f clarify comment

Author: TheBlueMatt

lightning/src/routing/router.rs

@@ -733,6 +733,20 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 									// cheaper fee, check that it was because the second path we
 									// found (which we are processing now) has a lower value
 									// contribution due to an HTLC minimum limit.
+									//
+									// e.g. take a graph with two paths from node 1 to node 2, one
+									// through channel A, and one through channel B. Channel A and
+									// B are both in the to-process heap, with their scores set by
+									// a higher htlc_minimum than fee.
+									// Channel A is processed first, and the channels onwards from
+									// node 1 are added to the to-process heap. Thereafter, we pop
+									// Channel B off of the heap, note that it has a much more
+									// restrictive htlc_maximum_msat, and recalculate the fees for
+									// all of node 1's channels using the new, reduced, amount.
+									//
+									// This would be bogus - we'd be selecting a higher-fee path
+									// with a lower htlc_maximum_msat instead of the one we'd
+									// already decided to use.
 									debug_assert!(path_htlc_minimum_msat < old_entry.path_htlc_minimum_msat);
 									debug_assert!(value_contribution_msat < old_entry.value_contribution_msat);
 								}