process: require verify-reduction before implementing reduction rules

[zazabap]

Summary

5 unsound reductions were merged in PRs #779 and #972 (see #1006). All would have been caught by the /verify-reduction skill (PR #979), which produces Python constructor + adversary scripts with YES/NO instance testing. But the skill wasn't required — the rules went straight from issue description to implementation.

Meanwhile, PR #992 applied /verify-reduction to 34 proposed reductions and caught 8 refuted ones before they were ever implemented. The methodology works; it just wasn't mandatory.

Root Cause

The add-rule and issue-to-pr skills don't require verification before implementation. The implementation pipeline is:

[Rule] issue → issue-to-pr → add-rule → implement → review-structural → merge

The verification pipeline exists separately:

[Rule] issue → verify-reduction → constructor + adversary (YES+NO) → verified artifacts

These two pipelines are disconnected. A rule can be implemented and merged without ever running the verification.

Proposal

Wire /verify-reduction into the implementation pipeline as a mandatory gate:

1. add-rule skill — require NO-instance test

Add to the testing requirements: a test that constructs an infeasible source instance, reduces it, and brute-force verifies the target is also infeasible. This is the minimum bar — 5-10 lines of test code that would have caught all 5 unsound reductions.

#[test]
fn test_source_to_target_no_instance() {
    let source = Source::new(/* infeasible instance */);
    let reduction = source.reduce_to();
    let result = BruteForce::new().find_witness(&reduction.target_problem());
    assert!(result.is_none(), "NO instance should have no feasible target solution");
}

2. issue-to-pr skill — run verify-reduction first

When processing a [Rule] issue, check if /verify-reduction artifacts exist. If not, run it before generating the implementation plan. This ensures the mathematical correctness is established before any Rust code is written.

3. review-structural skill — check for NO-instance test

Add to the structural checklist: "Does a test_*_no_instance (or equivalent adversarial test) exist in the test file?"

Evidence

Approach	Reductions checked	Unsound found	False negative rate
Current pipeline (no verification)	43 (PRs #777-#972)	5 found post-merge	12%
verify-reduction pipeline	34 (PR #992)	8 caught pre-implementation	0% (none merged)

Related

• bug: 5 unsound reductions — reduce_to() constructions are mathematically incorrect #1006 — the 5 unsound reductions this would have prevented
• PR feat: add verify-reduction skill #979 — the verify-reduction skill (not yet merged)
• PR docs: batch verify-reduction — 34 implementable reductions verified #992 — batch verification that demonstrated the methodology works