Branch menu (list/switch) for macOS+iOS shared chat via sessions.branches.*;
rewind/fork/switch gated on run activity and pending outbox work through a
durable session-mutation lease; outbox rows carry branch-epoch ownership with
local-only flush checks, atomic confirm/park transitions, attempt-versioned
delivery callbacks, fresh retry identity for possibly-accepted rows, and
epoch-guarded branch evidence; 21-locale native translations for new strings.