debugTintFailedSteps top-level property
The tint steps (1 or 2) a room's tint builder treats as failing to
triangulate (Ruling 10-16). Honest rooms reach D9's steps 2 and 3 (RG2
has both); the seam exists to exercise the room's local-frame
triangulation guard (_storedTint), which no honest fixture reaches:
RG2 and DG3 set it. Null in the library, which never sets it; tests
restore it to null in tearDown.
Implementation
@visibleForTesting
Set<int>? debugTintFailedSteps;