The canonical Craft.js state from real saves shows that layout shells
(Section, BackgroundSection, HeroSimple, FeaturesGrid, ColumnLayout,
CTASection, FormContainer, Navbar, Footer) all serialize with
isCanvas:false. Only Container instances are canvases. The shells use
internal <Element canvas id="..."> linkedNodes for their drop targets.
Our previous CANVAS_TYPES set claimed all those shells were canvases,
which made Craft.js's toNodeTree walker hit an uncaught Invariant —
the shell asserted "I'm a canvas" but its render ignores data.nodes,
so the walker would chase phantom children.
Josh Knapp
849f432330