First comparison

List animation needs to distinguish two ideas:

1. A logical ID says which domain item this is.
2. A transition key says whether this is the same continuous visual presence.

An item that only moves keeps its transition key. When an animation layer retains its exiting DOM, an item that returns before that exit finishes needs a second key for its new visual presence.

The invariant

same ID + continuously present  -> retain key
same ID + absent then present   -> allocate fresh key
duplicate ID in one frame       -> reject the whole frame

The untreated pane uses item.id as the framework key. The readable default updates state every 1,000 ms while each FLIP and exit runs for 3,000 ms; both values are adjustable above the lists. The loop advances from A/B/C to D/A/B, C/D/A, and B/C/D before returning to A/B/C, so correct movement always goes downward. When C returns on frame 3, FLIP reuses the still-exiting keyed DOM and pulls it upward into C’s new slot. Likftc keeps old C on one nanoid transition key as an out-of-flow overlay while new C enters on a different nanoid transition key. Every pane keeps three layout rows even while multiple exits remain in the DOM.