feat(data): add subtasks table, repository and prompt integration

Per-task checklist backend: subtasks table with CASCADE delete,
SubtaskEntity + SubtaskRepository (connection-per-op, async), DI
registration in App and Worker, TaskRunner composes a '## Sub-Tasks'
markdown block into the Claude prompt when subtasks exist.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.App/Program.cs

@@ -49,6 +49,7 @@ sealed class Program
         // Repositories
         sc.AddSingleton<ListRepository>();
         sc.AddSingleton<TaskRepository>();
+        sc.AddSingleton<SubtaskRepository>();
         sc.AddSingleton<TagRepository>();
         sc.AddSingleton<WorktreeRepository>();
 
@@ -66,7 +67,8 @@ sealed class Program
             sp.GetRequiredService<ListRepository>(),
             sp.GetRequiredService<GitService>(),
             sp.GetRequiredService<WorkerClient>(),
-            sp.GetRequiredService<TagRepository>()));
+            sp.GetRequiredService<TagRepository>(),
+            sp.GetRequiredService<SubtaskRepository>()));
         sc.AddSingleton<TaskListViewModel>(sp =>
         {
             var taskRepo = sp.GetRequiredService<TaskRepository>();

src/ClaudeDo.Data/Models/SubtaskEntity.cs

@@ -0,0 +1,11 @@
+namespace ClaudeDo.Data.Models;
+
+public sealed class SubtaskEntity
+{
+    public required string Id { get; init; }
+    public required string TaskId { get; init; }
+    public required string Title { get; set; }
+    public bool Completed { get; set; }
+    public int OrderNum { get; set; }
+    public required DateTime CreatedAt { get; init; }
+}

src/ClaudeDo.Data/Repositories/SubtaskRepository.cs

@@ -0,0 +1,81 @@
+using ClaudeDo.Data.Models;
+using Microsoft.Data.Sqlite;
+
+namespace ClaudeDo.Data.Repositories;
+
+public sealed class SubtaskRepository
+{
+    private readonly SqliteConnectionFactory _factory;
+
+    public SubtaskRepository(SqliteConnectionFactory factory) => _factory = factory;
+
+    public async Task<List<SubtaskEntity>> GetByTaskIdAsync(string taskId, CancellationToken ct = default)
+    {
+        await using var conn = _factory.Open();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = "SELECT id, task_id, title, completed, order_num, created_at FROM subtasks WHERE task_id = @task_id ORDER BY order_num";
+        cmd.Parameters.AddWithValue("@task_id", taskId);
+
+        await using var reader = await cmd.ExecuteReaderAsync(ct);
+        var result = new List<SubtaskEntity>();
+        while (await reader.ReadAsync(ct))
+            result.Add(ReadSubtask(reader));
+        return result;
+    }
+
+    public async Task AddAsync(SubtaskEntity entity, CancellationToken ct = default)
+    {
+        await using var conn = _factory.Open();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = """
+            INSERT INTO subtasks (id, task_id, title, completed, order_num, created_at)
+            VALUES (@id, @task_id, @title, @completed, @order_num, @created_at)
+            """;
+        BindSubtask(cmd, entity);
+        await cmd.ExecuteNonQueryAsync(ct);
+    }
+
+    public async Task UpdateAsync(SubtaskEntity entity, CancellationToken ct = default)
+    {
+        await using var conn = _factory.Open();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = """
+            UPDATE subtasks SET title = @title, completed = @completed, order_num = @order_num
+            WHERE id = @id
+            """;
+        cmd.Parameters.AddWithValue("@id", entity.Id);
+        cmd.Parameters.AddWithValue("@title", entity.Title);
+        cmd.Parameters.AddWithValue("@completed", entity.Completed ? 1 : 0);
+        cmd.Parameters.AddWithValue("@order_num", entity.OrderNum);
+        await cmd.ExecuteNonQueryAsync(ct);
+    }
+
+    public async Task DeleteAsync(string id, CancellationToken ct = default)
+    {
+        await using var conn = _factory.Open();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = "DELETE FROM subtasks WHERE id = @id";
+        cmd.Parameters.AddWithValue("@id", id);
+        await cmd.ExecuteNonQueryAsync(ct);
+    }
+
+    private static void BindSubtask(SqliteCommand cmd, SubtaskEntity e)
+    {
+        cmd.Parameters.AddWithValue("@id", e.Id);
+        cmd.Parameters.AddWithValue("@task_id", e.TaskId);
+        cmd.Parameters.AddWithValue("@title", e.Title);
+        cmd.Parameters.AddWithValue("@completed", e.Completed ? 1 : 0);
+        cmd.Parameters.AddWithValue("@order_num", e.OrderNum);
+        cmd.Parameters.AddWithValue("@created_at", e.CreatedAt.ToString("o"));
+    }
+
+    private static SubtaskEntity ReadSubtask(SqliteDataReader r) => new()
+    {
+        Id = r.GetString(0),
+        TaskId = r.GetString(1),
+        Title = r.GetString(2),
+        Completed = r.GetInt64(3) != 0,
+        OrderNum = r.GetInt32(4),
+        CreatedAt = DateTime.Parse(r.GetString(5)),
+    };
+}

src/ClaudeDo.Worker/Program.cs

@@ -19,6 +19,7 @@ builder.Services.AddSingleton(dbFactory);
 builder.Services.AddSingleton<TagRepository>();
 builder.Services.AddSingleton<ListRepository>();
 builder.Services.AddSingleton<TaskRepository>();
+builder.Services.AddSingleton<SubtaskRepository>();
 builder.Services.AddSingleton<WorktreeRepository>();
 builder.Services.AddSingleton<TaskRunRepository>();
 builder.Services.AddHostedService<StaleTaskRecovery>();

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -12,6 +12,7 @@ public sealed class TaskRunner
     private readonly TaskRunRepository _runRepo;
     private readonly ListRepository _listRepo;
     private readonly WorktreeRepository _wtRepo;
+    private readonly SubtaskRepository _subtaskRepo;
     private readonly HubBroadcaster _broadcaster;
     private readonly WorktreeManager _wtManager;
     private readonly ClaudeArgsBuilder _argsBuilder;
@@ -24,6 +25,7 @@ public sealed class TaskRunner
         TaskRunRepository runRepo,
         ListRepository listRepo,
         WorktreeRepository wtRepo,
+        SubtaskRepository subtaskRepo,
         HubBroadcaster broadcaster,
         WorktreeManager wtManager,
         ClaudeArgsBuilder argsBuilder,
@@ -35,6 +37,7 @@ public sealed class TaskRunner
         _runRepo = runRepo;
         _listRepo = listRepo;
         _wtRepo = wtRepo;
+        _subtaskRepo = subtaskRepo;
         _broadcaster = broadcaster;
         _wtManager = wtManager;
         _argsBuilder = argsBuilder;
@@ -91,9 +94,16 @@ public sealed class TaskRunner
             await _broadcaster.TaskStarted(slot, task.Id, now);
 
             // Build prompt.
-            var prompt = string.IsNullOrWhiteSpace(task.Description)
-                ? task.Title
-                : $"{task.Title}\n\n{task.Description.Trim()}";
+            var subtasks = await _subtaskRepo.GetByTaskIdAsync(task.Id, ct);
+            var sb = new System.Text.StringBuilder(task.Title);
+            if (!string.IsNullOrWhiteSpace(task.Description)) sb.Append("\n\n").Append(task.Description.Trim());
+            if (subtasks.Count > 0)
+            {
+                sb.Append("\n\n## Sub-Tasks\n");
+                foreach (var s in subtasks)
+                    sb.Append(s.Completed ? "- [x] " : "- [ ] ").Append(s.Title).Append('\n');
+            }
+            var prompt = sb.ToString();
 
             // Run 1.
             var result = await RunOnceAsync(task.Id, slot, runDir, resolvedConfig, 1, false, prompt, ct);