room-share: a join drops the notice entirely when the roster pushes the envelope over 4,000 units #1932

Implementation: FlyBot (ours) — PR follows within 24h. Do not pick up without a pickup-ok comment on this issue.

Written-by: FlyBot Lead
Claimed-by: FlyBot Lead
Claim-Id: 3de267c5d3ce4ca6b67dbfc09ed4db8a
Branch: dev/1-fitjoin-notice
Base: 77c9bc6
At: 2026-10-31T12:26:44Z

Implementation: FlyBot (ours) — PR follows within 24h. Do not pick up without a pickup-ok comment.

Written-by: FlyBot Lead

What. fitJoin in core/src/shared/room-share.js trims the notice before the roster, and it trims it by the envelope's total overflow (extra = wire().length - ROOM_SHARE_TEXT_MAX) instead of by the notice's own contribution. When the overflow comes from the roster, extra is far larger than the notice, so the notice is deleted outright — and the roster is popped afterwards anyway, so the deletion buys nothing.

Why it matters (user-visible). On the receiving side a join with notice present sets or clears the notice, and absent leaves it untouched (core/src/host/room-membership.js, noticeOf). So in any room whose roster pushes the envelope near 4,000 units, the guest never receives a notice update and never receives an explicit clear: the room keeps showing the old notice with no hint that anything was dropped.

Reproduction (live main 77c9bc66, pure encode→parse, no network). Roster rows are { name: 'Coder NN', handle: '@coderNN', home: '@hN.test', ownerName: 'O'.repeat(60) }:

An explicit empty notice — 0 characters of payload — is deleted, and the notice's own length has no bearing on the outcome.

Expected.

• The notice is trimmed only by its own contribution, and survives whenever it still fits after the roster is fitted.
• notice: '' is preserved (present and empty means "clear") and never dropped for space it does not use.
• Roster rows are display data: fit them by their own cost before deleting the notice.
• The envelope stays ≤ 4,000 units.

Acceptance (red first, assert on the parsed fields).

1. 29-row roster as above + notice: 'x' → parses back to 'x', wire ≤ 4000.
2. Same roster + notice: '' → parses back to '' (present and empty).
3. 26-row roster + 2000-character notice → still trimmed to ≤ 4000, and well formed (no half code point).
4. Mutation: revert the fix → 1 and 2 go red.

Scope. fitJoin in core/src/shared/room-share.js (about 6 lines) + one case in core/test/remote-room.test.js + the mirror patches/ds-bot/files/src/shared/room-share.js. This is not introduced by #1929 (fitJoin was untouched there); it is existing behaviour.

Not in this change. The fitTransport text loop and the code-point cut work from #1929 are already on main; do not re-touch them.

Dedupe: checked open issues — #1928 (body/history cut, closed by #1929) and #1930 (host prompt cuts) are the nearest; no open issue covers notice preservation in fitJoin.