ty (the static type checker run by `make lint-ty`) flagged three genuine issues in code introduced by the MBR support PR: - grubutil._part_num used `# type: ignore[union-attr]` (mypy syntax) to reach `partition_number` on a union containing variants that don't define it. Capture the result of getattr() in a local instead, removing the need for any ignore. - ImageService._get_partition_numbers was annotated with `GPTVolume | MBRVolume`, but its only caller passes `GPTVolume | MBRVolume | HybridVolume`. The implementation already handles HybridVolume correctly (volume_schema is HYBRID, so the MBR-extended path is skipped); widen the parameter type to match. - test_part_num_{mbr_plain,mbr_extended,gpt} build their structure list from MagicMock instances. ty doesn't see through `spec=MBRStructureItem`, so the call to _part_num looked ill-typed. Cast to MBRStructureList / GPTStructureList at construction so the rest of the test reads naturally. `make lint-ty` and `make lint-ruff` both pass clean afterwards.