Gate the pull request body on AI attribution

[damian1000]

What

A reusable pr-body-scan.yml that fails when a pull request body carries an AI attribution footer, this repository's caller for it, and a third scan in attribution-scan holding new commit messages to the same bar.

Why

The existing scans read commit messages and authorship. The body was outside every gate in the estate, and it is where a footer arrives without an author writing one — the agent backend appends it at creation, whatever body was supplied, so care in the agent's own output cannot remove it.

The two tiers

History cannot be rewritten. Eight public repositories carry the commit that introduced this action, and its subject names the tool it rejects, so a pattern strict enough to bar a bare mention would fail all eight permanently. The strict pattern is therefore aimed where it can be met:

Surface	Bar
History, read with --all	attribution artifacts: a footer, a trailer, a tool identity
Commits a pull request adds	any mention, CLAUDE.md excepted
The pull request body	any mention, because a body is rewritable

Load-bearing decisions

• Live read, not the event payload. github.event.pull_request.body is frozen at the instant the event fired, so a footer stripped a second after creation would fail a payload read permanently, on a pull request that is already correct.
• Callers trigger on edited. Correcting a body raises no other event; without that type a corrected body could never clear the check. synchronize is separate — a check run attaches to a commit, so a push must re-report.
• The range scan is guarded to pull_request. There is no range on a push event, and history is the other tier's job.

Testing

• actionlint 1.7.12, the version and checksum lint.yml pins — clean.
• Prettier 3.4.2 over the workflow and markdown targets — clean.
• Strict pattern exercised against a bare mention, a vendor name, an oblique description and CLAUDE.md — correct on all four.
• Every repository's full history measured against the strict pattern: eight fail. That measurement is the evidence for tiering rather than tightening the --all scan.
• Run block simulated against a body carrying a footer, a body describing one, and a null body.
• This branch's own commits measured against the range scan — clean.

The caller here resolves the scan by local path, so this pull request is gated by the files it adds, and this body is written to pass the rule it introduces.

Not done here

Adoption. Buildable repositories reach shared workflows at @main, so nothing picks up the body scan until this merges, and each then needs its own thin caller — ci.yml cannot host it. The range scan, living inside the action, arrives everywhere the moment this merges. Required-check contexts in estate-infra are a separate decision, with the blast radius document 02 records for 2026-08-13.