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

src/ClaudeDo.Worker/Runner/Interfaces/IInteractiveLaunchSpecService.cs

@@ -30,8 +30,8 @@ public interface IInteractiveLaunchSpecService
     /// <summary>Builds a LaunchSpec for an embedded ConPTY "merge helper" session that drives the
     /// given tasks to a merged/Done state via the mcp__claudedo__* tools. Writes a per-session
     /// system prompt + task brief under ~/.todo-app/merge-helper-sessions/&lt;guid&gt; and exposes
-    /// that dir plus every distinct existing repo dir via --add-dir. listId scopes the brief label
-    /// and the cwd to that list; null means all lists (cwd = first existing repo dir). Throws
-    /// InvalidOperationException if taskIds is empty or no task has an existing working directory.</summary>
-    Task<LaunchSpec> BuildForMergeHelperAsync(IReadOnlyList<string> taskIds, string? listId, CancellationToken ct);
+    /// that dir plus the list's repo dir via --add-dir. cwd is the list's working directory.
+    /// Throws KeyNotFoundException if the list doesn't exist; InvalidOperationException if
+    /// taskIds is empty or the list has no existing working directory.</summary>
+    Task<LaunchSpec> BuildForMergeHelperAsync(IReadOnlyList<string> taskIds, string listId, CancellationToken ct);
 }