diff --git a/src/ClaudeDo.Worker/Refine/Interfaces/IRefineBroadcaster.cs b/src/ClaudeDo.Worker/Refine/Interfaces/IRefineBroadcaster.cs
new file mode 100644
index 0000000..e31cb29
--- /dev/null
+++ b/src/ClaudeDo.Worker/Refine/Interfaces/IRefineBroadcaster.cs
@@ -0,0 +1,7 @@
+namespace ClaudeDo.Worker.Refine;
+
+public interface IRefineBroadcaster
+{
+    Task RefineStartedAsync(string taskId);
+    Task RefineFinishedAsync(string taskId, bool success, string? error);
+}
diff --git a/src/ClaudeDo.Worker/Refine/Interfaces/IRefineRunner.cs b/src/ClaudeDo.Worker/Refine/Interfaces/IRefineRunner.cs
new file mode 100644
index 0000000..3f166ef
--- /dev/null
+++ b/src/ClaudeDo.Worker/Refine/Interfaces/IRefineRunner.cs
@@ -0,0 +1,8 @@
+namespace ClaudeDo.Worker.Refine;
+
+public interface IRefineRunner
+{
+    Task<RefineRunOutcome> RefineAsync(string taskId, CancellationToken ct);
+}
+
+public sealed record RefineRunOutcome(bool Success, string Message);
diff --git a/src/ClaudeDo.Worker/Refine/RefinePrompt.cs b/src/ClaudeDo.Worker/Refine/RefinePrompt.cs
new file mode 100644
index 0000000..6dc5401
--- /dev/null
+++ b/src/ClaudeDo.Worker/Refine/RefinePrompt.cs
@@ -0,0 +1,38 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+
+namespace ClaudeDo.Worker.Refine;
+
+public static class RefinePrompt
+{
+    public const string GetTaskTool = "mcp__claudedo__get_task";
+    public const string UpdateTaskTool = "mcp__claudedo__update_task";
+    public const string AddSubtaskTool = "mcp__claudedo__add_subtask";
+
+    public static string LogPath(string taskId) =>
+        System.IO.Path.Combine(Paths.AppDataRoot(), "logs", $"refine-{Short(taskId)}.log");
+
+    public static string BuildArgs(int maxTurns, bool canReadRepo)
+    {
+        var tools = canReadRepo
+            ? $"{GetTaskTool} {UpdateTaskTool} {AddSubtaskTool} Read Grep Glob"
+            : $"{GetTaskTool} {UpdateTaskTool} {AddSubtaskTool}";
+        return "-p --output-format stream-json --verbose --permission-mode acceptEdits " +
+               $"--max-turns {maxTurns} --allowedTools {tools}";
+    }
+
+    public static string BuildPrompt(TaskEntity task, IEnumerable<SubtaskEntity> subtasks)
+    {
+        var open = subtasks.Where(s => !s.Completed).Select(s => $"- {s.Title}").ToList();
+        var subText = open.Count == 0 ? "(none)" : string.Join("\n", open);
+        return PromptFiles.Render(PromptKind.Refine, new Dictionary<string, string>
+        {
+            ["taskId"] = task.Id,
+            ["title"] = task.Title,
+            ["description"] = string.IsNullOrWhiteSpace(task.Description) ? "(empty)" : task.Description!,
+            ["subtasks"] = subText,
+        });
+    }
+
+    private static string Short(string id) => id.Length >= 8 ? id[..8] : id;
+}
diff --git a/src/ClaudeDo.Worker/Refine/RefineRunner.cs b/src/ClaudeDo.Worker/Refine/RefineRunner.cs
new file mode 100644
index 0000000..14fdd1d
--- /dev/null
+++ b/src/ClaudeDo.Worker/Refine/RefineRunner.cs
@@ -0,0 +1,108 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Runner;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Refine;
+
+public sealed class RefineRunner : IRefineRunner
+{
+    private static readonly TimeSpan RunTimeout = TimeSpan.FromMinutes(5);
+    private const int MaxTurns = 25;
+
+    private readonly IClaudeProcess _claude;
+    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly ILogger<RefineRunner> _logger;
+    private readonly IRefineBroadcaster _broadcaster;
+
+    private readonly object _lock = new();
+    private readonly HashSet<string> _inFlight = new();
+
+    public RefineRunner(
+        IClaudeProcess claude,
+        IDbContextFactory<ClaudeDoDbContext> dbFactory,
+        ILogger<RefineRunner> logger,
+        IRefineBroadcaster broadcaster)
+    {
+        _claude = claude;
+        _dbFactory = dbFactory;
+        _logger = logger;
+        _broadcaster = broadcaster;
+    }
+
+    public async Task<RefineRunOutcome> RefineAsync(string taskId, CancellationToken ct)
+    {
+        lock (_lock)
+        {
+            if (!_inFlight.Add(taskId))
+                return new RefineRunOutcome(false, "Already refining this task");
+        }
+
+        var success = false;
+        string? error = null;
+        try
+        {
+            ClaudeDo.Data.Models.TaskEntity task;
+            List<ClaudeDo.Data.Models.SubtaskEntity> subs;
+            string? workingDir;
+            await using (var dbCtx = await _dbFactory.CreateDbContextAsync(ct))
+            {
+                var tasks = new TaskRepository(dbCtx);
+                task = await tasks.GetByIdAsync(taskId, ct)
+                    ?? throw new InvalidOperationException($"Task {taskId} not found.");
+                if (task.Status != TaskStatus.Idle)
+                    return new RefineRunOutcome(false, $"Task must be Idle to refine (is {task.Status}).");
+                subs = await new SubtaskRepository(dbCtx).GetByTaskIdAsync(taskId, ct);
+                var list = await new ListRepository(dbCtx).GetByIdAsync(task.ListId, ct);
+                workingDir = list?.WorkingDir;
+            }
+
+            var canReadRepo = !string.IsNullOrWhiteSpace(workingDir) && Directory.Exists(workingDir);
+            var cwd = canReadRepo ? workingDir! : Paths.AppDataRoot();
+            Directory.CreateDirectory(cwd);
+
+            var logPath = RefinePrompt.LogPath(taskId);
+            try { if (File.Exists(logPath)) File.Delete(logPath); } catch { }
+            await using var logWriter = new LogWriter(logPath);
+
+            await _broadcaster.RefineStartedAsync(taskId);
+
+            var prompt = RefinePrompt.BuildPrompt(task, subs);
+            var args = RefinePrompt.BuildArgs(MaxTurns, canReadRepo);
+
+            using var timeoutCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
+            timeoutCts.CancelAfter(RunTimeout);
+
+            var result = await _claude.RunAsync(
+                arguments: args,
+                prompt: prompt,
+                workingDirectory: cwd,
+                onStdoutLine: async line => await logWriter.WriteLineAsync(line),
+                ct: timeoutCts.Token);
+
+            success = result.IsSuccess;
+            if (!success) error = $"exit code {result.ExitCode}";
+            return success
+                ? new RefineRunOutcome(true, "Refine complete")
+                : new RefineRunOutcome(false, error!);
+        }
+        catch (OperationCanceledException) when (!ct.IsCancellationRequested)
+        {
+            error = $"timed out after {RunTimeout.TotalMinutes:0} min";
+            return new RefineRunOutcome(false, error);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Refine run failed for {TaskId}", taskId);
+            error = ex.Message;
+            return new RefineRunOutcome(false, ex.Message);
+        }
+        finally
+        {
+            await _broadcaster.RefineFinishedAsync(taskId, success, error);
+            lock (_lock) { _inFlight.Remove(taskId); }
+        }
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs b/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs
new file mode 100644
index 0000000..57e7027
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs
@@ -0,0 +1,52 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Worker.Refine;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.Refine;
+
+public sealed class RefinePromptTests
+{
+    [Fact]
+    public void BuildArgs_includes_read_tools_when_repo_available()
+    {
+        var args = RefinePrompt.BuildArgs(20, canReadRepo: true);
+
+        Assert.Contains("--permission-mode acceptEdits", args);
+        Assert.Contains("mcp__claudedo__add_subtask", args);
+        Assert.Contains(" Read Grep Glob", args);
+    }
+
+    [Fact]
+    public void BuildArgs_drops_read_tools_in_text_only_mode()
+    {
+        var args = RefinePrompt.BuildArgs(20, canReadRepo: false);
+
+        Assert.DoesNotContain("Glob", args);
+        Assert.Contains("mcp__claudedo__update_task", args);
+    }
+
+    [Fact]
+    public void BuildPrompt_seeds_task_fields_and_open_subtasks()
+    {
+        var task = new TaskEntity
+        {
+            Id = "abc12345",
+            ListId = "l",
+            Title = "T",
+            Description = "D",
+            Status = TaskStatus.Idle,
+            CreatedAt = DateTime.UtcNow,
+        };
+        var subtasks = new List<SubtaskEntity>
+        {
+            new() { Id = "s1", TaskId = "abc12345", Title = "open one", Completed = false, CreatedAt = DateTime.UtcNow },
+            new() { Id = "s2", TaskId = "abc12345", Title = "done one", Completed = true, CreatedAt = DateTime.UtcNow },
+        };
+
+        var prompt = RefinePrompt.BuildPrompt(task, subtasks);
+
+        Assert.Contains("abc12345", prompt);
+        Assert.Contains("open one", prompt);
+        Assert.DoesNotContain("done one", prompt);
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs b/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs
new file mode 100644
index 0000000..ed4b534
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs
@@ -0,0 +1,138 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Refine;
+using ClaudeDo.Worker.Runner;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using Microsoft.Extensions.Logging.Abstractions;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.Refine;
+
+public sealed class RefineRunnerTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly ClaudeDoDbContext _ctx;
+
+    public RefineRunnerTests()
+    {
+        _ctx = _db.CreateContext();
+    }
+
+    public void Dispose()
+    {
+        _ctx.Dispose();
+        _db.Dispose();
+    }
+
+    private async Task<string> SeedListAsync()
+    {
+        var listId = Guid.NewGuid().ToString();
+        await new ListRepository(_ctx).AddAsync(new ListEntity
+        {
+            Id = listId,
+            Name = "Test",
+            CreatedAt = DateTime.UtcNow,
+            WorkingDir = null,
+        });
+        return listId;
+    }
+
+    private async Task<TaskEntity> SeedTaskAsync(string listId, TaskStatus status)
+    {
+        var task = new TaskEntity
+        {
+            Id = Guid.NewGuid().ToString(),
+            ListId = listId,
+            Title = "Test task",
+            Status = status,
+            CreatedAt = DateTime.UtcNow,
+        };
+        await new TaskRepository(_ctx).AddAsync(task);
+        return task;
+    }
+
+    private RefineRunner BuildRunner(RecordingClaudeProcess claude, RecordingRefineBroadcaster broadcaster)
+    {
+        return new RefineRunner(
+            claude,
+            _db.CreateFactory(),
+            NullLogger<RefineRunner>.Instance,
+            broadcaster);
+    }
+
+    [Fact]
+    public async Task Refuses_when_task_not_idle()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId, TaskStatus.Queued);
+
+        var claude = new RecordingClaudeProcess(success: true);
+        var broadcaster = new RecordingRefineBroadcaster();
+        var runner = BuildRunner(claude, broadcaster);
+
+        var outcome = await runner.RefineAsync(task.Id, CancellationToken.None);
+
+        Assert.False(outcome.Success);
+        Assert.Equal(0, claude.CallCount);
+    }
+
+    [Fact]
+    public async Task Idle_task_invokes_claude_once_and_brackets_with_events()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId, TaskStatus.Idle);
+
+        var claude = new RecordingClaudeProcess(success: true);
+        var broadcaster = new RecordingRefineBroadcaster();
+        var runner = BuildRunner(claude, broadcaster);
+
+        var outcome = await runner.RefineAsync(task.Id, CancellationToken.None);
+
+        Assert.True(outcome.Success);
+        Assert.Equal(1, claude.CallCount);
+        Assert.Equal(1, broadcaster.StartedCount);
+        Assert.Equal(1, broadcaster.FinishedCount);
+    }
+}
+
+internal sealed class RecordingClaudeProcess : IClaudeProcess
+{
+    private readonly bool _success;
+    private int _callCount;
+
+    public int CallCount => _callCount;
+
+    public RecordingClaudeProcess(bool success) => _success = success;
+
+    public Task<RunResult> RunAsync(string arguments, string prompt, string workingDirectory,
+        Func<string, Task> onStdoutLine, CancellationToken ct)
+    {
+        Interlocked.Increment(ref _callCount);
+        var result = _success
+            ? new RunResult { ExitCode = 0, ResultMarkdown = "ok" }
+            : new RunResult { ExitCode = 1, ResultMarkdown = null };
+        return Task.FromResult(result);
+    }
+}
+
+internal sealed class RecordingRefineBroadcaster : IRefineBroadcaster
+{
+    private int _startedCount;
+    private int _finishedCount;
+
+    public int StartedCount => _startedCount;
+    public int FinishedCount => _finishedCount;
+
+    public Task RefineStartedAsync(string taskId)
+    {
+        Interlocked.Increment(ref _startedCount);
+        return Task.CompletedTask;
+    }
+
+    public Task RefineFinishedAsync(string taskId, bool success, string? error)
+    {
+        Interlocked.Increment(ref _finishedCount);
+        return Task.CompletedTask;
+    }
+}