test(worker): strengthen DiscardAsync test (cleanup + branch assertion)

tests/ClaudeDo.Worker.Tests/Runner/WorktreeManagerTests.cs

@@ -191,6 +191,7 @@ public class WorktreeManagerTests : IDisposable
         var (mgr, db) = await CreateManagerAsync(task, list);
 
         var ctx = await mgr.CreateAsync(task, list, CancellationToken.None);
+        _worktreeCleanups.Add((repo.RepoDir, ctx.WorktreePath));
         var worktreePath = ctx.WorktreePath;
 
         WorktreeEntity wt;
@@ -201,6 +202,10 @@ public class WorktreeManagerTests : IDisposable
 
         Assert.False(Directory.Exists(worktreePath), "worktree directory should be gone");
 
+        var branchList = GitRepoFixture.RunGit(repo.RepoDir, "branch", "--list", ctx.BranchName);
+        Assert.True(string.IsNullOrWhiteSpace(branchList),
+            $"branch {ctx.BranchName} should be deleted, got: {branchList}");
+
         using var readCtx2 = db.CreateContext();
         var row = await new WorktreeRepository(readCtx2).GetByTaskIdAsync(task.Id);
         Assert.NotNull(row);