@rustyrussell: regarding the direction of the channels, either "in" or "out", it is true that it gives us more control but I can't think of a practical use case for making that distinction. If a node's out channels are heavily penalized that means we will eventually not going to route through it's in-channels anyways.

I don't quite see a case where we'd ever set out_direction = false or direction = in. Ultimately we want to bias a node that is failing our payments when forwarding, not payments leading into a given node.

This is similar to the Boltz situation, since they keep their channels purposefully unbalanced, with most capacity on their peer's side. We temporarily fixed that by blocklisting all outgoing channels: this way we'd never end up at that node, unless it is the destination, because incoming edges are still available. And I think it can be generalized this way.

I'd vote for removing the direction param, and just always using out as the interpretation. If we ever find a reason to penalize payments into a node, then we can still re-add the direction param.