Create a canvas project from a Fabric.js toJSON serialization (canvas_json, required): every embedded data:image src is pulled out, hashed, and written to a tenant-scoped, content-addressed R2 key before the row is saved, so canvas_json never carries image bytes and identical images dedupe across projects. SVG, an unrecognized image type, an oversized embedded image, or a canvas still too large after externalization refuse the whole create — nothing is silently dropped. An optional thumbnail_data_url is externalized the same way into thumbnail_key; thumbnail_key and version are server-set and refuse if you pass them. NEXT: edit_project_update to autosave the same project as it changes.