enqueue_exact_cost for a session-key mint that names a builder: code and
builder_fee_per_contract must be the session's approved code and at most its
approved fee (EBuilderNotApproved, EBuilderFeeAboveApproved), after the
session checks. Returns the new queue record ID.
enqueue_exact_costfor a session-key mint that names a builder:codeandbuilder_fee_per_contractmust be the session's approved code and at most its approved fee (EBuilderNotApproved,EBuilderFeeAboveApproved), after the session checks. Returns the new queue record ID.