refactor(merge): single IMergeCoordinator replaces the 5 conflict seams

The RequestConflictResolution Func was declared on 5 VMs and hand-threaded shell->details->merge-section->diff->merge-modal. Replaced with a DI-singleton IMergeCoordinator (MergeCoordinator holder; shell wires its Handler at composition, breaking the shell<->island cycle). Invokers (MergeModal, DetailsIsland, WorktreesOverview) depend on the interface; the two pass-through VMs (DiffModal, MergeSection) drop the seam entirely. No behavior change; conflict-seam + batch tests rewired to assert via the coordinator.

src/ClaudeDo.App/Program.cs

@@ -116,6 +116,10 @@ sealed class Program
             return new UpdateCheckService(releases, version);
         });
 
+        // Conflict-merge coordinator: single seam the shell wires to its resolver entry.
+        sc.AddSingleton<MergeCoordinator>();
+        sc.AddSingleton<IMergeCoordinator>(sp => sp.GetRequiredService<MergeCoordinator>());
+
         // ViewModels
         sc.AddTransient<WorktreeModalViewModel>();
         sc.AddTransient<Func<WorktreeModalViewModel>>(sp => () => sp.GetRequiredService<WorktreeModalViewModel>());
@@ -152,12 +156,14 @@ sealed class Program
                 sp.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>(),
                 sp.GetRequiredService<IWorkerClient>(),
                 sp,
-                sp.GetRequiredService<INotesApi>()));
+                sp.GetRequiredService<INotesApi>(),
+                sp.GetRequiredService<IMergeCoordinator>()));
         sc.AddSingleton<IslandsShellViewModel>(sp =>
         {
             var shell = ActivatorUtilities.CreateInstance<IslandsShellViewModel>(sp);
             shell.ConflictResolverFactory =
                 sp.GetRequiredService<Func<string, ClaudeDo.Ui.ViewModels.Conflicts.ConflictResolverViewModel>>();
+            sp.GetRequiredService<MergeCoordinator>().Handler = shell.RequestConflictResolutionAsync;
             return shell;
         });
 

src/ClaudeDo.Ui/Services/IMergeCoordinator.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Threading.Tasks;
+
+namespace ClaudeDo.Ui.Services;
+
+/// <summary>
+/// Single entry point for handing a conflicting merge to the in-app 3-pane resolver.
+/// Replaces the per-VM <c>RequestConflictResolution</c> Func seams that used to be
+/// hand-threaded shell → details → merge-section → diff → merge-modal. The shell wires
+/// <see cref="MergeCoordinator.Handler"/> once at composition; invokers depend only on
+/// this interface (injected via DI).
+/// </summary>
+public interface IMergeCoordinator
+{
+    Task ResolveConflictAsync(string taskId, string targetBranch);
+}
+
+/// <summary>
+/// DI singleton holding the resolver entry. The holder breaks the shell↔island construction
+/// cycle: islands depend on the interface, the shell sets <see cref="Handler"/> after it is built.
+/// </summary>
+public sealed class MergeCoordinator : IMergeCoordinator
+{
+    /// Set once at composition to the shell's resolver entry. Null (headless/tests) ⇒ no-op.
+    public Func<string, string, Task>? Handler { get; set; }
+
+    public Task ResolveConflictAsync(string taskId, string targetBranch) =>
+        Handler?.Invoke(taskId, targetBranch) ?? Task.CompletedTask;
+}

src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs

@@ -52,6 +52,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
     private readonly IWorkerClient _worker;
     private readonly IServiceProvider _services;
     private readonly INotesApi _notesApi;
+    private readonly IMergeCoordinator _merge;
 
     // ── Section view models ───────────────────────────────────────────────────
     public AgentSettingsSectionViewModel AgentSettings { get; }
@@ -343,13 +344,6 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
 
     public bool HasReviewFeedback => !string.IsNullOrWhiteSpace(ReviewFeedback);
 
-    // Kept for backwards-compat surface — delegates to Merge.RequestConflictResolution
-    public Func<string, string, System.Threading.Tasks.Task>? RequestConflictResolution
-    {
-        get => Merge.RequestConflictResolution;
-        set => Merge.RequestConflictResolution = value;
-    }
-
     private static string StatusToStateKey(ClaudeDo.Data.Models.TaskStatus status) => status switch
     {
         ClaudeDo.Data.Models.TaskStatus.Queued           => "queued",
@@ -404,12 +398,14 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         IDbContextFactory<ClaudeDoDbContext> dbFactory,
         IWorkerClient worker,
         IServiceProvider services,
-        INotesApi notesApi)
+        INotesApi notesApi,
+        IMergeCoordinator merge)
     {
         _dbFactory = dbFactory;
         _worker = worker;
         _services = services;
         _notesApi = notesApi;
+        _merge = merge;
 
         AgentSettings = new AgentSettingsSectionViewModel(worker);
         Merge = new MergeSectionViewModel(worker, services);
@@ -1151,20 +1147,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             var hasChildren = Subtasks.Count > 0 || ChildOutcomes.Count > 0;
             var result = await _worker.ApproveReviewAsync(Task.Id, Merge.SelectedMergeTarget ?? "");
             if (!hasChildren && result?.Status == "conflict")
-            {
+                await _merge.ResolveConflictAsync(Task.Id, Merge.SelectedMergeTarget ?? "");
-                if (Merge.RequestConflictResolution is not null)
-                {
-                    await Merge.RequestConflictResolution(Task.Id, Merge.SelectedMergeTarget ?? "");
-                }
-                else
-                {
-                    var (text, _, _) = MergePreviewPresenter.Describe(
-                        new MergePreviewDto("conflict", result.ConflictFiles, 0));
-                    Merge.MergePreviewText = text;
-                    Merge.MergeIsClean = false;
-                    Merge.MergeIsConflict = true;
-                }
-            }
         }
         catch (Exception ex)
         {

src/ClaudeDo.Ui/ViewModels/Islands/MergeSectionViewModel.cs

@@ -48,7 +48,6 @@ public sealed partial class MergeSectionViewModel : ViewModelBase
     public Func<DiffModalViewModel, System.Threading.Tasks.Task>? ShowDiffModal { get; set; }
     public Func<MergeModalViewModel, System.Threading.Tasks.Task>? ShowMergeModal { get; set; }
     public Func<ViewModels.Planning.PlanningDiffViewModel, System.Threading.Tasks.Task>? ShowPlanningDiffModal { get; set; }
-    public Func<string, string, System.Threading.Tasks.Task>? RequestConflictResolution { get; set; }
 
     public MergeSectionViewModel(IWorkerClient worker, IServiceProvider services)
     {
@@ -156,7 +155,6 @@ public sealed partial class MergeSectionViewModel : ViewModelBase
                 TaskTitle = TaskTitle ?? "",
                 ShowMergeModal = ShowMergeModal,
                 ResolveMergeVm = () => _services.GetRequiredService<MergeModalViewModel>(),
-                RequestConflictResolution = RequestConflictResolution,
             };
         }
         else if (CanDiffMergedRange)

src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs

@@ -194,7 +194,6 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
             _ = Lists.RefreshCountsAsync();
             return System.Threading.Tasks.Task.CompletedTask;
         };
-        Details.RequestConflictResolution = RequestConflictResolutionAsync;
         Worker.PropertyChanged += (_, e) =>
         {
             if (e.PropertyName is nameof(IWorkerClient.IsConnected) or nameof(IWorkerClient.IsReconnecting))

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

@@ -72,7 +72,6 @@ public sealed partial class DiffModalViewModel : ViewModelBase
     public string TaskTitle { get; init; } = "";
     public Func<MergeModalViewModel, Task>? ShowMergeModal { get; set; }
     public Func<MergeModalViewModel>? ResolveMergeVm { get; set; }
-    public Func<string, string, Task>? RequestConflictResolution { get; set; }
 
     public ObservableCollection<DiffFileViewModel> Files { get; } = new();
 
@@ -100,7 +99,6 @@ public sealed partial class DiffModalViewModel : ViewModelBase
     {
         if (TaskId is null || ShowMergeModal is null || ResolveMergeVm is null) return;
         var vm = ResolveMergeVm();
-        vm.RequestConflictResolution = RequestConflictResolution;
         await vm.InitializeAsync(TaskId, TaskTitle);
         await ShowMergeModal(vm);
         // The diff is stale once the worktree merged away or a conflict opened the editor.

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

@@ -9,6 +9,7 @@ namespace ClaudeDo.Ui.ViewModels.Modals;
 public sealed partial class MergeModalViewModel : ViewModelBase
 {
     private readonly IWorkerClient _worker;
+    private readonly IMergeCoordinator _merge;
 
     public string TaskId { get; set; } = "";
     public string TaskTitle { get; set; } = "";
@@ -28,10 +29,6 @@ public sealed partial class MergeModalViewModel : ViewModelBase
 
     public Action? CloseAction { get; set; }
 
-    /// Set by the caller to hand a conflicting merge off to the in-app 3-pane editor
-    /// instead of dead-ending on the conflict message.
-    public Func<string, string, Task>? RequestConflictResolution { 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; }
@@ -39,9 +36,10 @@ public sealed partial class MergeModalViewModel : ViewModelBase
     /// True once a conflict has been handed off to the resolver — also a cue to close the diff window.
     public bool RoutedToResolver { get; private set; }
 
-    public MergeModalViewModel(IWorkerClient worker)
+    public MergeModalViewModel(IWorkerClient worker, IMergeCoordinator merge)
     {
         _worker = worker;
+        _merge = merge;
     }
 
     public async Task InitializeAsync(string taskId, string taskTitle)
@@ -103,21 +101,11 @@ public sealed partial class MergeModalViewModel : ViewModelBase
                     });
                     break;
                 case "conflict":
-                    // Hand off to the in-app 3-pane merge editor when wired (MergeTask aborted
+                    // MergeTask aborted cleanly; hand the conflict to the in-app 3-pane editor,
-                    // cleanly, so the resolver re-starts the merge leaving conflicts in the tree).
+                    // which re-starts the merge leaving conflicts in the tree.
-                    if (RequestConflictResolution is not null)
-                    {
-                        var branch = SelectedBranch!;
                     RoutedToResolver = true;
                     CloseAction?.Invoke();
-                        await RequestConflictResolution(TaskId, branch);
+                    await _merge.ResolveConflictAsync(TaskId, SelectedBranch!);
-                    }
-                    else
-                    {
-                        HasConflict = true;
-                        ConflictFiles = result.ConflictFiles;
-                        ErrorMessage = Loc.T("vm.merge.conflict");
-                    }
                     break;
                 case "blocked":
                     ErrorMessage = Loc.T("vm.merge.blocked", result.ErrorMessage ?? "");

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

@@ -62,6 +62,7 @@ public sealed partial class WorktreesOverviewModalViewModel : ViewModelBase
 {
     private readonly IWorkerClient _worker;
     private readonly Func<WorktreeModalViewModel> _diffVmFactory;
+    private readonly IMergeCoordinator _merge;
 
     [ObservableProperty] private string? _listIdFilter;
     [ObservableProperty] private string _title = "Worktrees";
@@ -79,9 +80,6 @@ public sealed partial class WorktreesOverviewModalViewModel : ViewModelBase
     public ObservableCollection<string> MergeTargets { get; } = new();
     public ObservableCollection<WorktreeOverviewRowViewModel> ConflictRows { get; } = new();
 
-    /// Inert seam wired by the integrator to Layer C's resolver at merge time. (taskId, targetBranch)
-    public Func<string, string, Task>? RequestConflictResolution { get; set; }
-
     public Action? CloseAction { get; set; }
     public Action<WorktreeModalViewModel>? ShowDiffAction { get; set; }
     public Action<string, string>? JumpToTaskAction { get; set; }
@@ -89,10 +87,11 @@ public sealed partial class WorktreesOverviewModalViewModel : ViewModelBase
     public Func<MergeModalViewModel>? ResolveMergeVm { get; set; }
     public Func<MergeModalViewModel, Task>? ShowMergeAction { get; set; }
 
-    public WorktreesOverviewModalViewModel(IWorkerClient worker, Func<WorktreeModalViewModel> diffVmFactory)
+    public WorktreesOverviewModalViewModel(IWorkerClient worker, Func<WorktreeModalViewModel> diffVmFactory, IMergeCoordinator merge)
     {
         _worker = worker;
         _diffVmFactory = diffVmFactory;
+        _merge = merge;
     }
 
     public void SelectRow(WorktreeOverviewRowViewModel row)
@@ -328,7 +327,7 @@ public sealed partial class WorktreesOverviewModalViewModel : ViewModelBase
     private void ResolveConflict(WorktreeOverviewRowViewModel? row)
     {
         if (row is null) return;
-        RequestConflictResolution?.Invoke(row.TaskId, SelectedTarget ?? "");
+        _ = _merge.ResolveConflictAsync(row.TaskId, SelectedTarget ?? "");
     }
 
     [RelayCommand]

src/ClaudeDo.Ui/Views/WindowDialogService.cs

@@ -87,8 +87,6 @@ public sealed class WindowDialogService : IDialogService
                 var mergeDlg = new MergeModalView { DataContext = mergeVm };
                 await mergeDlg.ShowDialog(_owner);
             };
-            vm.RequestConflictResolution = (taskId, target) =>
-                shell.RequestConflictResolutionAsync(taskId, target);
         }
         await dlg.ShowDialog(_owner);
     }

tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandConflictSeamTests.cs

@@ -64,10 +64,10 @@ public class DetailsIslandConflictSeamTests : IDisposable
             Task.FromResult<MergeResultDto?>(new MergeResultDto("conflict", new[] { "a.cs" }, null));
     }
 
-    private DetailsIslandViewModel BuildVm(StubWorkerClient worker)
+    private DetailsIslandViewModel BuildVm(StubWorkerClient worker, IMergeCoordinator merge)
     {
         var factory = new TestDbFactory(NewContext);
-        return new DetailsIslandViewModel(factory, worker, new NullServiceProvider(), new StubNotesApi());
+        return new DetailsIslandViewModel(factory, worker, new NullServiceProvider(), new StubNotesApi(), merge);
     }
 
     [Fact]
@@ -75,19 +75,22 @@ public class DetailsIslandConflictSeamTests : IDisposable
     {
         const string taskId = "task-conflict-1";
 
-        var vm = BuildVm(new ConflictApproveWorkerClient());
-        vm.Bind(new TaskRowViewModel { Id = taskId, Status = TaskStatus.WaitingForReview });
-        vm.Merge.SelectedMergeTarget = "main";
-
         string? capturedTaskId = null;
         string? capturedTarget = null;
-        vm.Merge.RequestConflictResolution = (tid, target) =>
+        var coordinator = new MergeCoordinator
+        {
+            Handler = (tid, target) =>
             {
                 capturedTaskId = tid;
                 capturedTarget = target;
                 return Task.CompletedTask;
+            },
         };
 
+        var vm = BuildVm(new ConflictApproveWorkerClient(), coordinator);
+        vm.Bind(new TaskRowViewModel { Id = taskId, Status = TaskStatus.WaitingForReview });
+        vm.Merge.SelectedMergeTarget = "main";
+
         await vm.ApproveReviewCommand.ExecuteAsync(null);
 
         Assert.Equal(taskId, capturedTaskId);

tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandPlanningTests.cs

@@ -66,7 +66,7 @@ public class DetailsIslandPlanningTests : IDisposable
     private DetailsIslandViewModel BuildVm(StubWorkerClient worker)
     {
         var factory = new TestDbFactory(NewContext);
-        return new DetailsIslandViewModel(factory, worker, new NullServiceProvider(), new StubNotesApi());
+        return new DetailsIslandViewModel(factory, worker, new NullServiceProvider(), new StubNotesApi(), new ClaudeDo.Ui.Services.MergeCoordinator());
     }
 
     // Connected worker whose review calls fail the way the hub does when the task

tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandPrepModeTests.cs

@@ -51,7 +51,7 @@ public class DetailsIslandPrepModeTests : IDisposable
     private DetailsIslandViewModel NewDetailsVm(StubWorkerClient stub)
     {
         var factory = new TestDbFactory(NewContext);
-        return new DetailsIslandViewModel(factory, stub, new NullServiceProvider(), new StubNotesApi());
+        return new DetailsIslandViewModel(factory, stub, new NullServiceProvider(), new StubNotesApi(), new ClaudeDo.Ui.Services.MergeCoordinator());
     }
 
     private sealed class NullServiceProvider : IServiceProvider

tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandReviewActionsTests.cs

@@ -69,7 +69,7 @@ public class DetailsIslandReviewActionsTests : IDisposable
     private DetailsIslandViewModel BuildVm(StubWorkerClient worker)
     {
         var factory = new TestDbFactory(NewContext);
-        return new DetailsIslandViewModel(factory, worker, new NullServiceProvider(), new StubNotesApi());
+        return new DetailsIslandViewModel(factory, worker, new NullServiceProvider(), new StubNotesApi(), new ClaudeDo.Ui.Services.MergeCoordinator());
     }
 
     [Fact]

tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandTabsTests.cs

@@ -57,7 +57,7 @@ public class DetailsIslandTabsTests : IDisposable
     private DetailsIslandViewModel NewVm()
     {
         var factory = new TestDbFactory(NewContext);
-        return new DetailsIslandViewModel(factory, new DefaultStub(), new NullServiceProvider(), new StubNotesApi());
+        return new DetailsIslandViewModel(factory, new DefaultStub(), new NullServiceProvider(), new StubNotesApi(), new ClaudeDo.Ui.Services.MergeCoordinator());
     }
 
     [Fact]

tests/ClaudeDo.Ui.Tests/ViewModels/WorktreesOverviewBatchMergeTests.cs

@@ -30,8 +30,9 @@ public class WorktreesOverviewBatchMergeTests
         Assert.False(row.IsConflict);
     }
 
-    private static WorktreesOverviewModalViewModel NewVm() =>
+    private static WorktreesOverviewModalViewModel NewVm(IMergeCoordinator? merge = null) =>
-        new(new ClaudeDo.Ui.Services.WorkerClient("http://127.0.0.1:1/hub"), () => null!);
+        new(new ClaudeDo.Ui.Services.WorkerClient("http://127.0.0.1:1/hub"), () => null!,
+            merge ?? new ClaudeDo.Ui.Services.MergeCoordinator());
 
     private static MergeResultDto Merged() => new("merged", System.Array.Empty<string>(), null);
     private static MergeResultDto Conflict() => new("conflict", new[] { "f.cs" }, null);
@@ -137,13 +138,15 @@ public class WorktreesOverviewBatchMergeTests
     [Fact]
     public void ResolveConflict_invokes_seam_with_task_and_target()
     {
-        var vm = NewVm();
+        (string Task, string Target)? captured = null;
+        var coordinator = new ClaudeDo.Ui.Services.MergeCoordinator
+        {
+            Handler = (taskId, target) => { captured = (taskId, target); return System.Threading.Tasks.Task.CompletedTask; },
+        };
+        var vm = NewVm(coordinator);
         vm.SelectedTarget = "release";
         var row = ActiveRow("x"); row.MergeOutcome = BatchMergeOutcome.Conflict;
 
-        (string Task, string Target)? captured = null;
-        vm.RequestConflictResolution = (taskId, target) => { captured = (taskId, target); return System.Threading.Tasks.Task.CompletedTask; };
-
         vm.ResolveConflictCommand.Execute(row);
 
         Assert.Equal(("x", "release"), captured);