refactor(worker): make the list-handler launch spec single-list and single-repo

src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs

@@ -86,8 +86,8 @@ public interface IWorkerClient : INotifyPropertyChanged
     /// no task, no worktree.</summary>
     Task<LaunchSpec> GetAdHocLaunchSpecAsync(string directory, CancellationToken ct = default);
     /// <summary>Launch spec for an embedded ConPTY "merge helper" session that drives the given
-    /// tasks to a merged/Done state. listId scopes the session to that list; null = all lists.</summary>
-    Task<LaunchSpec> GetMergeHelperLaunchSpecAsync(IReadOnlyList<string> taskIds, string? listId, CancellationToken ct = default);
+    /// tasks to a merged/Done state. listId scopes the session (and cwd) to that list.</summary>
+    Task<LaunchSpec> GetMergeHelperLaunchSpecAsync(IReadOnlyList<string> taskIds, string listId, CancellationToken ct = default);
     /// <summary>Starts a planning session and returns the launch spec for an embedded ConPTY
     /// planning terminal (replaces StartPlanningSessionAsync's external wt window).</summary>
     Task<LaunchSpec> GetPlanningStartLaunchSpecAsync(string taskId, CancellationToken ct = default);

src/ClaudeDo.Ui/Services/WorkerClient.cs

@@ -522,7 +522,7 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public async Task<LaunchSpec> GetAdHocLaunchSpecAsync(string directory, CancellationToken ct = default)
         => await _hub.InvokeAsync<LaunchSpec>("GetAdHocLaunchSpec", directory, ct);
 
-    public async Task<LaunchSpec> GetMergeHelperLaunchSpecAsync(IReadOnlyList<string> taskIds, string? listId, CancellationToken ct = default)
+    public async Task<LaunchSpec> GetMergeHelperLaunchSpecAsync(IReadOnlyList<string> taskIds, string listId, CancellationToken ct = default)
         => await _hub.InvokeAsync<LaunchSpec>("GetMergeHelperLaunchSpec", taskIds, listId, ct);
 
     public async Task<LaunchSpec> GetPlanningStartLaunchSpecAsync(string taskId, CancellationToken ct = default)