signal_field_from_multistatic renders a 20×20 floor-plan heatmap by
overlaying isotropic Gaussians at each ESP32 node's configured 3D
position, scaled by cv²(fused_amplitude) × cross_node_coherence.
Replaces ADR-105 D6's zero grid only when ≥2 nodes are active AND
positions are configured (--node-positions); else preserves the zero
grid (ADR-105 honesty contract).
Honestly framed as a coverage × activity map, not a target-position
estimate — commodity ESP32s have no phase-coherent ranging.
Verified end-to-end: 320/400 cells non-zero with two live sensors
at (1.5,2,1) and (-1.5,2,-1), all-zero on single sensor / no-position
deployments. cargo test --workspace passes (313 tests).
Co-Authored-By: claude-flow <ruv@ruv.net>
c8ac60f6ab