Second measurement round: the driver render pin is STEREO-ONLY — the
mono render stamp turned the endpoint unopenable (0x88890008 on every
open, the incoherent-stamp signature the pad program documented). Since
the crossing is raw, the coherent choice inverts: the CAPTURE side now
declares the stereo float stream that actually crosses (fixing the
octave-low voice), and the render has its stereo float default stamped
explicitly — pinning the pair AND healing any endpoint a previous build
left mono-stamped.