()
                 .Include(t => t.Worktree)
+                .Include(t => t.List)
                 .FirstOrDefaultAsync(t => t.Id == taskId);
             if (entity == null || Task?.Id != taskId) return;
 
+            _listWorkingDir = entity.List?.WorkingDir;
             WorktreePath = entity.Worktree?.Path;
             WorktreeBaseCommit = entity.Worktree?.BaseCommit;
+            WorktreeHeadCommit = entity.Worktree?.HeadCommit;
             WorktreeStateLabel = entity.Worktree?.State.ToString();
             BranchLine = entity.Worktree is { } w ? $"{w.BranchName} ← main" : null;
             AgentState = StatusToStateKey(entity.Status);
@@ -1190,21 +1224,53 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
     [RelayCommand(CanExecute = nameof(CanOpenDiff))]
     private async System.Threading.Tasks.Task OpenDiffAsync()
     {
-        if (WorktreePath == null || ShowDiffModal == null) return;
-        var diffVm = new DiffModalViewModel(_services.GetRequiredService<ClaudeDo.Data.Git.GitService>())
+        if (ShowDiffModal == null) return;
+        var git = _services.GetRequiredService<ClaudeDo.Data.Git.GitService>();
+
+        // Active worktree on disk → diff the worktree live (and allow merging from it).
+        var hasLiveWorktree =
+            WorktreePath != null
+            && WorktreeStateLabel == "Active"
+            && System.IO.Directory.Exists(WorktreePath);
+
+        DiffModalViewModel diffVm;
+        if (hasLiveWorktree)
         {
-            WorktreePath = WorktreePath,
-            BaseRef = WorktreeBaseCommit,
-            TaskId = Task?.Id,
-            TaskTitle = Task?.Title ?? "",
-            ShowMergeModal = ShowMergeModal,
-            ResolveMergeVm = () => _services.GetRequiredService<MergeModalViewModel>(),
-        };
+            diffVm = new DiffModalViewModel(git)
+            {
+                WorktreePath = WorktreePath!,
+                BaseRef = WorktreeBaseCommit,
+                TaskId = Task?.Id,
+                TaskTitle = Task?.Title ?? "",
+                ShowMergeModal = ShowMergeModal,
+                ResolveMergeVm = () => _services.GetRequiredService<MergeModalViewModel>(),
+            };
+        }
+        else if (CanDiffMergedRange)
+        {
+            // Worktree is gone (merged/discarded) but the commits survive on the
+            // target branch — diff the captured base..head range in the repo. No
+            // merge action: the work is already integrated.
+            diffVm = new DiffModalViewModel(git)
+            {
+                WorktreePath = _listWorkingDir!,
+                BaseRef = WorktreeBaseCommit,
+                HeadCommit = WorktreeHeadCommit,
+                FromCommitRange = true,
+                TaskId = Task?.Id,
+                TaskTitle = Task?.Title ?? "",
+            };
+        }
+        else return;
+
         await diffVm.LoadAsync();
         await ShowDiffModal(diffVm);
     }
 
-    private bool CanOpenDiff() => WorktreePath != null;
+    private bool CanDiffMergedRange =>
+        WorktreeBaseCommit != null && WorktreeHeadCommit != null && _listWorkingDir != null;
+
+    private bool CanOpenDiff() => WorktreePath != null || CanDiffMergedRange;
 
     [RelayCommand(CanExecute = nameof(CanOpenWorktree))]
     private void OpenWorktree()
@@ -1235,6 +1301,9 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         NotifySessionSections();
     }
 
+    partial void OnWorktreeHeadCommitChanged(string? value) =>
+        OpenDiffCommand.NotifyCanExecuteChanged();
+
     partial void OnTaskChanged(TaskRowViewModel? value) => NotifySessionSections();
 
     [RelayCommand]
@@ -1473,7 +1542,13 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             }
             // hasChildren: conflicts arrive via PlanningMergeConflictEvent → conflict dialog
         }
-        catch { /* stale review action; broadcast reconciles */ }
+        catch (Exception ex)
+        {
+            // A real failure (e.g. a child still needs attention, so the unit can't
+            // be approved yet) must not vanish — tell the user why nothing happened.
+            if (ShowErrorAsync != null)
+                await ShowErrorAsync(ex.Message);
+        }
     }
 
     [RelayCommand]