DOMTokenList.supports() threw "DOMTokenList has no supported tokens"
for relList and sandbox because they were created without a supported
set. Vite's modulepreload polyfill runs link.relList.supports('modulepreload')
at the top of every bundle, so the throw aborted the whole ES module and
React/Vite SPAs rendered blank. relList and sandbox now carry their token
sets; classList still has none and correctly throws.