The panel layer for "pick a scene, get a document": header, search, a
scene chip row, and a two-column card grid painted from the embedded
previews. Geometry, hit-testing, painting, and the press/scroll/hover
transitions are all in op-editor-ui, so both hosts can mount it without
either growing its own copy.
It deliberately mirrors the Prompt Center's shape — same panel size,
same chip row, same card grid — because a user who has met one should
not have to learn the other. What differs is what a card does: a prompt
lands in the chat input, a template becomes a document. So there is no
save form, and choosing a card does not open anything here. It raises
`pending_open` for the host to drain, because loading a document is a
host capability (unsaved-work prompts, recent files) that a widget
reaching into would have to reimplement per host.
Opening either centre closes the other: both are full-size centred
panels and two at once would stack card grids the user cannot see past.
Two gates learned from earlier bugs are covered by tests rather than
left to review: hover is rejected outside the card viewport, so a
pointer under the panel cannot light up a row scrolled out of sight; and
`hover_scene_template_center` returns whether the pointer is over the
panel at all, which is what a host needs to suppress hover underneath —
the exact gate the colour-variable popover was missing on 2026-07-29
when hover fell through to the layer below.
Text width comes from the Prompt Center's existing estimate rather than
a second model, so both chip rows size the same label identically.
Claude-Session: https://claude.ai/code/session_01FqKQqNj8exYwopGDpYUU7x
8a2afc7b51