# PH-SYM-001

**Name:** C4 rotation equivariance violation

**Severity:** warning

**Input modes:** adapter+dump

Discrete rotation equivariance (C₄ action on a 2D periodic square grid).
The rule applies a discrete 90° rotation to the input field, queries
the model on the rotated input, applies the inverse rotation to the
output, and compares against the original output. The raw value is the
relative discrepancy on a calibrated noise-floor band; the rule fires
when the model breaks discrete rotation symmetry on a square-domain
problem with rotational structure.