A/B palette crossfade — [palette_b] + palette_mix

Declare a second palette and bind palette_mix (0..1) to crossfade between the two per frame — smooth, audio-driven palette selection with no flicker:

[palette]
name = "ember"

[palette_b]
name = "ice"

[params]
palette_mix = "bar"        # warm on the beat, cooling across the phase

[palette_b] takes the same shape as [palette] (a name or stops). palette_mix = 0 is exactly palette A alone; 1 is palette B; between, the two LUTs are lerped. With no [palette_b], palette_mix is a no-op.

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