- StreamStore/RecordStore → Streamable/Recordable (stateless mixins) - Store is sole base class, no MRO ambiguity - H5Store/MmapStore/JsonlStore mix in both traits explicitly - segments_are_records declared per-subclass (H5/Jsonl=True, bin=False) - Add tests for dpo_tokenize, lazy jsonl, dual-mode H5, stream-only bin - Remove unused _to_tensor helper