OptionalrevisionPositive integer revision of the channel key (default 1).
Revision N ≥ 2 derives a key that is independent of revision 1 for
the same context — rotate a compromised channel by bumping the
revision on both peers in lockstep.
Canonical by construction: NFKC normalization applies to the string
context only. Integers have no Unicode representation, so no
normalization is needed or performed on revision.
Options for Handle.deriveChannelKey.
All fields are optional; the defaults reproduce the frozen v1.0 derivation exactly (specs/v1.0.md §3).