[vaprdev]

Summary

Bloom and tone mapping ran over the whole scene every frame, though most of it never changes. Now layout() blooms and tone-maps the static background once; each frame only the 4×4 bloom blocks whose light differs from the background are blurred and tone-mapped again. The blur and tone map loops are faster too.

 render()
   restore background
   draw what moves
-  finish(): bloom + tone map every pixel
+  finish(): bloom + tone map only blocks that differ from the background

Evidence

Scene cost per frame (step + render at 320×180, every wallpaper and time, teeming), origin/main vs this branch back to back:

	main	after
scene	2.95 ms	2.38 ms
finish()	1.10 ms	0.55 ms

Output stays within 1 level of 255 of the full-frame bloom:

Verified: typecheck, build, dev/check.ts --max-ms=60 in octant and quadrant mode (0 failed), screenshots up to date.

Merge Danger

Door: two-way

Blast Radius: Canvas.finish() for every wallpaper; a scene that changes pixels without going through the background diff would show stale bloom.