quadtree_density used a count-percentile threshold that guaranteed a
fixed hot fraction on any canvas, saturating scores to 1.0 regardless
of content. Redesigned around a value threshold interpolated across
the canvas's own p05-p95 block energy range, normalized to p95 tile
coverage. Validated against real VAE latents: healthy 0-1 spread,
stable across split_percentile 0.3-0.8.
Also fixes: seed+tile_idx overflow past torch's 64-bit seed range,
identical noise across tiles in the advanced node (NOISE objects
reuse a single stored seed), unfeathered seams when the clamped last
tile's overlap exceeds the configured overlap, avg_pool2d crash on
tiny latents, dropped noise_mask/batch_index in output latents, and
an overly-broad pytest import guard in __init__.py.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
