0006. Red-before / green-after is the only evidence allowed to block a sign-off

Context

Gates can audit many things: conformance rules, the whole test suite, interface tests, coverage. Most of them also see code the current fix did not touch, so gating on them blocks a correct fix for problems that already existed. A gate that blocks must answer one question for this contribution only: did the defect exist, and is it gone?

Decision

Only the per-fix C4 gate — the bundle's test fails without the fix and passes with it — blocks by default. Every other tier (runtime, conformance T1/T2/T4, interface) defaults to advisory (gating = false) and is promoted only once its targeted artifacts are clean (gate-tier policy, dce8394, 2026-06-05). A gate that cannot produce evidence (rc 77 or a PDCA-UNVERIFIABLE: line) is not a pass and not a fail: it becomes a §6 NEEDS-HUMAN item under the C6 guard (#46, 2026-06-16).

Consequences

A sign-off is blocked by proof about this change, not by legacy debt. Changes without an isolable red — new code, docs-only or test-only — land as UNVERIFIABLE C4 rows the human must judge; these are a large share of §6 today (the approach review counts 167). Instances must write a C4 gate that can actually run the red leg; a compile error that scored PASS in one instance was an Act finding.