Proven in practice: the god erupts from the vessel like a chick from an egg, and taking the vessel away takes the god away.
The mechanics Carl was told become facts he can see. The system's own warning reads: this god has been involuntarily summoned to this location, summoning rules apply. The mangled ManTauR cracks in half with a burst of steam while the world is still frozen, because the god must emerge from his vessel like a chick from an egg, and light bursts from the body the instant the freeze lifts. Grull then grows until his head is halfway to the ceiling — four storeys at the front, and still visibly a miniature of his true form — and a pulsing red star spins on Carl's map like a buzzsaw.
The rest of the rules hold too. There is no cooldown: five punches into the second, amputated vessel restarts the summoning ten seconds out, and Grull immediately breaks off his hunt and turns toward the new call. And the summoning follows the vessel: when the second mantaur goes through the portal to The Abyss with one second left, Grull — mid-charge, glowing with some massive attack — whiffs out of the trainyard entirely, leaving nothing but a smoke outline in the air. There is no closing announcement. The music just stops.
The mechanic Carl weaponises twice in five minutes, once by accident and once by design.