Blending-focused plan for Phase 3c: port WorldBuilder's per-cell
palette-code + alpha-atlas terrain texture merge scheme so terrain
type boundaries blend smoothly instead of stair-stepping.
Scope deliberately excludes chunking (deferred to a possible Phase 3d
when streaming actually matters) so the work stays focused on the
visible win.
Execution split into 4 small commits:
3c.1 palette math (pure CPU, unit tested against golden values)
3c.2 alpha atlas loading
3c.3 per-cell vertex layout refactor
3c.4 shader rewrite (the visual-win commit)
Each step is runnable on its own so if 3c.4 looks wrong we know the
earlier steps were fine.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
