docs(agents): record what let an unverified conjunction reach users - #432

#431 retracted the claim. This records the cause, because the instance is the
least interesting part of it.

Both inputs to the false statement were real and each had been checked
independently: release_anchor_audit.rs genuinely is absent from the v2.3.9 tag,
and v2.3.9 genuinely is where the anchor drift was found. What was never
checked was the conjunction -- that v2.3.9's release body therefore DESCRIBED
the audit -- and checking it was one command:

  gh release view v2.3.9 --json body

That body says the eight drifted documents "All now read v2.3.9", a manual
re-synchronisation which is in its tag, and contains no occurrence of
"release_anchor_audit", "standing", "gate", or "15 anchors". Verifying every
premise is not verifying the conclusion drawn from them.

Two propagation mechanisms matter more than the instance, and the bullet names
both.

The sentence was written into AGENTS.md during the v2.4.0 work, and the v2.4.1
release summary was then drafted FROM AGENTS.md. That is the laundering step:
an unverified claim entering this file is indistinguishable from a verified one
by the time the next release quotes it, and it then reaches a published release
body, a commit body, a PR body and a report to the maintainer in a single pass.
AGENTS.md is a notes file, not an oracle, and this is the first entry that says
so about itself.

The claim also had the shape this project rewards -- a recursive irony, "the
same failure one level up". That shape actively suppresses the check, because
it reads as an insight rather than as an assertion needing evidence. The
house style's appetite for findings of that form is exactly why it needs a
verification bar rather than less of one.

The bar stated: before writing that a document, release, commit or person SAYS
something, open it and grep for the words.

Nothing else changes -- one bullet, inserted beside the sibling traps it
belongs with (the reviewer-claim bullet it now precedes is the same failure
with a different source).