Salvaged from PR #83414 (4 commits squashed to final state) and composed
with the presentation-mention escape retry from PR #82646 already on this
branch: send() now resolves @Name tokens to channel-member pubkeys
(membership-accurate via `channels members`, TTL-cached, Unicode token
boundaries, ambiguous names stay presentation-only) and passes explicit
--mention args; recovery ladder handles membership drift, unresolvable
prose @tokens (escape retry, #78797), and a final self-mention downgrade.
a74080437a