fix(tools): guard csv replace against newer fan records

tests/test_fans_csv.py

@@ -104,6 +104,29 @@ def test_import_default_force_and_replace():
             db.close()
 
 
+def test_replace_guard_for_newer_rows():
+    series = parse_fans_csv(CSV_TEXT)
+    with tempfile.TemporaryDirectory() as tmp:
+        db = Database(Path(tmp) / "app.db")
+        db.initialize()
+        try:
+            repo = Repository(db)
+            repo.upsert_up_stat("2026-02-01", 37754047, follower=2000, following=None, ok=True, captured_at=1)
+            try:
+                import_fans_series(db, series, replace=True)
+            except ValueError as exc:
+                assert "allow-lossy-replace" in str(exc)
+            else:
+                raise AssertionError("存在更新记录时应拒绝 --replace")
+            result = import_fans_series(
+                db, series, replace=True, allow_lossy_replace=True, dry_run=True
+            )
+            assert result["deleted"] == 1
+            assert repo.get_up_stat("2026-02-01", 37754047)["follower"] == 2000
+        finally:
+            db.close()
+
+
 def test_replace_dry_run_counts_only():
     series = parse_fans_csv(CSV_TEXT)
     with tempfile.TemporaryDirectory() as tmp:
@@ -124,6 +147,7 @@ def main_test():
     test_parse_csv()
     test_parse_rejects_bad_values()
     test_import_default_force_and_replace()
+    test_replace_guard_for_newer_rows()
     test_replace_dry_run_counts_only()
     print("OK: 粉丝 CSV 解析/导入/替换/幂等测试全部通过")