The description for the url parameter in the Artifact tool has been rewritten to cover more update scenarios:
Before: "Pass when the user gives you a URL for an artifact not published in this session."
After: "Pass whenever the user wants to update an artifact this conversation did not publish — 'update my artifact', 'keep the same link', a pasted artifact URL — and find the URL with action: 'list' if you don't have it; without this, a conversation that didn't publish the artifact always mints a new URL."
This teaches Claude to proactively use action: "list" to locate the URL rather than waiting for the user to paste it.
Artifact tool url param description (search for "find it with \action: \"list\"\ if you don't have it")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.