src/ClaudeDo.Data/Repositories/TaskRepository.cs

@@ -217,6 +217,56 @@ public sealed class TaskRepository
             .ToListAsync(ct);
     }
 
+    public async Task<TaskEntity> CreateChildAsync(
+        string parentId,
+        string title,
+        string? description,
+        IReadOnlyList<string>? tagNames,
+        string? commitType,
+        CancellationToken ct = default)
+    {
+        var parent = await _context.Tasks.FirstOrDefaultAsync(t => t.Id == parentId, ct);
+        if (parent is null)
+            throw new InvalidOperationException($"Parent task {parentId} not found.");
+
+        var maxSort = await _context.Tasks
+            .Where(t => t.ListId == parent.ListId)
+            .Select(t => (int?)t.SortOrder)
+            .MaxAsync(ct);
+
+        var child = new TaskEntity
+        {
+            Id = Guid.NewGuid().ToString(),
+            ListId = parent.ListId,
+            Title = title,
+            Description = description,
+            Status = TaskStatus.Draft,
+            CreatedAt = DateTime.UtcNow,
+            CommitType = string.IsNullOrEmpty(commitType) ? parent.CommitType : commitType,
+            ParentTaskId = parentId,
+            SortOrder = (maxSort ?? -1) + 1,
+        };
+        _context.Tasks.Add(child);
+
+        if (tagNames is not null && tagNames.Count > 0)
+        {
+            foreach (var tagName in tagNames.Distinct(StringComparer.OrdinalIgnoreCase))
+            {
+                var tag = await _context.Tags.FirstOrDefaultAsync(t => t.Name == tagName, ct);
+                if (tag is null)
+                {
+                    tag = new TagEntity { Name = tagName };
+                    _context.Tags.Add(tag);
+                    await _context.SaveChangesAsync(ct);
+                }
+                child.Tags.Add(tag);
+            }
+        }
+
+        await _context.SaveChangesAsync(ct);
+        return child;
+    }
+
     #endregion
 
     #region Queue selection

tests/ClaudeDo.Worker.Tests/Repositories/TaskRepositoryPlanningTests.cs

@@ -80,4 +80,43 @@ public sealed class TaskRepositoryPlanningTests : IDisposable
         Assert.Equal("b", children[0].Title);
         Assert.Equal("a", children[1].Title);
     }
+
+    [Fact]
+    public async Task CreateChildAsync_CreatesDraftUnderParent()
+    {
+        var listId = await CreateListAsync();
+        var parent = MakeTask(listId, TaskStatus.Planning);
+        await _tasks.AddAsync(parent);
+
+        var child = await _tasks.CreateChildAsync(
+            parent.Id,
+            title: "child title",
+            description: "child desc",
+            tagNames: new[] { "agent" },
+            commitType: "feat");
+
+        Assert.Equal(TaskStatus.Draft, child.Status);
+        Assert.Equal(parent.Id, child.ParentTaskId);
+        Assert.Equal(listId, child.ListId);
+        Assert.Equal("child title", child.Title);
+        Assert.Equal("child desc", child.Description);
+        Assert.Equal("feat", child.CommitType);
+
+        var loaded = await _tasks.GetByIdAsync(child.Id);
+        Assert.NotNull(loaded);
+        Assert.Equal(TaskStatus.Draft, loaded!.Status);
+
+        var tags = await _tasks.GetTagsAsync(child.Id);
+        Assert.Contains(tags, t => t.Name == "agent");
+    }
+
+    [Fact]
+    public async Task CreateChildAsync_ThrowsIfParentNotFound()
+    {
+        var listId = await CreateListAsync();
+        _ = listId; // just to create the DB
+
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            _tasks.CreateChildAsync("nonexistent-parent-id", "t", null, null, null));
+    }
 }