diff --git a/src/ClaudeDo.Data/Git/GitService.cs b/src/ClaudeDo.Data/Git/GitService.cs
index e7f55d7..d736b71 100644
--- a/src/ClaudeDo.Data/Git/GitService.cs
+++ b/src/ClaudeDo.Data/Git/GitService.cs
@@ -183,6 +183,14 @@ public sealed class GitService
         return File.Exists(Path.Combine(gitDir, "MERGE_HEAD"));
     }
 
+    public async Task<(int ExitCode, string Stderr)> MergeNoFfAsync(
+        string repoDir, string sourceBranch, string message, CancellationToken ct = default)
+    {
+        var (exitCode, _, stderr) = await RunGitAsync(repoDir,
+            ["merge", "--no-ff", "-m", message, sourceBranch], ct);
+        return (exitCode, stderr);
+    }
+
     public async Task MergeFfOnlyAsync(string repoDir, string branchName, CancellationToken ct = default)
     {
         var (exitCode, _, stderr) = await RunGitAsync(repoDir, ["merge", "--ff-only", branchName], ct);
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/GitServiceMergeTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/GitServiceMergeTests.cs
index 0b04efb..bce82ed 100644
--- a/tests/ClaudeDo.Worker.Tests/Runner/GitServiceMergeTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Runner/GitServiceMergeTests.cs
@@ -72,4 +72,61 @@ public class GitServiceMergeTests : IDisposable
         var git = new GitService();
         Assert.True(await git.IsMidMergeAsync(repo.RepoDir));
     }
+
+    [Fact]
+    public async Task MergeNoFfAsync_DivergedNonConflicting_ReturnsZero_AndCreatesMergeCommit()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+
+        // Create a feature branch with one new file.
+        GitRepoFixture.RunGit(repo.RepoDir, "checkout", "-b", "feature/merge");
+        File.WriteAllText(Path.Combine(repo.RepoDir, "feature.txt"), "hello\n");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "feat: add feature.txt");
+
+        // Back to default and add a non-overlapping file so history diverges.
+        string defaultBranch;
+        try { defaultBranch = GitRepoFixture.RunGit(repo.RepoDir, "symbolic-ref", "--short", "refs/remotes/origin/HEAD").Trim().Replace("origin/", ""); }
+        catch { defaultBranch = "main"; }
+        if (string.IsNullOrEmpty(defaultBranch)) defaultBranch = "main";
+        try { GitRepoFixture.RunGit(repo.RepoDir, "checkout", defaultBranch); }
+        catch { GitRepoFixture.RunGit(repo.RepoDir, "checkout", "master"); defaultBranch = "master"; }
+        File.WriteAllText(Path.Combine(repo.RepoDir, "other.txt"), "other\n");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "chore: add other.txt");
+
+        var git = new GitService();
+        var (exitCode, stderr) = await git.MergeNoFfAsync(repo.RepoDir, "feature/merge", "Merge feature/merge");
+
+        Assert.Equal(0, exitCode);
+        // Confirm merge commit exists (two parents on HEAD).
+        var parents = GitRepoFixture.RunGit(repo.RepoDir, "rev-list", "--parents", "-n", "1", "HEAD").Trim();
+        Assert.True(parents.Split(' ').Length >= 3, $"Expected merge commit (3 tokens), got: '{parents}'");
+    }
+
+    [Fact]
+    public async Task MergeNoFfAsync_Conflict_ReturnsNonZero()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+
+        // Both branches modify README.md — guaranteed conflict.
+        GitRepoFixture.RunGit(repo.RepoDir, "checkout", "-b", "feature/conflict");
+        File.WriteAllText(Path.Combine(repo.RepoDir, "README.md"), "# feature side\n");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "feat: feature edit");
+
+        string defaultBranch = "main";
+        try { GitRepoFixture.RunGit(repo.RepoDir, "checkout", "main"); }
+        catch { GitRepoFixture.RunGit(repo.RepoDir, "checkout", "master"); defaultBranch = "master"; }
+        File.WriteAllText(Path.Combine(repo.RepoDir, "README.md"), "# main side\n");
+        GitRepoFixture.RunGit(repo.RepoDir, "add", "-A");
+        GitRepoFixture.RunGit(repo.RepoDir, "commit", "-m", "chore: main edit");
+
+        var git = new GitService();
+        var (exitCode, _) = await git.MergeNoFfAsync(repo.RepoDir, "feature/conflict", "merge");
+
+        Assert.NotEqual(0, exitCode);
+    }
 }