A full fiber-tensor check for B 6

The following calculation sharpens the inherited monomial diagnostic. It does not replace the complete six-branch test.

For a covector $p$, put $n=p^{♯}$ and suppose $p^2=0$. Let $G_{\mu \nu }$ be the residual metric value at its source vertex, let $k_{\mu }$ be the residual scalar derivative at the interaction, and set