ab81bb6e

By: ValentinHirschi <valentin.hirschi@gmail.com>

checkpoint four-loop numerical inventory and pinch regressions

Six fast checks pass. The opt-in 16-pair matrix passes four H pairs and FG D1, then exposes an FMFT-only FG D7 cancellation mismatch. Retain this failing regression without weakening tolerance; public four-loop RustRed integration remains pending.