zio (-Dbackend=zio) has been prod since 2026-08-05 canary #2; the top-level docs still described the Io.Threaded era. update CLAUDE/AGENTS, README, design.md (long-term async section closed with the outcome), deployment.md (backend build flag + rollback path). drop the June merge-TODO and crashloop handoff — both self-marked for deletion once the fix landed, which it did (websocket fixes upstreamed, direct dep back at v0.1.11). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>