I had never really thought about before. I'm trying to work out if this might be more significant.
"They have not told me, Lord. Perhaps Kobat took it onto himself to behave this way."
"I think not. It has occurred to me that your people desired only the death of their chosen assassin."
"The death of Kobat?"
"No, the death of the one they chose to use the weapon." "Who was that, Lord? I've not been told."
"It's unimportant. Do you recall what I said at the time of your ancestor's foolishness?"
It seems that Ix wanted a younger more virile Duncan around when Hwi arrived on the scene. It was a necessary part of their plan to hasten his/Leto’s end by Duncan and Hwi getting it on, and this wouldn't have worked with the older Duncan?
Earlier after the Tleilaxu attack on the way to Onn, there was this exchange about Leto being distracted.
We know the Tleilaxu were helping Ix with the technology for the no-room where Hwi was conceived. Perhaps that’s the extent of it.
"I have been remiss," Leto said. "I should've taught all of you how to detect Face Dancers. It will be corrected now that they grow foolishly bold."
"Why are they so bold?" Idaho asked.
"Perhaps to distract us from something else," Moneo said.
Leto smiled at Moneo. Under the stress of personal threat, the majordomo's mind worked well. He had failed his Lord by mistaking Face Dancer mimics for known Fremen. Now, Moneo felt that his continued service might depend upon those abilities for which the God Emperor had originally chosen him.
"And now we have time to prepare ourselves," Leto said.
"Distract us from what?" Idaho demanded.
"From another plot in which they participate," Leto said. "They think I will punish them severely for this, but the Tleilaxu core remains safe because of you, Duncan."
"They didn't intend to fail here," Idaho said.
"But it was a contingency for which they were prepared," Moneo said.
"They believe I will not destroy them because they hold the original cells of my Duncan Idaho," Leto said. "Do you understand, Duncan?"
"Are they right?" Idaho demanded.
"They approach being wrong," Leto said. He returned his attention to Moneo. "No sign of this event must go with us to Onn. Fresh uniforms, new guards to replace the dead and wounded . . . everything just as it was."
"There are dead among your courtiers, Lord," Moneo said. "Replace them!"
Moneo bowed. "Yes, Lord."
"And send for a new canopy to my cart!"
"As my Lord commands."
Leto backed his cart a few paces away, turned it and headed for the bridge,
calling back to Idaho. "Duncan, you will accompany me."
Slowly at first, reluctance heavy in every movement, Idaho left Moneo and the others, then, increasing his pace, came up beside the cart's open bubble and walked there while staring in at Leto.
"What troubles you, Duncan?" Leto asked.
"Do you really think of me as your Duncan?"
"Of course, just as you think of me as your Leto."
"Why didn't you know this attack was coming?"
"Through my vaunted prescience''"
"Yes!"
"The Face Dancers have not attracted my attention for a long time," Leto said.
"I presume that is changed now?"
"Not to any great degree."
"Why not'?"
"Because Moneo was correct. I will not let myself be distracted."