He did not take action against Project Lawful while Keltham was still in Cheliax because, first, the first news he received of its existence was Cayden Cailean throwing his entire spy network a going-home party; second, because Iomedae’s church concluded that She was subject to non-intervention agreements regarding whatever was going on in Cheliax, and Lastwall does not act in ways that seem likely to be expensive for Iomedae without orders to do so (this particular non-intervention agreement was not so broad as to prohibit Lastwall from doing something on their own initiative, but for Iomedae to tell them this would have been a prohibited intervention); third, because exfiltrating someone from a secret Chelish project is actually just hard; the success of such a mission would have been far from guaranteed even if he had had his usual Chelish assets and orders to do it.
He did not interfere with anything Keltham did after leaving Cheliax because the Communes said that it was not in the interests of Good for Iomedae or Her church to interfere with Keltham in any way, that it was not in the interests of Good for them to know why this was the case, that it was not in the interests of Good for Iomedae to know why this was the case, but She was sure of it nonetheless. And so neither Lastwall nor Iomedae nor her church had any interaction with Keltham that was not on his initiative, even when the rumours out of the City of Brass were that he had somehow acquired an impossible number of Wish diamonds, even when Abrogail Thrune was assassinated by an unknown weapon and not immediately resurrected, even when it began to be whispered in taverns from Lastwall to Lingshen that he and Carissa Sevar and Pilar Pineda would ascend to godhood at the next lunar eclipse, etc., etc., etc.
Especially that last one. In fact, Iomedae’s church had explicit orders via Commune to ignore anything Cayden Cailean was doing, and the tavern rumours sure seemed like that.
He is not, and had never pretended to be, a follower of Iomedae. He had merely offered his services to the god with the highest estimated probability of fixing Hell.
If the tavern rumors are true, that might not be Iomedae any more.
He does not conceive of it as betrayal; nor, indeed, would Iomedae. But when he hears the news from Absalom and the lights of godwar appear in the sky soon after, She cannot command him not to pray.