Remark: Jet order is not shifted silently

The coefficient of ${\kappa }^2$ in $E_h$ involves the coefficient of ${\kappa }^3$ in $J_{q}G[q]$. A covariant demand at that order requires a third classical metric jet and its transformation law. It is not a condition on an unchanged two-jet alone. We use (eq:metric-expansion) for the invariant two-jet surface, and keep the exact equation (eq:E-q) when no truncation is intended.