Extension data becomes a non-empty opaque bstr bounded by the frame of its
container; the base protocol never decodes or validates it. Arrays hold at
most 64 extensions, extension_version is bounded to 2^32-1 and the profile's
period and genesis_time to 2^53-1. The multiplicity exception is removed,
ERR_EXTENSION_DATA_INVALID is added, the §57 limits become MUST with an
explicit error mapping, §58 names the protocol's CBOR profile and §72 sets
the registration rules. §76 records the six reproducible cases behind the
change. The implementation follows in the next commit.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
