The flat room list was a bare map(), so Lit reused room nodes by position.
On a floor switch the previous floor's room node became the new floor's room
and `.room { transition: 0.12s }` drew its fill and stroke in from the old
computed values: one paper-white frame, then two or three frames darker than
the final fill (alpha rises while fill-opacity falls), then the fill. Between
two filled floors the fill bled in from the other floor's colour.
The list is now keyed(space.id, repeat(rooms, (r, i) => r.id || i, ...)), the
shape #534 settled on for openings and markers. The outer key handles the
floor switch, including room ids repeated on two floors (ids are unique only
within a space); the inner key keeps a node bound to its room inside a space,
where inserts, merges, splits and the editor filter shift positions. An
id-less room keys by its numeric index, which never equals a string id. The
transition itself stays: it smooths hover and a real fill change on the same
floor.
Witness: a new section of smoke_space_switch_transitions, before physicalize
(after it the first room changes template branch and the node is recreated
anyway). Red on dev: five transitions on g1, node r1 reused for g1, computed
fill rgba(0, 0, 0, 0) / 1; room nodes swapped by an insert; same-id case
reuses r1. A real custom_fill change still runs a fill transition (catches
`transition: none`). Two mutants: inner key removed, outer key removed.
Issue: #742
User-Visible: yes
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018qZfe7YS4rqEMKoVeS3GKd
