Skip reviews of snapshots with no diff

internal/agents/review.go

@@ -108,6 +108,10 @@ func (m *Manager) startReviewer(ctx context.Context, task api.Task, snap api.Sna
 	if err != nil {
 		return err
 	}
+	if prompt == "" {
+		slog.Info("review skipped, snapshot has no diff", "task", task.Id, "snapshot", snap.N)
+		return nil
+	}
 
 	reviewID := store.NewID()
 	dir := m.reviewDir(project.Id, reviewID)
@@ -177,6 +181,9 @@ func (m *Manager) reviewPrompt(ctx context.Context, task api.Task, project api.P
 	if err != nil {
 		return "", err
 	}
+	if len(changes.Files) == 0 {
+		return "", nil
+	}
 	whole, err := git.Compare(project.RepoPath, project.DefaultBranch, snap.CommitSha, snap.TreeSha, "")
 	if err != nil {
 		return "", err