- // If an amount transferred by the path is updated, the fees should be adjusted. Any other way
- // to change fees may result in an inconsistency. Also, it's only safe to reduce the value,
- // to not violate channel upper bounds.
+ // If the amount transferred by the path is updated, the fees should be adjusted. Any other way
+ // to change fees may result in an inconsistency.
+ //
+ // Sometimes we call this function right after constructing a path which has inconsistent
+ // (in terms of reaching htlc_minimum_msat), so that this function puts the fees in order.
+ // In that case we call it on the "same" amount we initially allocated for this path, and which
+ // could have been reduced on the way. In that case, there is also a risk of exceeding
+ // available_liquidity inside this function, because the function is unaware of this bound.
+ // In our specific recomputation cases where we never increase the value the risk is pretty low.
+ // This function, however, does not support arbitrarily increasing the value being transferred,
+ // and the exception will be triggered.