How do summons interact with soul-affecting effects?

Question

For reasons of my own, I need a trapped soul for at least a couple of hours. The exact type of soul doesn't matter: so long as I have a soul in a "jar" for, say, 8 hours, I'm good.

I'm a 20th level wizard with "normal" resources.

I'd rather not trap a living creature's soul, so I look for other options and come upon the ability to use Summon Monster to summon a Lemure (or, heck: a Nalfesnhee).

I then use one of the following effects (in all cases, the spell takes the maximum possible effect: the summoned creature fails their save, SR is bypassed, they don't use "this one weird trick", etc.):

• Magic Jar (which could keep a soul in a gem for 1 hour per level, which is plenty)
• Trap the Soul (permanent-ish)
• my Awakened Demilich buddy uses Devour Soul to pull the Lemure's soul into one of its soulgems (at least 24 hours, possibly longer if the demilich doesn't get hungry; side question: can my buddy eat the soul 24+ hours later?)
• or an effect that duplicates one of the above

But, the Lemure was summoned, and summoning only lasts a few rounds. Critically, summoning magic states that:

When the spell ends or is dispelled, a summoned creature is instantly sent back to where it came from, .... A summoned creature also goes away if it is killed or if its hit points drop to 0 or lower, but it is not really dead. It takes 24 hours for the creature to reform, during which time it can’t be summoned again.

So, what happens 20 rounds after the Lemure popped in?

1. The Lemure returns whence it came. What happens to the Magic Jar?
2. The Lemure is stuck where it is.
3. ???

Answer 1

According to James Jacobs, summoned creatures are not unique individuals

Rather, they are "copies" that are idealized incarnations of that creature type. They have no unique particular personality or backstory, and certainly no soul to trap.

Disclaimer: This is not an official ruling

While James Jacob's words have substantial weight as creative director, his views on topics, especially those that have mechanical implications, do not determine RAW. Your GM is free to rule otherwise, although JJ's interpretation is a reasonable one that I recommend using.

What you want is Planar Binding

Planar Binding, unlike the Summon X series, summons actual, distinct entities and not copies. This is why the duration is instantaneous, why Planar Binding summons require negotiations to command, and why they cannot be dispelled. A creature summoned in this way will have a soul.

Aside: If your DM rules that Summon X creatures still have souls, there is a workaround

Simply cast Mount, optionally using Alter Summoned Monster to change its type, and trap the artificial soul of that summon.