The routing node forwards this to the next hop with lower htlc amount, lower forward up-front payment, higher backward up-front payment, and shorter grace period. However, there is an issue related to trustless offchain-to-onchain swaps, where the swap service will generally be forced to pay up the hold fees as claiming the offchain side is dependent on claiming of the onchain side of the trustless swap mechanism which is slow. The hold-fees mechanism cannot be ported over in the onchain side, so the swap service would need to issue a separate invoice to pay for the hold fee for the "real" swap payment. To mitigate against this, a combined mining-fee+hold-fee invoice would have to be issued at the same time as the "real" swap invoice.