~x-ai/grok-latest → A (3:1)

A fixes a real multi-user failure: shared WEB_BROWSER_AGENT sentinels bound on first browser vote and blocked later humans, replaced by Option<agent>/None delegates with a focused regression test for two users voting. B mainly renames room HTTP paths (/r/short/slug → /r/{short}{slug}), centralizes that encoding, and adds URL identity helpers—useful structure, but largely route churn and niceties versus A’s correctness fix.