Each marker now says available-at-tag in the guide's existing L420
phrasing, verified by tag containment in #221; every never-mix-refs
sentence survives verbatim. The convention paragraph gains its missing
half: the release PR that ships machinery clears, in that same PR,
every marker its assembled section makes false.
Refs #221
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
