diff --git a/src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs b/src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs
index 18db0bd..e8e578a 100644
--- a/src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs
+++ b/src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs
@@ -3,6 +3,7 @@ using ClaudeDo.Data.Git;
 using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.State;
 using Microsoft.EntityFrameworkCore;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -17,6 +18,11 @@ public sealed record MergeTargets(
     string DefaultBranch,
     IReadOnlyList<string> LocalBranches);
 
+public sealed record MergePreviewResult(
+    string Status,
+    IReadOnlyList<string> ConflictFiles,
+    int ChangedFileCount);
+
 public sealed class TaskMergeService
 {
     public const string StatusMerged   = "merged";
@@ -24,20 +30,27 @@ public sealed class TaskMergeService
     public const string StatusBlocked  = "blocked";
     public const string StatusAborted  = "aborted";
 
+    public const string PreviewClean       = "clean";
+    public const string PreviewConflict    = "conflict";
+    public const string PreviewUnavailable = "unavailable";
+
     private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
     private readonly GitService _git;
     private readonly HubBroadcaster _broadcaster;
+    private readonly ITaskStateService _state;
     private readonly ILogger<TaskMergeService> _logger;
 
     public TaskMergeService(
         IDbContextFactory<ClaudeDoDbContext> dbFactory,
         GitService git,
         HubBroadcaster broadcaster,
+        ITaskStateService state,
         ILogger<TaskMergeService> logger)
     {
         _dbFactory = dbFactory;
         _git = git;
         _broadcaster = broadcaster;
+        _state = state;
         _logger = logger;
     }
 
@@ -216,6 +229,56 @@ public sealed class TaskMergeService
         return new MergeTargets(current, branches);
     }
 
+    public async Task<MergePreviewResult> PreviewAsync(string taskId, string targetBranch, CancellationToken ct)
+    {
+        var (_, list, wt) = await LoadMergeContextAsync(taskId, ct);
+
+        if (wt is null || wt.State != WorktreeState.Active)
+            return new MergePreviewResult(PreviewUnavailable, Array.Empty<string>(), 0);
+        if (string.IsNullOrWhiteSpace(list.WorkingDir) || !await _git.IsGitRepoAsync(list.WorkingDir, ct))
+            return new MergePreviewResult(PreviewUnavailable, Array.Empty<string>(), 0);
+
+        var target = string.IsNullOrWhiteSpace(targetBranch)
+            ? await _git.GetCurrentBranchAsync(list.WorkingDir, ct)
+            : targetBranch;
+
+        var preview = await _git.PreviewMergeAsync(list.WorkingDir, target, wt.BranchName, ct);
+        if (!preview.Supported)
+            return new MergePreviewResult(PreviewUnavailable, Array.Empty<string>(), 0);
+        if (!preview.Clean)
+            return new MergePreviewResult(PreviewConflict, preview.ConflictFiles, 0);
+
+        var count = await _git.CountChangedFilesAsync(list.WorkingDir, target, wt.BranchName, ct);
+        return new MergePreviewResult(PreviewClean, Array.Empty<string>(), count);
+    }
+
+    public async Task<MergeResult> ApproveAndMergeAsync(string taskId, string targetBranch, CancellationToken ct)
+    {
+        var (task, list, wt) = await LoadMergeContextAsync(taskId, ct);
+
+        if (task.Status != TaskStatus.WaitingForReview)
+            return Blocked("task is not waiting for review");
+
+        if (wt is null || wt.State != WorktreeState.Active)
+        {
+            var done = await _state.ApproveReviewAsync(taskId, ct);
+            return done.Ok
+                ? new MergeResult(StatusMerged, Array.Empty<string>(), null)
+                : Blocked(done.Reason ?? "approve failed");
+        }
+
+        var target = string.IsNullOrWhiteSpace(targetBranch)
+            ? await _git.GetCurrentBranchAsync(list.WorkingDir, ct)
+            : targetBranch;
+
+        var merge = await MergeAsync(taskId, target, removeWorktree: false, $"Merge {wt.BranchName}", ct);
+        if (merge.Status != StatusMerged)
+            return merge;
+
+        var approve = await _state.ApproveReviewAsync(taskId, ct);
+        return approve.Ok ? merge : Blocked(approve.Reason ?? "approve failed");
+    }
+
     private static MergeResult Blocked(string reason) =>
         new(StatusBlocked, Array.Empty<string>(), reason);
 }
diff --git a/tests/ClaudeDo.Worker.Tests/Services/TaskMergeServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Services/TaskMergeServiceTests.cs
index 5efbea5..ac5ddd8 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/TaskMergeServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/TaskMergeServiceTests.cs
@@ -34,10 +34,12 @@ public class TaskMergeServiceTests : IDisposable
     {
         var fakeHub = new MergeRecordingHubContext();
         var broadcaster = new HubBroadcaster(fakeHub);
+        var state = TaskStateServiceBuilder.Build(db.CreateFactory()).State;
         var svc = new TaskMergeService(
             db.CreateFactory(),
             new GitService(),
             broadcaster,
+            state,
             NullLogger<TaskMergeService>.Instance);
         return (svc, fakeHub.Proxy);
     }
@@ -442,6 +444,146 @@ public class TaskMergeServiceTests : IDisposable
         Assert.Equal(WorktreeState.Active, wt.State);
     }
 
+    [Fact]
+    public async Task PreviewAsync_CleanWorktree_ReturnsClean()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        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"), "x\n");
+        await wtMgr.CommitIfChangedAsync(wtCtx, task, list, CancellationToken.None);
+
+        var (svc, _) = BuildService(db);
+        var target = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+
+        var preview = await svc.PreviewAsync(task.Id, target, CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.PreviewClean, preview.Status);
+        Assert.True(preview.ChangedFileCount >= 1);
+    }
+
+    [Fact]
+    public async Task PreviewAsync_Conflict_ReturnsConflictFiles()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        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, "README.md"), "# from worktree\n");
+        await wtMgr.CommitIfChangedAsync(wtCtx, task, list, CancellationToken.None);
+
+        File.WriteAllText(Path.Combine(repo.RepoDir, "README.md"), "# from main\n");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "main edit");
+
+        var (svc, _) = BuildService(db);
+        var target = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+
+        var preview = await svc.PreviewAsync(task.Id, target, CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.PreviewConflict, preview.Status);
+        Assert.Contains("README.md", preview.ConflictFiles);
+    }
+
+    [Fact]
+    public async Task PreviewAsync_NoActiveWorktree_ReturnsUnavailable()
+    {
+        var db = NewDb();
+        var (_, task) = await SeedListAndTask(db, workingDir: "/tmp", status: TaskStatus.WaitingForReview);
+        var (svc, _) = BuildService(db);
+
+        var preview = await svc.PreviewAsync(task.Id, "main", CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.PreviewUnavailable, preview.Status);
+    }
+
+    [Fact]
+    public async Task ApproveAndMergeAsync_CleanWorktree_MergesAndMarksDone()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        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 target = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+
+        var result = await svc.ApproveAndMergeAsync(task.Id, target, CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusMerged, result.Status);
+        using var ctx = db.CreateContext();
+        var updated = await new TaskRepository(ctx).GetByIdAsync(task.Id);
+        Assert.Equal(TaskStatus.Done, updated!.Status);
+        var wt = await new WorktreeRepository(ctx).GetByTaskIdAsync(task.Id);
+        Assert.Equal(WorktreeState.Merged, wt!.State);
+    }
+
+    [Fact]
+    public async Task ApproveAndMergeAsync_Conflict_LeavesTaskWaitingForReview()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        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, "README.md"), "# from worktree\n");
+        await wtMgr.CommitIfChangedAsync(wtCtx, task, list, CancellationToken.None);
+
+        File.WriteAllText(Path.Combine(repo.RepoDir, "README.md"), "# from main\n");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "main edit");
+        var headBefore = GitRepoFixture.RunGit(repo.RepoDir, "rev-parse", "HEAD").Trim();
+
+        var (svc, _) = BuildService(db);
+        var target = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+
+        var result = await svc.ApproveAndMergeAsync(task.Id, target, CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusConflict, result.Status);
+        Assert.Contains("README.md", result.ConflictFiles);
+
+        using var ctx = db.CreateContext();
+        var updated = await new TaskRepository(ctx).GetByIdAsync(task.Id);
+        Assert.Equal(TaskStatus.WaitingForReview, updated!.Status);
+        var wt = await new WorktreeRepository(ctx).GetByTaskIdAsync(task.Id);
+        Assert.Equal(WorktreeState.Active, wt!.State);
+        Assert.Equal(headBefore, GitRepoFixture.RunGit(repo.RepoDir, "rev-parse", "HEAD").Trim());
+        Assert.False(await new GitService().IsMidMergeAsync(repo.RepoDir));
+    }
+
+    [Fact]
+    public async Task ApproveAndMergeAsync_NoWorktree_MarksDone()
+    {
+        var db = NewDb();
+        var (_, task) = await SeedListAndTask(db, workingDir: "/tmp", status: TaskStatus.WaitingForReview);
+        var (svc, _) = BuildService(db);
+
+        var result = await svc.ApproveAndMergeAsync(task.Id, "main", CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusMerged, result.Status);
+        using var ctx = db.CreateContext();
+        var updated = await new TaskRepository(ctx).GetByIdAsync(task.Id);
+        Assert.Equal(TaskStatus.Done, updated!.Status);
+    }
+
     [Fact]
     public async Task MergeAsync_LeaveConflicts_DoesNotAbortAndReturnsConflictFiles()
     {