Add a purely-visual, transient juice layer over a committed move — score
popups + a tinted particle/flash burst at the clears — with no change to the
model, score, moves, or settled board.
- assets/fx/particle.png: key the painted transparency checkerboard out of the
provided particle art to real alpha (8-connected border flood fill +
smooth luminance falloff that preserves the soft glow), downscaled to a
256x256 RGBA white sparkle. tools/key_particle.sx is the reproducible tool.
- board_fx.sx: BoardFx (live particle bursts + one "+points" popup) and
BoardFxAssets. The engine image path samples texture*white (no draw-time
tint), so the white sprite is tinted per gem colour at LOAD time into one
texture per colour; a burst animates by scale (grow -> shrink) and the soft
texture edges carry the fade. Combos (cascade depth > 1) burst bigger and the
popup is larger + gold. All driven by delta_time and self-pruning.
- board_anim.sx: AnimMove carries the model's cascade.awarded so the popup
shows the real payout without re-deriving any scoring in the view.
- board_view.sx / main.sx: wire BoardFx + the tinted assets, tick each frame,
spawn on a legal commit, and render bursts (clipped to the grid) under the
popups (drawn on top). Input-lock (BoardAnim.active) is untouched; FX never
gate input and may outlast the move slightly before vanishing.
Goldens (iPhone-17-class sim, iOS 26): p6_fx.png (combo: gold "+480" + bursts
mid-cascade), p6_fx_match.png (single match: "+30" + red burst), p6_fx_after.png
(settled board, FX fully gone). Gate: ios-sim build links, 15/15 logic tests
green (scoring/cascade goldens unchanged).
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