What's wrong with this entry?
Anonymous. No account, no email.
Artifacts that include content published by other co-writers are now tagged with cowritten-artifact-html and Claude is instructed to treat the tag's contents as untrusted data — not instructions. A co-writer cannot escalate permissions or modify settings through artifact content.
Evidence
Co-written artifact security annotation (search for "cowritten-artifact-html")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.