Rendered the old and new heuristic over the 24 procedural demo scenes: the
rewrite sharpens edges on blue skies (beach, dunes, canyon), but drops warm
sunset and dark night skies to nothing, punches a hole around the sun, and
selects lavender rows, a flower and lit mountains as sky. It also changes the
render of every existing Sky mask without a process version. Back to main's
heuristic; the masking-view part of this PR stays.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>