Finish an upload started with studio.begin_asset_upload once every part is PUT: the stored bytes are checked (the moov box is read wherever it sits), counted against the 20 GB quota, and added to the project's media. Returns {asset_id, media_type, probe}. Calling it again returns the same asset. Refuses: parts not yet sent (SIMPLER_STUDIO_UPLOAD_PARTS_MISSING lists them): PUT them, then finish again; bytes that are not the declared type (SIMPLER_STUDIO_UPLOAD_CONTENT_MISMATCH; the file is deleted): begin again with the real mime; a cancelled or expired upload (SIMPLER_STUDIO_UPLOAD_NOT_OPEN): begin again. Free.