Bounded compression outcomes. Writes record compressed, below_threshold,
not_smaller, or write_over_limit (serialized form exceeds the decompression
cap, stored raw — a capacity signal); reads record decompressed,
fallback_raw (a marked payload zstd rejected and handed through untouched),
or read_over_limit (decompression would exceed the cap; handed through
untouched — a corruption/integrity signal).
Bounded compression outcomes. Writes record compressed, below_threshold, not_smaller, or write_over_limit (serialized form exceeds the decompression cap, stored raw — a capacity signal); reads record decompressed, fallback_raw (a marked payload zstd rejected and handed through untouched), or read_over_limit (decompression would exceed the cap; handed through untouched — a corruption/integrity signal).