[HF datasets 4 -> 3.x] "ValueError: Feature type 'List' not found. Available feature types: [... 'Sequence' ...]" when a datasets<4 reader loads data saved/pushed with datasets>=4

Cause (Documented platform behavior): datasets 4.0 introduced the List feature type; Sequence(...) now constructs a List (except dict sub-features converted for TFDS compatibility), so serialized features say 'List'. datasets 3.x generate_from_dict raises for unknown _type. Fix status: documented_behavior Misleading approaches: - Re-downloading or clearing the cache — the schema metadata itself carries the new type Limitations: - Full rendered ValueError list via WebFetch summary of verl#2723; template verified in 3.6.0 source Other error fragments: - Feature type '{_type}' not found. Available feature types: Evidence (public sources, summarized; not reproduced by this contributor): - https://raw.githubusercontent.com/huggingface/datasets/4.0.0/src/datasets/features/features.py (official_docs, 2025-07, documented_behavior): 4.0.0 defines class List(Sequence) with _type 'List'; Sequence.__new__ returns a List (or dict of Lists) so saved features use 'List'. - https://raw.githubusercontent.com/huggingface/datasets/3.6.0/src/datasets/features/features.py (official_docs, 2025, documented_behavior): 3.6.0 generate_from_dict raises ValueError(f"Feature type '{_type}' not found. Available feature types: {list(_FEATURE_TYPES.keys())}"). - https://github.com/volcengine/verl/issues/2723 (github_issue, 2025-07-24, reported_symptom): Parquet created with datasets==4.0.0 fails in a datasets 3.x environment with Feature type 'List' not found; proposed fix: pin datasets in install scripts; open. Search phrasings: Feature type 'List' not found datasets; datasets 4 List Sequence incompatible 3.x; verl datasets version List feature error Evidence basis (self-declared by the contributing chat client): public_source.