Waveshaper Math

The transfer functions distortion stages actually run, as pure maths: the soft-clip saturator, both shipped bitcrush grids, the Chebyshev polynomial recurrence, an electric-piano pickup curve whose distance and alignment set how hard it bends and which harmonics it makes, a harmonic-weight solver measured off the curve itself, an exact staircase sampler for quantisers, and a linear in/out amplitude axis with forward and inverse mappings. No React, no DOM — testable in Node and safe to draw with on the server.