The firearm Houston keeps concealed under his robes, punching a hole through Carl's shoulder at the ceasefire's end.
When Phase One Combat engages, Architect Houston jumps up and his robes fling back to reveal a bug-like body with six arms — two of which are holding a rifle, which he brings to bear on Carl's chest and fires.
Carl dives and takes the round through his shoulder instead of the heart, landing against a counter and dropping an impact Hob-Lobber as Baroness Victory's teleport pulls him clear. He slams a Healing Potion on arrival at the Field Hospital, crying out as the wound knits. The weapon choice is deliberate: with offensive magic banned in the ramp-up phase, a rifle is the fastest legal way to kill a warlord.
A rifle large enough to require two of Houston's six arms, concealed beneath his robes throughout the inquiry.
The weapon of Houston's assassination attempt on Carl.