Currently we provide a WeightProvider interface that allows modules to declare their runtime weights so that the appropriate transaction fees can be charged. This unfortunately only works for requests and responses. We should eventually switch to a simpler callback mechanism which should return the PostDispatchInfo for the handle extrinsic.

#[cfg(not(feature = "unsigned"))]
#[pallet::weight(get_weight::<T>(&messages))]
#[pallet::call_index(1)]
#[frame_support::transactional]
pub fn handle(origin: OriginFor<T>, messages: Vec<Message>) -> DispatchResultWithPostInfo {
        let signer = ensure_signed(origin)?;

        Self::execute(messages.clone())?;

        // do anything, but return the `PostDispatchInfo`
        T::FeeHandler::on_executed(messages, signer)
}

This allows for a wider variety of fee collection strategies as well as free transactions, or even negatively priced transactions for consensus update incentives.