feat(git): add IsMidMergeAsync

src/ClaudeDo.Data/Git/GitService.cs

@@ -173,6 +173,16 @@ public sealed class GitService
             .ToList();
     }
 
+    public async Task<bool> IsMidMergeAsync(string repoDir, CancellationToken ct = default)
+    {
+        var (exitCode, stdout, _) = await RunGitAsync(repoDir, ["rev-parse", "--git-dir"], ct);
+        if (exitCode != 0) return false;
+        var gitDir = stdout.Trim();
+        if (!Path.IsPathRooted(gitDir))
+            gitDir = Path.Combine(repoDir, gitDir);
+        return File.Exists(Path.Combine(gitDir, "MERGE_HEAD"));
+    }
+
     public async Task MergeFfOnlyAsync(string repoDir, string branchName, CancellationToken ct = default)
     {
         var (exitCode, _, stderr) = await RunGitAsync(repoDir, ["merge", "--ff-only", branchName], ct);

tests/ClaudeDo.Worker.Tests/Runner/GitServiceMergeTests.cs

@@ -49,4 +49,27 @@ public class GitServiceMergeTests : IDisposable
         Assert.Contains("feature/x", branches);
         Assert.True(branches.Any(b => b == "main" || b == "master"));
     }
+
+    [Fact]
+    public async Task IsMidMergeAsync_FreshRepo_ReturnsFalse()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        var git = new GitService();
+
+        Assert.False(await git.IsMidMergeAsync(repo.RepoDir));
+    }
+
+    [Fact]
+    public async Task IsMidMergeAsync_MergeHeadPresent_ReturnsTrue()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        // Simulate a mid-merge state by dropping a MERGE_HEAD file.
+        var mergeHead = Path.Combine(repo.RepoDir, ".git", "MERGE_HEAD");
+        File.WriteAllText(mergeHead, "0000000000000000000000000000000000000000\n");
+
+        var git = new GitService();
+        Assert.True(await git.IsMidMergeAsync(repo.RepoDir));
+    }
 }