Reusable record and migration¶
The exact-length little-endian record contains an eight-byte product identity,
a nonzero u32 schema version, a u32 field count, then u32 stable-ID/f32 physical
value pairs. Its length is 16 + 8*N. Decoding accepts any field order but rejects
unknown or duplicate IDs, unexpected versions, incorrect counts, invalid values,
truncation and trailing data. Encoding validates destination length and version
before writing anything. It performs no stream I/O or allocation.
Products explicitly select a known old version and its schema before decoding.
migrate then matches stable IDs to a target schema: additions use defaults,
removals are dropped, and existing values must satisfy the target range. Unit
changes, ID renames and other semantic transformations require product-specific
migration code. Product identity and version selection belong to the consumer;
there is no automatic version registry, preset discovery or editor-state format.