Tradition that armies halt during council, with no actual rule stopping a move while warlords are trapped.
Odette lays out the rule and its hole in the same breath: all hostilities are supposed to stop during council, and traditionally the armies halt their marches and attacks. But there is no rule against anyone making a move while the warlords are otherwise occupied. With the stakes so high, she can't help but wonder if anyone is planning a surprise action while they're all stuck in here.
She is right to wonder. Princess Vinata whispers to Carl that his move may be happening right now while they're up here, and that the Blood Sultanate is expecting it. Carl, for his part, notes with quiet satisfaction that the meeting has run far longer than he anticipated—"which was good."
The customary ceasefire that is not actually enforceable, and which both sides are exploiting.