The warlords' household courts, from which Juice Box claimed her agents had all been expelled — untruthfully.
Carl recalls that Juice Box said her people "had all been expelled from the courts of the warlords," and realizes on the spot that this was obviously untrue — her agents were still embedded, waiting for The Ceasefire to lapse so they could assassinate leaders under the Leader Kill Rule.
The courts are therefore the strategic terrain of the Ascendency's shadow war: household staffs and retinues around each warlord, dense enough to hide agents in and close enough that a single knife ends a team. It is also why Commander Stockade's cry of "A spy! There's a spy in my midst!" is both wrong about whose spy it was and entirely correct that one existed.
The warlords' inner households, the arena of the Ascendency's espionage.