The probe steps a Zone, lowers its flow through VolumeSampling.LowerFlow, dispatches the HLSL
globalFlow and slopeFlow, and compares with FlowField (max error 1.0e-4 of amplitude, tolerance
1e-3). All commits build; the Unity side was verified from this tree.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>