secureVersion and the key only matter for the full 1536-byte request; the
older sizes always save without a key. Otherwise SDK 2.07+ uses the new
keyed hash for versions 0 and 3, older SDKs the old keyed hash for 0 and
no key for 3, and version 2 is always the old keyed hash.
Versions 0, 2 and 3 all require a key, and are rejected with SAVE_PARAM
otherwise - including 0, which we used to save without a key. Matches the
SFO modes and save errors recorded in utility/savedata/secureversion; what
remains there is load strictness when secureVersion doesn't match the
file, which we keep lenient for older saves.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
