The clone threshold ratchet is not enforced mechanically #409

docs/engineering/quality-gates.md (Clone gate) says the tests ceiling only falls. Since #439 (2026-10-17, maintainer delegated to the lead) the rule keeps a minimum headroom: the ceiling is the measurement plus 0.25 points, rounded up to the next 0.5%. The old rule, plain rounding up, could leave almost no headroom: 5.48% would have given 5.5%, with 0.02 points.

Nothing enforces that. The ceiling stayed at 8.5% (tools/OpenCode.Sdk.Tools/Clones/CloneScopes.cs) while the measurement fell to 7.64%, then 7.2% across the TST-E7 moves, and no pull request applied the ratchet. TST-E0c lowers it by hand to 7% (6.81% measured at its head, rounded up to the next 0.5%), but the next change that removes clones can again forget.

Suggested fix: a test that fails when the tests scope's ceiling exceeds the current measurement plus 0.25 points, rounded up to the next 0.5%. It would read the measurement from verify-clones or the tests scope's report, and the failure names both values and the ceiling to set. The tools/ ceiling (3%) is a fixed cap, not a ratchet, and stays out of it.

Out of scope for TST-E0c.