nx_contactfriction_gate.nx

nx_contactfriction_gate.nx -- FRICTION IS REAL AND ITS ABSENCE IS HONEST (softbody SB3, first leg). WHAT THIS PROVES. Press a probe into the tissue, then DRAG it sideways, and measure how far the tissue follows. With a high coefficient the surface is carried along; with mu 0 it slides and the surface stays. That difference IS friction -- a normal-only contact cannot produce it, and neither can a blur. THE THIRD STATE IS THE POINT. mu has three answers, not two: a number, ZERO, and UNSET. Zero is a measured frictionless surface. UNSET means no citation exists and the solver declines to invent one -- and the estate has NO cited macroscopic skin-on-skin Coulomb mu whose bytes it has read (the two papers fetched 2026-08-25 give a Frictiometer device index and microasperity values of 0.004/0.001; the quoted 0.2-0.5 band is from a review nobody here has read). So UNSET is today's honest production state, and this gate proves it BEHAVES like frictionless rather than silently defaulting to some plausible number. The mu used below is a FIXTURE VALUE for proving the mechanism, never a claim about skin. license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0