feat(worker): use the list base branch as worktree base and default merge target

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

@@ -425,6 +425,30 @@ public class WorktreeManagerTests : IDisposable
         Assert.StartsWith("chore/77-test-task", ctx.BranchName);
     }
 
+    [Fact]
+    public async Task CreateAsync_BaseBranchSet_BasesOnItEvenWhenAnotherBranchIsCheckedOut()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var repo = CreateRepo();
+        GitRepoFixture.RunGit(repo.RepoDir, "checkout", "-b", "dev");
+        File.WriteAllText(Path.Combine(repo.RepoDir, "dev.txt"), "dev");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "dev work");
+        var devHead = GitRepoFixture.RunGit(repo.RepoDir, "rev-parse", "HEAD").Trim();
+        GitRepoFixture.RunGit(repo.RepoDir, "checkout", "-b", "elsewhere", repo.BaseCommit);
+
+        var (task, list) = MakeEntities(repo.RepoDir);
+        var (mgr, db) = await CreateManagerAsync(task, list);
+        using (var ctx0 = db.CreateContext())
+            await new ListRepository(ctx0).SetConfigAsync(new ListConfigEntity { ListId = list.Id, BaseBranch = "dev" });
+
+        var ctx = await mgr.CreateAsync(task, list, CancellationToken.None);
+        _worktreeCleanups.Add((repo.RepoDir, ctx.WorktreePath));
+
+        Assert.Equal(devHead, ctx.BaseCommit);
+    }
+
     private static (TaskEntity task, ListEntity list) MakeEntities(string workingDir)
     {
         var listId = Guid.NewGuid().ToString();

tests/ClaudeDo.Worker.Tests/Services/TaskMergeServiceTests.cs

@@ -1092,6 +1092,74 @@ public class TaskMergeServiceTests : IDisposable
         Assert.False(Directory.Exists(wtCtx.WorktreePath));
     }
 
+    [Fact]
+    public async Task GetTargetsAsync_prefers_list_base_branch()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        GitRepoFixture.RunGit(repo.RepoDir, "branch", "dev");
+        var db = NewDb();
+        var (list, task) = await SeedListAndTask(db, workingDir: repo.RepoDir, status: TaskStatus.Done);
+        using (var ctx = db.CreateContext())
+            await new ListRepository(ctx).SetConfigAsync(new ListConfigEntity { ListId = list.Id, BaseBranch = "dev" });
+
+        var (svc, _) = BuildService(db);
+        var targets = await svc.GetTargetsAsync(task.Id, CancellationToken.None);
+
+        Assert.NotEqual("dev", await new GitService().GetCurrentBranchAsync(repo.RepoDir));
+        Assert.Equal("dev", targets.DefaultBranch);
+    }
+
+    [Fact]
+    public async Task ApproveAndMergeAsync_EmptyTarget_MergesIntoListBaseBranch()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        GitRepoFixture.RunGit(repo.RepoDir, "branch", "dev");
+        var original = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+        var db = NewDb();
+        var (list, task) = await SeedListAndTask(db, repo.RepoDir, TaskStatus.WaitingForReview);
+        using (var ctx0 = db.CreateContext())
+            await new ListRepository(ctx0).SetConfigAsync(new ListConfigEntity { ListId = list.Id, BaseBranch = "dev" });
+
+        var wtMgr = BuildWorktreeManager(db);
+        var wtCtx = await wtMgr.CreateAsync(task, list, CancellationToken.None);
+        _wtCleanups.Add((repo.RepoDir, wtCtx.WorktreePath));
+        File.WriteAllText(Path.Combine(wtCtx.WorktreePath, "added.txt"), "new\n");
+        await wtMgr.CommitIfChangedAsync(wtCtx, task, list, CancellationToken.None);
+
+        var (svc, _) = BuildService(db);
+        var result = await svc.ApproveAndMergeAsync(task.Id, "", CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusMerged, result.Status);
+        Assert.Contains("added.txt", GitRepoFixture.RunGit(repo.RepoDir, "ls-tree", "--name-only", "dev"));
+        Assert.Equal(repo.BaseCommit, GitRepoFixture.RunGit(repo.RepoDir, "rev-parse", original).Trim());
+    }
+
+    [Fact]
+    public async Task MergeAsync_EmptyTarget_MergesIntoCheckedOutBranch()
+    {
+        // PlanningMergeOrchestrator.DrainAsync passes an empty target straight through — that used
+        // to end in `git checkout ""` -> Blocked.
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        var current = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+        var db = NewDb();
+        var (list, task) = await SeedListAndTask(db, repo.RepoDir, TaskStatus.WaitingForReview);
+
+        var wtMgr = BuildWorktreeManager(db);
+        var wtCtx = await wtMgr.CreateAsync(task, list, CancellationToken.None);
+        _wtCleanups.Add((repo.RepoDir, wtCtx.WorktreePath));
+        File.WriteAllText(Path.Combine(wtCtx.WorktreePath, "added.txt"), "new\n");
+        await wtMgr.CommitIfChangedAsync(wtCtx, task, list, CancellationToken.None);
+
+        var (svc, _) = BuildService(db);
+        var result = await svc.MergeAsync(task.Id, "", false, "msg", CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusMerged, result.Status);
+        Assert.Contains("added.txt", GitRepoFixture.RunGit(repo.RepoDir, "ls-tree", "--name-only", current));
+    }
+
     [Fact]
     public async Task ApproveAndMergeAsync_Conflict_LeavesTaskWaitingForReview()
     {