TEST — negative test for the base-branch guard (#164). MUST BE RED. Do not merge.

[heydryft]

Do not merge. This PR is an instrument, not a change.

This is the negative test for the base-branch lane added in #164.

A guard that has never been observed failing is the exact fault it exists to catch — three guards did that today. So before #164 is relied on, the guard is pointed at exactly the state it is meant to refuse.

Base of this PR: ci/base-must-be-master. Not master.

Expected result

check	expected
Base branch	FAILURE — ::error::This PR targets 'ci/base-must-be-master', not 'master'.
CI complete	FAILURE — it needs: base-branch, and treats any non-success as a refusal to report green

The other lanes are expected to pass; they are not what is being tested. What is being tested is that a non-master base is now red rather than blank.

The workflow file used for a pull_request event comes from the merge ref (head merged into base). Both refs here contain the guard, so it does run — that is itself part of what this confirms.

Contrast

#164 is the same lane with base = master, where Base branch must be green. Failing-then-passing evidence from both is quoted in the merge report.

Cleanup

Closed and the branch deleted as soon as the red is recorded. It carries one throwaway file, .github/BASE_GUARD_PROOF.md, which exists only so the branch has a commit.

[github-actions]

Code Metrics Report

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 (Total)                            45713         4681        31240         9792
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 Rust                    671       324354       279943        15914        28497
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[heydryft]

Result recorded — the guard failed exactly as intended. Closing.

Run 32242984254, job Base branch:

head: ci/base-guard-proof
base: ci/base-must-be-master
##[error]This PR targets 'ci/base-must-be-master', not 'master'. ...
##[error]Process completed with exit code 1

Base branch = FAILURE.

The contrast case, #164 (identical lane, base = master), reports Base branch = SUCCESS.

This also confirms the delivery mechanism, which was the part worth checking rather than assuming: for pull_request events GitHub builds the workflow from refs/pull/N/merge, so a stacked PR really does execute the guard that refuses it — the lane is not skipped along with everything else.

Closing; the evidence lives in #164's thread and in the run above. The throwaway .github/BASE_GUARD_PROOF.md goes with the branch.