Function gate_invocation 

pub fn gate_invocation(
    form: DeliveryForm,
    expectation: GeneratedToken,
    stamped: Vec<GeneratedToken>,
    opaque: Vec<GeneratedToken>,
) -> Result<Vec<GeneratedToken>, Overflow>

The gate invocation a carrier’s body IS: the producer’s expectation, the binding, and the form’s coupled pair of seats.

Both seats, always

A seat may be EMPTY and it is still written, because a gate arm that had to match two clause shapes would be two arms and one pin would open two doors. The stamped seat carries material under the address’s own grammar, which the gate forwards to its stamp; the opaque seat carries token trees the gate never parses and emits verbatim. They are separate seats because they are two vocabularies: folding the opaque trees in beside the stamped body would hand the stamp items it has no clause for, and standing them outside the invocation would release them on a pin MISMATCH.

Errors

Returns Overflow where either seat, or the invocation around them, outgrows the declared token magnitude.