pub const CODE_JOIN_V2_PREFIX: &str = "v2-";Expand description
huddle 2.2 (audit PA-1): the marker a v2 owner prepends to every join code it
issues. This is the out-of-band capability anchor that defeats a relay
downgrade: the owner hands the joiner the code over a channel the relay does
not control (Signal, in person, a QR), so the relay cannot strip this marker
the way it can strip a capabilities field from a network announcement. A
joiner that sees the marker sends the proof form unconditionally — it
never consults the relay-mediated capability for the code-join decision — so
the relay can no longer force the cleartext fallback. The marker begins with
a lowercase letter, which the join-code alphabet (ABCDEFGHJKMNPQRSTUVWXYZ23456789,
uppercase-only) never produces, so a legacy code can never be mistaken for a
v2 one. The proof is computed over the FULL code string, marker included.