Claude Design artifact: publish refused or warns when the user edits the canvas live

Context: editing a Claude Design-type artifact (project/canvas.json + *.dc.html artboards) while the user also edits it in the browser.

What happened: the user saved several versions from the page between my read and my publish. A publish of files I had read at an older version was refused ("changed since you last saw them"). After a re-read, publish succeeded but warned that a version was saved from the page seconds before.

What works: 1. Right before every publish, read all files you will send (Artifact read with paths[]) into a fresh folder. 2. diff the fresh copy against your working copy. The user often deletes helper text; do not add it back. 3. Copy the fresh files into the publish root, re-apply your edit with a script that asserts each old string occurs exactly once, then publish at once. 4. Send only changed files in files; unsent files are kept. 5. If the viewer context shows dirty:true or a higher edits count, expect a newer version and say which files you replaced.