Compatibility contract

Version 0.1 readers reject unknown layout and record versions. A compatible change may add optional JSON keys that existing readers can ignore. Changing required meanings, tensor mapping, ordinal semantics, or supported codec identifiers requires a new layout version.

The earlier split-based 0.1 prototype is not supported. If a reader finds its sds.json root, it returns a specific unsupported-format error. Republish those records as one ordered 0.1 dataset; the library does not parse or adapt the prototype layout.

Variable shapes and optional fields are valid across records. Consumers decide whether records can form a batch.