feat(worker): let review_task/merge_task leave conflicts in tree via MCP

src/ClaudeDo.Worker/External/ExternalMcpService.cs

@@ -19,7 +19,7 @@ namespace ClaudeDo.Worker.External;
 public sealed record TaskListDto(string Id, string Name, string? WorkingDir);
 public sealed record DeleteTaskResult(bool Deleted, string Id);
 public sealed record CancelTaskResult(bool Cancelled, string Id);
-public sealed record ReviewTaskResult(TaskDto Task, string? MergeStatus, IReadOnlyList<string> MergeConflicts, string? MergeMessage);
+public sealed record ReviewTaskResult(TaskDto Task, string? MergeStatus, IReadOnlyList<string> MergeConflicts, string? MergeMessage, string? RepoPath = null);
 public sealed record StatusValueDto(string Status, string Meaning);
 
 public sealed record TaskDto(
@@ -44,7 +44,8 @@ public sealed record TaskDiffDto(
     string Content, IReadOnlyList<string> Files, bool Truncated, int TotalBytes);
 
 public sealed record MergeTaskResultDto(
-    bool Merged, string? MergeCommit, IReadOnlyList<string> Conflicts);
+    bool Merged, string? MergeCommit, IReadOnlyList<string> Conflicts,
+    bool ConflictsInTree = false, string? RepoPath = null);
 
 public sealed record WorktreeListItemDto(
     string? TaskId, string Path, string Branch,
@@ -300,7 +301,10 @@ public sealed class ExternalMcpService
         "decision='approve' → review+merge, exactly like the UI's Approve: a childless task merges its worktree into " +
         "targetBranch (default: the repo's current branch) then goes Done; a task with children drives the unit merge " +
         "(parent worktree if active + each Done child in order); a task without an active worktree approves straight to Done. " +
-        "mergeStatus 'conflict' means the merge stopped on conflicts (files listed) — resolve them in the ClaudeDo UI. " +
+        "mergeStatus 'conflict' means the merge stopped on conflicts (files listed) — by default the merge is cleanly " +
+        "aborted and you resolve in the ClaudeDo UI; pass leaveConflictsInTree=true to instead leave the conflict " +
+        "markers in the working tree (repoPath in the result) so you can resolve them and call continue_merge, " +
+        "or abort_merge to cancel. " +
         "decision='reject_rerun' → Queued and re-runs, resuming the agent's session with your feedback as the next turn (feedback is required). " +
         "decision='reject_park' → Idle for manual editing (feedback ignored). " +
         "decision='cancel' → Cancelled. " +
@@ -310,14 +314,16 @@ public sealed class ExternalMcpService
         string decision,
         string? feedback = null,
         string? targetBranch = null,
+        bool leaveConflictsInTree = false,
         CancellationToken cancellationToken = default)
     {
-        _ = await _tasks.GetByIdAsync(taskId, cancellationToken)
+        var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
             ?? throw new InvalidOperationException($"Task {taskId} not found.");
 
         string? mergeStatus = null;
         IReadOnlyList<string> mergeConflicts = Array.Empty<string>();
         string? mergeMessage = null;
+        string? repoPath = null;
 
         if (decision.Trim().ToLowerInvariant() == "approve")
         {
@@ -333,18 +339,38 @@ public sealed class ExternalMcpService
                 var parentDone = (await _tasks.GetByIdAsync(taskId, cancellationToken))!.Status == TaskStatus.Done;
                 mergeStatus = parentDone ? TaskMergeService.StatusMerged : TaskMergeService.StatusConflict;
                 if (!parentDone)
-                    mergeMessage = "unit merge paused on a conflict — resolve and continue it in the ClaudeDo UI";
+                {
+                    var list = await _lists.GetByIdAsync(task.ListId, cancellationToken);
+                    repoPath = list?.WorkingDir;
+                    mergeMessage = "unit merge paused on a conflict — markers left in the working tree; " +
+                        "resolve them then call continue_merge with the parent task id, or abort_merge to cancel";
+                }
             }
             else
             {
-                var r = await _merge.ApproveAndMergeAsync(taskId, targetBranch ?? "", cancellationToken);
+                var r = await _merge.ApproveAndMergeAsync(taskId, targetBranch ?? "", leaveConflictsInTree, cancellationToken);
                 if (r.Status == TaskMergeService.StatusBlocked)
                     throw new InvalidOperationException(r.ErrorMessage ?? "approve failed");
                 mergeStatus = r.Status;
                 mergeConflicts = r.ConflictFiles;
-                mergeMessage = r.Status == TaskMergeService.StatusConflict
-                    ? "merge conflict — the task stays WaitingForReview; resolve it in the ClaudeDo UI"
-                    : r.ErrorMessage;
+                if (r.Status == TaskMergeService.StatusConflict)
+                {
+                    if (leaveConflictsInTree)
+                    {
+                        var list = await _lists.GetByIdAsync(task.ListId, cancellationToken);
+                        repoPath = list?.WorkingDir;
+                        mergeMessage = "merge conflict — markers left in the working tree; " +
+                            "resolve them then call continue_merge, or abort_merge to cancel";
+                    }
+                    else
+                    {
+                        mergeMessage = "merge conflict — the task stays WaitingForReview; resolve it in the ClaudeDo UI";
+                    }
+                }
+                else
+                {
+                    mergeMessage = r.ErrorMessage;
+                }
             }
         }
         else
@@ -364,7 +390,7 @@ public sealed class ExternalMcpService
 
         return new ReviewTaskResult(
             ToDto((await _tasks.GetByIdAsync(taskId, cancellationToken))!),
-            mergeStatus, mergeConflicts, mergeMessage);
+            mergeStatus, mergeConflicts, mergeMessage, repoPath);
     }
 
     [McpServerTool, Description("Immediately run a task in the override execution slot (bypasses the agent queue).")]
@@ -484,13 +510,17 @@ public sealed class ExternalMcpService
         "dryRun=true: validates preconditions only, does not perform the merge; merged=false in the result means 'not actually merged'. " +
         "allowWaitingForReview=true: also allows merging a task in WaitingForReview (default false, which only allows Done). " +
         "On success: merged=true, mergeCommit contains the new merge commit SHA. " +
-        "On conflict: the merge is cleanly aborted (no half-merged state left); merged=false and conflicts lists the affected files.")]
+        "On conflict: by default the merge is cleanly aborted (no half-merged state left); merged=false and conflicts lists the affected files. " +
+        "leaveConflictsInTree=true: on conflict the merge is NOT aborted — conflict markers are left in the working " +
+        "tree at repoPath (conflictsInTree=true in the result) so you can resolve them there and call continue_merge, " +
+        "or abort_merge to cancel.")]
     public async Task<MergeTaskResultDto> MergeTask(
         string taskId,
         string targetBranch = "main",
         bool noFf = true,
         bool dryRun = false,
         bool allowWaitingForReview = false,
+        bool leaveConflictsInTree = false,
         CancellationToken cancellationToken = default)
     {
         var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
@@ -517,7 +547,7 @@ public sealed class ExternalMcpService
 
         var commitMessage = $"Merge task branch for: {task.Title}";
         var result = await _merge.MergeAsync(
-            taskId, targetBranch, removeWorktree: false, commitMessage, cancellationToken);
+            taskId, targetBranch, removeWorktree: false, commitMessage, leaveConflictsInTree, cancellationToken);
 
         if (result.Status == TaskMergeService.StatusMerged)
         {
@@ -532,7 +562,10 @@ public sealed class ExternalMcpService
         }
 
         if (result.Status == TaskMergeService.StatusConflict)
-            return new MergeTaskResultDto(false, null, result.ConflictFiles);
+            return leaveConflictsInTree
+                ? new MergeTaskResultDto(false, null, result.ConflictFiles,
+                    ConflictsInTree: true, RepoPath: list?.WorkingDir)
+                : new MergeTaskResultDto(false, null, result.ConflictFiles);
 
         throw new InvalidOperationException(result.ErrorMessage ?? $"Merge blocked: {result.Status}");
     }

src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs

@@ -342,7 +342,11 @@ public sealed class TaskMergeService
         return new MergePreviewResult(PreviewClean, Array.Empty<string>(), count);
     }
 
-    public async Task<MergeResult> ApproveAndMergeAsync(string taskId, string targetBranch, CancellationToken ct)
+    public Task<MergeResult> ApproveAndMergeAsync(string taskId, string targetBranch, CancellationToken ct)
+        => ApproveAndMergeAsync(taskId, targetBranch, leaveConflictsInTree: false, ct);
+
+    public async Task<MergeResult> ApproveAndMergeAsync(
+        string taskId, string targetBranch, bool leaveConflictsInTree, CancellationToken ct)
     {
         var (task, list, wt) = await LoadMergeContextAsync(taskId, ct);
 
@@ -367,7 +371,7 @@ public sealed class TaskMergeService
         // MergeAsync transitions the task WaitingForReview -> Done on a successful merge.
         // Remove the worktree on approve (matching the unit-merge path) so merged
         // worktrees don't pile up; the merge commit on the target branch is the record.
-        return await MergeAsync(taskId, target, removeWorktree: true, $"Merge {wt.BranchName}", ct);
+        return await MergeAsync(taskId, target, removeWorktree: true, $"Merge {wt.BranchName}", leaveConflictsInTree, ct);
     }
 
     private static MergeResult Blocked(string reason) =>

tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs

@@ -216,7 +216,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var task = await SeedTaskAsync(listId, status: TaskStatus.WaitingForReview);
         var sut = BuildSut(CreateQueue());
 
-        var result = await sut.ReviewTask(task.Id, "approve", null, null, CancellationToken.None);
+        var result = await sut.ReviewTask(task.Id, "approve", null, null, cancellationToken: CancellationToken.None);
 
         Assert.Equal("Done", result.Task.Status);
         Assert.Equal(TaskMergeService.StatusMerged, result.MergeStatus);
@@ -230,7 +230,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var sut = BuildSut(CreateQueue());
 
         await Assert.ThrowsAsync<InvalidOperationException>(() =>
-            sut.ReviewTask(task.Id, "reject_rerun", null, null, CancellationToken.None));
+            sut.ReviewTask(task.Id, "reject_rerun", null, null, cancellationToken: CancellationToken.None));
     }
 
     [Fact]
@@ -240,7 +240,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var task = await SeedTaskAsync(listId, status: TaskStatus.WaitingForReview);
         var sut = BuildSut(CreateQueue());
 
-        var result = await sut.ReviewTask(task.Id, "reject_rerun", "fix it", null, CancellationToken.None);
+        var result = await sut.ReviewTask(task.Id, "reject_rerun", "fix it", null, cancellationToken: CancellationToken.None);
 
         Assert.Equal("Queued", result.Task.Status);
         var loaded = await new TaskRepository(_db.CreateContext()).GetByIdAsync(task.Id);
@@ -255,7 +255,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var sut = BuildSut(CreateQueue());
 
         await Assert.ThrowsAsync<InvalidOperationException>(() =>
-            sut.ReviewTask(task.Id, "bogus", null, null, CancellationToken.None));
+            sut.ReviewTask(task.Id, "bogus", null, null, cancellationToken: CancellationToken.None));
     }
 
     [Fact]
@@ -275,7 +275,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         }
 
         var sut = BuildSut(CreateQueue());
-        var result = await sut.ReviewTask(task.Id, "approve", null, null, CancellationToken.None);
+        var result = await sut.ReviewTask(task.Id, "approve", null, null, cancellationToken: CancellationToken.None);
 
         Assert.Equal(TaskMergeService.StatusMerged, result.MergeStatus);
         Assert.Equal("Done", result.Task.Status);
@@ -321,7 +321,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         }
 
         var sut = BuildSut(CreateQueue());
-        var result = await sut.ReviewTask(parentId, "approve", null, "main", CancellationToken.None);
+        var result = await sut.ReviewTask(parentId, "approve", null, "main", cancellationToken: CancellationToken.None);
 
         Assert.Equal(TaskMergeService.StatusMerged, result.MergeStatus);
         Assert.Equal("Done", result.Task.Status);
@@ -610,7 +610,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var sut = BuildSut(CreateQueue());
 
         var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-            () => sut.MergeTask(task.Id, "main", true, false, false, CancellationToken.None));
+            () => sut.MergeTask(task.Id, "main", true, false, false, cancellationToken: CancellationToken.None));
         Assert.Contains("Done", ex.Message);
     }
 
@@ -785,7 +785,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var sut = BuildSut(CreateQueue());
 
         var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-            () => sut.MergeTask(task.Id, "main", true, false, false, CancellationToken.None));
+            () => sut.MergeTask(task.Id, "main", true, false, false, cancellationToken: CancellationToken.None));
         Assert.Contains("Done", ex.Message);
     }
 
@@ -797,7 +797,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var (task, _, _) = await SeedWorktreeAsync(TaskStatus.WaitingForReview);
         var sut = BuildSut(CreateQueue());
 
-        var result = await sut.MergeTask(task.Id, "main", true, dryRun: true, allowWaitingForReview: true, CancellationToken.None);
+        var result = await sut.MergeTask(task.Id, "main", true, dryRun: true, allowWaitingForReview: true, cancellationToken: CancellationToken.None);
 
         Assert.False(result.Merged);
         Assert.Null(result.MergeCommit);
@@ -817,13 +817,114 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var target = await new GitService().GetCurrentBranchAsync(list.WorkingDir, CancellationToken.None);
         var sut = BuildSut(CreateQueue());
 
-        var result = await sut.MergeTask(task.Id, target, true, dryRun: false, allowWaitingForReview: true, CancellationToken.None);
+        var result = await sut.MergeTask(task.Id, target, true, dryRun: false, allowWaitingForReview: true, cancellationToken: CancellationToken.None);
 
         Assert.True(result.Merged);
         var reloaded = await new TaskRepository(_db.CreateContext()).GetByIdAsync(task.Id);
         Assert.Equal(TaskStatus.Done, reloaded!.Status);
     }
 
+    // ── leaveConflictsInTree ──────────────────────────────────────────────────
+
+    private async Task<(TaskEntity task, ListEntity list, WorktreeContext wt)> SeedConflictingWorktreeAsync(
+        TaskStatus status = TaskStatus.WaitingForReview)
+    {
+        var (task, list, wt) = await SeedWorktreeAsync(status);
+
+        File.WriteAllText(Path.Combine(wt.WorktreePath, "README.md"), "# from worktree\n");
+        GitRepoFixture.RunGit(wt.WorktreePath, "add", "README.md");
+        GitRepoFixture.RunGit(wt.WorktreePath, "commit", "-m", "worktree edit");
+
+        File.WriteAllText(Path.Combine(list.WorkingDir!, "README.md"), "# from main\n");
+        GitRepoFixture.RunGit(list.WorkingDir!, "add", "README.md");
+        GitRepoFixture.RunGit(list.WorkingDir!, "commit", "-m", "main edit");
+
+        return (task, list, wt);
+    }
+
+    [Fact]
+    public async Task MergeTask_LeaveConflictsInTree_LeavesMarkersAndKeepsRepoMidMerge()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var (task, list, _) = await SeedConflictingWorktreeAsync(TaskStatus.WaitingForReview);
+        var target = await new GitService().GetCurrentBranchAsync(list.WorkingDir!);
+        var sut = BuildSut(CreateQueue());
+
+        var result = await sut.MergeTask(task.Id, target, true, dryRun: false,
+            allowWaitingForReview: true, leaveConflictsInTree: true, CancellationToken.None);
+
+        Assert.False(result.Merged);
+        Assert.True(result.ConflictsInTree);
+        Assert.Equal(list.WorkingDir, result.RepoPath);
+        Assert.Contains("README.md", result.Conflicts);
+        Assert.Contains("<<<<<<<", File.ReadAllText(Path.Combine(list.WorkingDir!, "README.md")));
+        Assert.True(await new GitService().IsMidMergeAsync(list.WorkingDir!));
+        var reloaded = await new TaskRepository(_db.CreateContext()).GetByIdAsync(task.Id);
+        Assert.Equal(TaskStatus.WaitingForReview, reloaded!.Status);
+
+        GitRepoFixture.RunGit(list.WorkingDir!, "merge", "--abort");
+    }
+
+    [Fact]
+    public async Task MergeTask_ConflictWithoutLeaveFlag_AbortsCleanly()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var (task, list, _) = await SeedConflictingWorktreeAsync(TaskStatus.WaitingForReview);
+        var target = await new GitService().GetCurrentBranchAsync(list.WorkingDir!);
+        var sut = BuildSut(CreateQueue());
+
+        var result = await sut.MergeTask(task.Id, target, true, dryRun: false,
+            allowWaitingForReview: true, leaveConflictsInTree: false, CancellationToken.None);
+
+        Assert.False(result.Merged);
+        Assert.False(result.ConflictsInTree);
+        Assert.Null(result.RepoPath);
+        Assert.Contains("README.md", result.Conflicts);
+        Assert.DoesNotContain("<<<<<<<", File.ReadAllText(Path.Combine(list.WorkingDir!, "README.md")));
+        Assert.False(await new GitService().IsMidMergeAsync(list.WorkingDir!));
+    }
+
+    [Fact]
+    public async Task ReviewTask_Approve_LeaveConflictsInTree_LeavesMarkersAndReportsRepoPath()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var (task, list, _) = await SeedConflictingWorktreeAsync(TaskStatus.WaitingForReview);
+        var sut = BuildSut(CreateQueue());
+
+        var result = await sut.ReviewTask(task.Id, "approve", null, null,
+            leaveConflictsInTree: true, CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusConflict, result.MergeStatus);
+        Assert.Equal(list.WorkingDir, result.RepoPath);
+        Assert.Contains("continue_merge", result.MergeMessage);
+        Assert.Contains("<<<<<<<", File.ReadAllText(Path.Combine(list.WorkingDir!, "README.md")));
+        Assert.True(await new GitService().IsMidMergeAsync(list.WorkingDir!));
+        Assert.Equal("WaitingForReview", result.Task.Status);
+
+        GitRepoFixture.RunGit(list.WorkingDir!, "merge", "--abort");
+    }
+
+    [Fact]
+    public async Task ReviewTask_Approve_ConflictWithoutLeaveFlag_KeepsOldBehaviour()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var (task, list, _) = await SeedConflictingWorktreeAsync(TaskStatus.WaitingForReview);
+        var sut = BuildSut(CreateQueue());
+
+        var result = await sut.ReviewTask(task.Id, "approve", null, null, cancellationToken: CancellationToken.None);
+
+        Assert.Equal(TaskMergeService.StatusConflict, result.MergeStatus);
+        Assert.Null(result.RepoPath);
+        Assert.Contains("ClaudeDo UI", result.MergeMessage);
+        Assert.DoesNotContain("<<<<<<<", File.ReadAllText(Path.Combine(list.WorkingDir!, "README.md")));
+        Assert.False(await new GitService().IsMidMergeAsync(list.WorkingDir!));
+        Assert.Equal("WaitingForReview", result.Task.Status);
+    }
+
     // ── AddTask model override ────────────────────────────────────────────────
 
     [Fact]