An empty section renders as nothing. That is correct on the public site and useless in an editor:
somebody who has just chosen "two columns" sees a blank page and has to take it on trust.
So the canvas outlines every band it finds, names it, says its shape, and offers Delete — and outlines
the columns inside it, because a one-column band and a two-column band are identical until something is
in them, which is exactly when it is too late to notice the wrong choice.
The site provides three attributes and no behaviour: data-page-empty, data-section-id, data-column.
Markers rather than classes, so they cannot be mistaken for styling, cannot be purged by a build that
has never heard of this file, and read as what they are. That is the whole contract — one attribute on
the public site buys the entire editor.
Section names and layouts are FETCHED, not read out of the DOM. The markup says which row a band came
from and nothing else; inferring the layout from its classes would be the admin reading the site's
stylesheet, which is the coupling all of this exists to avoid.
── The race, and why the fix is not another ref ──
Creating a section starts two things that do not finish in a fixed order: the frame fetches a new
document, and the panel fetches the sections to draw on it. Painting only on load meant painting with
whatever had arrived by then, which after a create was usually the data from before it existed.
So SitePreview re-runs the injection when EITHER moves — `loaded` is state, `onDocument` is a
dependency, and whichever arrives second triggers the paint that counts. The caller then controls
repainting through its own useCallback dependencies, which is what those are for.
The handlers still go through a ref, and the data does not. Callbacks are rebuilt every render and
would repaint on every one; the sections are the thing being drawn and should be exactly what decides
when to redraw.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
pastilhasandClaude Opus 5
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