Follow Button Part 1

Basics: stage 470×222px, background #13131C, all coordinates in px from the stage's top-left, everything clipped to the stage (its two top corners are rounded with radius 40px; the bottom corners are square). The animation is a 2s loop that plays by itself and is seamless; the video is 12s = six loops. T = seconds since the video start; u = (T + 0.25) mod 2 (the first frame is already 0.25s into a change). One tap every second, always at the button's center: at u = 0 the state becomes Following (st = 1, count 1,285), at u = 1 it becomes Follow (st = 0, count 1,284). lastTap(u): k = floor(u) (0 or 1), dt = u − k, to = 1 if k = 0 else 0, from = 1 − to. Every value depends only on u, so 2.0s equals 0s; every reaction has settled before the next tap. Colors: violet #6E5BFF, cyan #38C6FF, pink #FF5CA8, mint #3DDBB0, dark fill #1C1B2B, edge #3A3852, gray text #7F7D9C, light text #F4F4F8. "violet→cyan" is a horizontal linear gradient from the given left x (violet) to the given right x (cyan). mix(A, B, k) = per-channel linear RGB blend. Text: font stack "Segoe UI Variable Display","Segoe UI",sans-serif, weight and size as given; all text in this piece uses textBaseline "middle"; x is the left edge unless "centered" or "right-aligned". rr(x, y, w, h, r) = rounded rect from its top-left. Easing (k clamped to 0–1): ease = 1 − (1−k)³; easeIn = k³; easeIO = 4k³ for k < 0.5, else 1 − (−2k+2)³/2; easeBack = 1 + 2.9(k−1)³ + 1.9(k−1)² (overshoots about 10%). lerp(a, b, k) = a + (b−a)k; clamp(x) to 0–1; seg(x, a, b) = clamp((x−a)/(b−a)); bump(x, a, b) = sin(π·seg(x, a, b)). Spring springF(ω₀, ζ)(t) = 0 for t ≤ 0, else 1 − e^(−ζω₀t)(cos ω_d t + (ζω₀/ω_d) sin ω_d t), ω_d = ω₀√(1−ζ²). Check mark check(cx, cy, s, prog, lw, color): a round-capped, round-joined polyline through (cx − 0.30s, cy + 0.02s), (cx − 0.09s, cy + 0.23s), (cx + 0.32s, cy − 0.20s), drawn up to the fraction prog of its length.

The button flips over its horizontal axis like a coin; the other side is the new state. 
- sc = press with depth 0.06. f = springF(7, 0.6)(dt) (about 6% overshoot, settled by ~0.8s); θ = π·f; c = cos θ; s = |sin θ|.
- Visible side: st = from while c ≥ 0, else to. Vertical scale ky = max(0.002, |c|).
- Draw: scale around (235, 161) by (sc·(1 + 0.04s), sc·ky); face(st, 1) with glow = 1 − s; if s > 0.01, the button rr filled black at opacity 0.45s on top (the turning side darkens). Profile and count as in Basics.