WritingView passed chapter.doc.content (a bare ProseMirror node array)
as the editor content, which made EditorState.create build a doc node
with an undefined type, throwing 'Cannot read properties of undefined
(reading schema)' and unmounting the write view. Pass the full doc
object ({ type: 'doc', content }) on init and on setContent sync.
Add editor regression tests covering schema instantiation, node
registration, and doc-content round-trip.
Schwitzz
015e18ff96