He doesn't swim naked, so he takes the summon anyway.
"Hollow wands exist. It's the weight rather than strictly the size that holds in that case."
"Okay. But there is a limit to how dense I can make a specific kind of metal while it retains the various features of the metal that might be important. So I don't know how far that gets me."
"Well, which would you prefer: taking days or weeks to develop the perfect shield-cloak, or venturing out with the one you have?" inquires Dalvor.
"Does it seem likely that if the evil aliens discover that they can't kill me they will keep me stunned indefinitely?"
"It's possible," he says. "They haven't yet been observed to capture anyone they couldn't kill. But we can send an escort."
"I mean, I might have a way around that sans escort if someone would like to help me test it out. I have no idea why I'm here and presumably you don't want to be rid of me as long as I am open to helping you with your evil aliens, but if summoning is working as normal, I can be dismissed at arbitrary range and re-summoned. Unfortunately, if summoning is not working as normal - if I am here now for some reason other than 'nobody else made that kind of shield flat on the ground in sufficient size before' - I have no way to predict accurately in what respects it's different. So testing would involve risking stranding another daeva here indefinitely."
"I am very interested to know how you can be dismissed at arbitrary range and re-summoned," says Dalvor. "I don't wish to strand another daeva here indefinitely, but if it would help win the war without significant risk of the stranded person causing more trouble than they solved, I'm not opposed to trying."
"I'm opposed to trying. Daeva are in general very dangerous, I don't object to the use of bindings for temporary summons but it's a hell of a thing to do to a person who's going to be around forever, and the first thing they'll try if it turns out they object to being stranded is killing their summoner on the assumption that the summoner must not be really trying to dismiss them."
"I'm sure I will have no trouble finding a prospective summoner who would willingly assume that risk, if the reward is potentially being permanently rid of the Enemy. What exactly do you propose to test, and what exactly are your objections to it?"
"...I was thinking that someone could summon and dismiss another daeva and demonstrate that summonings and dismissals are both working the way that I expect them to, if they are, without risking sending me home and not being able to get me back. But. Daeva are really really immortal. If something goes wrong they will either be bound, forever, which is not all right as a permanent condition, or they will be loose and likely pissed off. I guess you could keep stunning one around the clock forever but that's not something I want to do to an innocent bystander either. I can think of one angel who might be okay with being stranded if nothing significant has changed in the last hundred fifty years, and I think they'd be okay with it specifically because they've always wanted to meet aliens."
"I don't know what precisely you mean by bound; I concede that it may very well not be all right as a permanent condition. However, neither is death. I am deeply, deeply tired of the rate at which my friends and subjects keep dying. My goal is to end this war, and in that I beg your assistance." He glances aside for a moment at some subtle signal. "Yes, Faidre?"
"Cam claims to be able to trivially destroy the planet. I judge it not unlikely," he says.
Returning his attention to Cam, he continues, "So perhaps the risks of a test are too great; very well. What can be done to make progress toward saving the world safely and expediently?"
"I don't know if I could trivially destroy this planet because it's a weird planet and I'm not about to try it and see. I'm... still uncomfortable with bringing a non-immortal escort along but I suppose the situation is in fact lethally urgent for exactly the sort of person you'd be drawing the escort from. I can at least give them shield suits, I guess. I'll want to try using my computer to try to decipher their language if they have one and you don't already have someone who can translate."
"No one has ever made much progress learning the language of the Enemy from the fragments we hear," says the king. "Azair?"
"If they do seem to have a language and you don't know how it works it might be worth sending a drone - that's a little flying non-person device that can sort-of-kind-of-think - to listen in on them and see where I can get with that. I mean, they might just blow it up but a drone will be less inconvenienced than a person by extra weight from shields."
"Reasonable," says the king. "Then if we're decided on sending you to the edge now, the last question before you leave is: how will we dismiss and resummon you if you appear to have been captured irretrievably by the Enemy?"
"Summoner concentrates on wanting rid of me for about a minute. Here is a circle that will get me, personally, unbound, if drawn on the floor with room for me in the middle of it. Don't fuck with the design." He produces a paper. "You may want to give me a few minutes before panicking in case you happen to finish the circle while I'm in the shower or something."
"Thank you," says the king. "I leave you in Azair's hands. Faidre, take charge of your grandchildren; none of them may go along."
"I should warn you all before anybody draws that. And because one of you has already performed a summoning. Under the system I am familiar with - which does not include strange physics or evil aliens or anything like that - people who summon daeva become, on their deaths, daeva themselves. The alternative - again under the system I'm familiar with - is worse, but I don't know how any of this interacts with whatever you've got going on."
"Normally what people become on their deaths is dead," says Dalvor. "Indestructibility and world-shaking powers seem preferable."