Upload an image and get back a stable URL the editor can drop into <img src>.

Upload a single inline image and return a URL you can reference in the document via <img src="...">.

Accepts PNG/JPEG/WebP/GIF/SVG, up to 10 MB per upload. The returned url is a time-limited signed link (image storage is private; images are always served via signed URLs) that renders immediately in the editor; on save the backend normalizes it to the stable canonical reference, and every subsequent read re-signs it fresh. canonical_url is that stable stored form. Useful for saving a drawing or screenshot so a document can embed it.