Run the instruction drift check as a step

[sehkone]

Closes #105.

The drift check was a job calling aicers/agent-instructions/.github/workflows/check-drift.yml@main as a reusable workflow. Actions is free on a public repository, so there is no bill to cut here — what the arrangement cost was a job: a scheduling slot and a row in every one of the 15 runs of the last thirty days, for nine seconds of byte comparison. As a step it runs inside a job that already exists. aicers/agent-instructions#60 shipped the check as a composite action, and the other consumers already carry it this way.

What changed

• ci.yml: the instructions job is gone; markdown gains id: checkout on its checkout and - uses: aicers/agent-instructions/check-drift@main as its last step.
• AGENTS.md: its CI section lists the jobs a contributor should see pass. It gains a line saying that Markdown runs the drift check after the lint, and that the generated regions are not to be edited here. Outside the shared: markers.
• update-instructions.yml: the header comment said the apply moves the pin in .agents/instructions.toml. No such file exists in any consumer — the pin is .agent-instructions.toml. The other copy of that wrong path was in the job comment this change deletes.

.agent-instructions.toml and the marked blocks in AGENTS.md are untouched, the check does the same work with the same messages, and markdown keeps both its runner and its lint action — this is not a runner move and not a tool change.

Why markdown

In the consumers that have a change filter this placement is forced: the filter counts *.md as inert, AGENTS.md is a .md file, so a pull request confined to a generated region is docs-only and a step in a gated job would be skipped on exactly the change that causes drift.

This workflow has no change filter and no gated job, so that reason does not apply and the choice rests on other grounds: markdown is already the job for this class of file, it is where every sibling consumer keeps the step, and it is the job that would have to stay ungated if a path filter is ever added here. The comment already above markdown anticipates both — it says the job is kept out of check "so a clippy failure cannot hide the Markdown result, and so the lint survives if the expensive jobs are ever put behind a path filter". The same two reasons apply to the drift check.

Why the step is guarded

      - uses: aicers/agent-instructions/check-drift@main
        if: ${{ !cancelled() && steps.checkout.outcome == 'success' }}

A step's default is success(), so without this the drift check would be skipped whenever the lint ahead of it failed — hiding drift on the pull requests that touch the most Markdown. As two jobs they always reported independently, and they are independent. !cancelled() rather than always() so a cancelled run stops; the checkout clause keeps a failed checkout from being reported as drift, since the action fails outright when it cannot read the pin file and that message names the pin for a problem that is not the pin's.

Branch protection

Nothing to edit, and this is the part CI cannot demonstrate. GET /repos/aicers/multifold/branches/main/protection answers 404 "Branch not protected", so no status check is required on main and Instructions / check never was. Organization-level rulesets need admin:org to read and were not inspected — worth a maintainer's glance that no organization rule names the check this removes.

Verification

actionlint is clean on the edited file. A drift run and its revert are posted below.

[sehkone]

Test plan results

A drifted block fails. Run 34420368640 (980d6bf, one character inside shared:workflow in AGENTS.md) — Markdown failed while every other job passed.

actions/jobs/<id> reports exactly one failed step in it: Run aicers/agent-instructions/check-drift@main. Everything ahead of it passed, so the failure is the drift check and nothing else.

Also visible in the log: pinned to 0.4.0; the latest release is 0.4.0. The pin-behind warning resolved the latest release rather than reporting that it could not; the two look alike in a log and mean opposite things.

The revert goes green. Run 34421771992 (ecd9f14) — every job success. No job named Instructions / check appears in either run.

The comment already sitting above markdown predicted both halves of this: the job is kept out of check "so a clippy failure cannot hide the Markdown result, and so the lint survives if the expensive jobs are ever put behind a path filter". In the drift run Quality Check, Test, both AC-0 pipelines and Docker E2E all passed while Markdown alone went red — the first half, holding for the drift check as it does for the lint.