The relay stopped storing them, so `createGroup` no longer sends one and
the `name` it returns is a placeholder. The real name is held in the
sealed vault and travels between members: on every group envelope, and as
an announcement riding the `delivery_key` control kind at creation and on
adding a member.
`delivery_key` rather than a new kind because a new one would arrive on
every phone running v5 as a bubble full of raw JSON.
An announced name is recorded as a CLAIM, not adopted. Conversations does
not know the rosters, and a name taken on the sender's word would let
anyone who can reach you write whatever they liked into your chat list
under a group heading you have no reason to doubt. Session checks it
against the relay's roster and only then stores it.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
