Remove property contentSection, the dead Page document nodes and the PageSection config
28 transforms pass property: 'contentSection' to createComponentRenderable, which emits data-field="content-section" on the rune root. Nothing reads it. The one consumer that ever existed, the Page document node, compares the camelCase 'contentSection' against the kebab-cased attribute, so it could never match, and it is never registered by any Markdoc config. Page also stamps typeof="PageSection", which is not a schema.org type. SPEC-133 decided the removal; v0.35.0 deferred it because it changes HTML on every section rune, and nothing has carried it out since.
It lands first in v0.43.0 because it touches the runes SPEC-160 changes next, and it removes one recorded plugin-vs-composed difference from the four composed-storytelling tests before WORK-653 re-runs those comparisons.