tolerancePercent

share of pixels this fixture alone may differ by, overriding the run's own setting (viddik.tolerancePercent, otherwise 0.05%). Unset by default, and meant for the fixture that provably can't hold the strict number — a known-unportable rendering path, not a fixture that has started failing. The engine's 16-pixel floor still applies underneath, so this loosens a fixture rather than tightening it below a handful of pixels. @Preview has no counterpart, so this one is only ever read here.