host: an unnamed group's name and Session title do not follow its seats (guest joins or leaves, and a group created with guests) #1995

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: 0607b85d322f4afe8b7c25feed09e93d
Branch: dev/3-p317-p319-unnamed-title-follows-seats
Base: 42b638c
At: 2026-11-01T06:34:58Z

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

An unnamed group's name is computed from its seats, but two paths leave the name (and the Session title) behind the seats: a guest joining or leaving an existing unnamed group, and a group created with guests already in it. Both leave a name the user sees that does not match who is in the room, and neither self-heals on restart.

A. Seat changes do not move the name

core/src/host/room-membership.js writes the roster through syncMembers in several places, but only some of them recompute room.name — none of the five seat paths below does, and none calls rt.retitleRoom. So after a guest joins an unnamed group the name still lists the old seats; after one leaves it still names the guest.

Landing points: invite :752, remove :803, ticket seat :1790, a remote seat reporting it left :1995, evictUnshared withdrawing a grant :2273.

Other syncMembers call sites must not recompute: inbound mirrors take their name from the share envelope, face rooms have their own formatFaceRoomTitle, and applyParticipants is not a seat change. A room with named: true, an inbound-share room and a face room return early.

B. A group created with guests is titled by the narrow formula

core/src/host/roster.js:327 computes const title = custom || autoRoomName(members) — without the room — and :330 creates the Session with it; :346-352 then rewrites state.rooms[id].name to autoRoomName(members, room) (the wide formula, which names the local user and keeps remote guests) but never retitles the Session. Two names diverge at creation and stay diverged: a restart does not repair them, because the stale check in store.js compares room.name to the formula and room.name is already correct (#1976/#1977).

Expected

The name the user sees follows the seats, on both paths, and the Session title moves with it.

• Use the same wide formula, autoRoomName(room.members, room) — do not introduce a second naming rule.
• Compute before await rt.save(), write room.name, call rt.retitleRoom(room), and only when the value actually changed (a no-op seat change must send no rename).
• A named room is never renamed; a room created without guests is renamed once, not twice.

Red first (each on its own)

On live main 42b638c2, in core/test/remote-room.test.js, four cases red and one control group green:

1. a guest who joins an unnamed group moves the name and the Session title;
2. a guest who leaves an unnamed group drops out of both;
3. a group created with a guest is titled by the formula that sees the room;
4. an unnamed group without guests is renamed once per seat change.

Control (must stay green on the unfixed tree): a named: true room keeps its name through an invite and a removal with zero renames; a Bot rename does not move the room name; the #1976 restart migration.

Matrix required in the PR: revert only the roster.js line → only case 3 red; revert only the five settleRoomName calls → cases 1/2/4 red and 3 green.

If existing cases encode the broken behaviour, changing their expectations is allowed, but each change must be listed in the PR with the sentence that says what the case is for; a reviewer will ask. Do not reference another issue's number in the test names — use this issue's number.

Scope

core/src/host/room-membership.js, core/src/host/roster.js, core/test/remote-room.test.js, a sentence in docs/subsystems/core-host.md (the naming paragraph), patches/ds-bot/ mirrors through node scripts/ds-bot-patches.mjs generate, and one changelog fragment.

Dedupe

Checked on live main 42b638c2 and in closed issues: #1949 (renaming a group never reaches seated guests), #1968 (an automatic rename never reaches guests), #1962/#1967 (settings line) and #1976/#1977 (restart names an unnamed group with the narrow formula) are all closed and each fixed a different call site. #1976 fixed the restart path only and says nothing about seat changes; nothing covers the five seat paths or the create-with-guests title. No open issue covers them.