Stokes drag: F(η=r=v=1) = 6π; F(2v)/F(v) = 2; F(2r)/F(r) = 2 (triple linearity fingerprint)

Drag evaluations: F at (η,r,v) = (1,1,1) = 6π exactly (unit-argument reference); F(2v)/F(v) = 2 exactly (linearity in v); F(2r)/F(r) = 2 exactly (linearity in r). Canonical pins: F symbolic form; F at unit arguments (6π); ratio at 2v (2);…