Ported from the pre-TSX PR onto the current module layout. main's
group-chat-view.tsx already restores the composer draft when
sendToGroupChat returns null (feat(desktop): retain Bot group drafts by
room, b42d8279ed), so the draft-loss half of the original fix is
FIXED_ON_MAIN and not re-applied here. What remained: sendToGroupChat in
group-rounds.ts still folded "no text" and "no members" into one silent
`return null`, so a fully typed message into a room whose roster had not
hydrated (or a legacy room record without member descriptors) was
rejected with no thread, no log entry and no error.
The guards are split: empty content stays silent, an empty member seat
raises host.notify with a Bot Mode i18n string (en/ja/zh/zh-hant). The
wording no longer promises a retry will help (review: a legacy room with
no member descriptors never recovers by retrying) and points at the two
real remedies.
The original source-regex .mjs tests are dropped per review; the
contract is pinned by a behavioural vitest in group-rounds.test.ts that
drives sendToGroupChat through the scripted room harness: empty members
→ null + one error toast + no log entry; blank text → null, no toast.
9c689bee1a