fix: clean stale partial database backups

tests/test_db_backup_service.py

@@ -0,0 +1,41 @@
+import os
+import time
+
+
+def test_cleanup_partial_backups_removes_only_stale_zero_byte_files(tmp_path, monkeypatch):
+    from services import db_backup_service as backup
+
+    stale_zero = tmp_path / "momo_analytics_20260611_010050.sql.gz"
+    fresh_zero = tmp_path / "momo_analytics_20260618_134900.sql.gz"
+    normal_backup = tmp_path / "momo_analytics_20260618_020001.sql.gz"
+
+    stale_zero.write_bytes(b"")
+    fresh_zero.write_bytes(b"")
+    normal_backup.write_bytes(b"ok")
+
+    old_ts = time.time() - 7200
+    os.utime(stale_zero, (old_ts, old_ts))
+
+    monkeypatch.setattr(backup, "BACKUP_DIR", str(tmp_path))
+
+    deleted = backup.cleanup_partial_backups(min_age_minutes=60)
+
+    assert deleted == 1
+    assert not stale_zero.exists()
+    assert fresh_zero.exists()
+    assert normal_backup.exists()
+
+
+def test_cleanup_old_backups_counts_partial_cleanup(tmp_path, monkeypatch):
+    from services import db_backup_service as backup
+
+    stale_zero = tmp_path / "momo_analytics_20260611_010050.sql.gz"
+    stale_zero.write_bytes(b"")
+    old_ts = time.time() - 7200
+    os.utime(stale_zero, (old_ts, old_ts))
+
+    monkeypatch.setattr(backup, "BACKUP_DIR", str(tmp_path))
+    monkeypatch.setattr(backup, "RETENTION_DAYS", 7)
+
+    assert backup.cleanup_old_backups() == 1
+    assert not stale_zero.exists()