Verified at this commit:
  - emitter symmetry: diagonal/axis ring ratio ~1.00 on circ and rectroom
    (was 1.18-1.21), and left/right ~0.98 on the pinhole lamps (was 1.6-1.9)
  - bounce pass measurably active in orbit and text; zero effect elsewhere by
    design, since no other scene authors albedo
  - all 8 scenes render headless, and the repo smoke test passes on the
    interactive path