CLAUDE: test 6 - sky-band root cause reproduced: symmetric-extension crease response to LINEAR content

Constant -> exactly 0; ramp 5/row -> 8-row-periodic band pattern
(0,-0.008,-0.297,-0.547,+0.547,+0.297,+0.008,0) = the LOG-01 run's measured sky
bands scaled by the gradient (2.5/row -> -0.14,-0.30,+0.35,+0.16). Pure double
CPU chain -> not float32, not GPU, not a kernel coefficient: pixel LoG of a ramp
is 0 (odd symmetry) but the per-tile symmetric convolution sees the mirrored
extension's slope crease at tile boundaries. Inherent to any per-bin TD multiply
(present under aberration kernels too, masked by content - Andrey's LPF-era
artifact class, confirmed in substance).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>