The WebFetch tool description now explicitly documents that https://claude.ai/code/artifact/{uuid} URLs (including preview.claude.ai) are fetchable using your claude.ai login — you do not need curl or a headless browser for these. The Artifact tool description also now includes a note: "To read an existing artifact's content: call WebFetch with its URL."
Evidence
WebFetch description update (search for "https://claude.ai/code/artifact/" and "Exception: claude.ai/code/artifact/{uuid} URLs ARE fetchable")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
