Oh, that is a neat side-effect... reinforcements means faster logout time. Kills 2 birds with one stone.
I like this, actually, but maybe it would be good to limit its power somehow... for example, if you had an ability that costs gems or something which can temporarily disable another Hunter's reinforcements ability, that would be interesting.
It would be easy to charge a fee in HUC depending on what is in the message field.
The fees for new hunters and for destruct are calculated here
https://github.com/chronokings/huntercoin/blob/master/src/gamestate.cpp#L527
and "destruct" and "message" are both part of "Move".
Example for a counter spell that prevents the enemy horde from attacking but not logout:
If an hunter is found who said the right word ("negatur egressus"?) not too long ago (60 blocks?) in the message and is near that bank
(perhaps adjacent tile only) all summoned are due for despawn+refund before they can move, attack or take damage again.
Trivial to implement, everyone additionally get an "ch.stay_in_spawn_area = 2"
The spell effect would move around (and die) with the hunter who casted it. The attacker must kill the "gate keeper" before getting in.
Or cast it onto yourself to make logout even faster and safer. (it would be too late for an enemy near the bank to kill'em all)