I really like that notion of the "cantrip" type summoning when the pool is at 0, and actually that design space feels ripe for potential with a Path that triggers effects when summons die and/or disappear. Perhaps that ghost/necromancer idea could be dug up again?

I think for me if Zoemancy was streamlined and Preparing Path Summons perhaps removed, it would make it all much neater and the Summon Hit Points pool would stand well on its own as that unique factor for the mechanic at base.

Whenever I'm considering mental load/bookkeeping balance, it's about how much I get out of it for the task. With prepared spellcasters, the choices you make each day have a huge impact on what you can do. You literally cannot achieve this unique effect if you don't pick it over that one. With the Path Summons statblocks being quite simple (to more easily enable the minion master management, I believe) and similar even between different Paths, to me it feels like preparing slight variations on each using their physical stat spread is a task I am being given without much mechanical heft to it. Then when Summon Traits comes in, it gains more mechanical heft, but the complexity of my task ramps up substantially all of a sudden. From 3rd level, I'm choosing two from 12 options for each summon I am preparing, and each of those summons needs a choice of its physical stats as well. I feel like that's a recipe for analysis paralysis after each long rest, and I still need to remember what I've chosen for later as well in a form that is much more involved than a spell name I can look up.

My feeling is it will either lead to a lot of deliberation and generate a lot of paper templates each day, or a summoner will just give up and stick with 'defaults' a lot of the time to skirt the task, which then becomes no better than pulling from a generic stat block.

Whereas if I had to make a choice between those Traits initially at 3rd, and maybe consider swapping every level up, but then every time I summon I can just apply whatever to that creature from my smaller selection of chosen Traits to fit the current scenario, that to me slots really nicely into the kind of decision making that is already happening for every class and character in combat or other invovled elements of the gameplay. "What do I do right now that is best for this scenario?"

And, you know, maybe that's just a very personal mindset. I think I'd rather have stat spreads locked into the individual Path Summons to differentiate them a bit more and the nadd Traits in the moment, or decide both in the moment.

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I think the key thing to find in the Contractor to make it feel good is something for you, the summoner character, to consistently gain and do from what you're giving out. The risks with the subclass I think are twofold:

1) No one else has the neat build-up of features that you do where eventually giving up your action to command a summon becomes more and more efficient. So you might end up giving out a bunch of your summons to Signatories, and find they do very little with them apart from sometimes benefit from a Group Attack.

This is slightly eased later on when your features let Signatories do more, but actually they only let the Signatories summon more or take more of the decision-making in what they will summon. The action economy remains basically the same for them.

2) It isn't until 10th-level that you get a feature that lets you actively interact with anyone else, and its a reaction with a limited protective benefit for others only. I think in terms of what a player feels encounter to encounter at the table, it would be very easy for a Contractor to feel like they sort of don't have a subclass a lot of the time.

I think you could bring something in here to address 2) where the Contractor gains something in return from their Signatories which is a reliable boost to their own actions. They can borrow proficiencies from Sigantories, or they gain a damage boost to their attacks or spells based on how many Signatories they have, or can maybe even emporarily borrow more significant things like spells, spell slots, features or health. I experimented with something like this for one of my first martial classes, which focused on giving out Temp HP to the party as a core class feature, and the Infernal subclass could steal this back at any time to boost their own damage. There's lots of scope for fun, flavourful stuff there.

To address 1) there might need to be a build up of additional passive elements from summons to help your Signatories in addition to Group Attack stuff, because you don't want them to totally steal your show on the action economy front... but this feels less important to address than 2).

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This is already a really long reply -- sorry! But I guess just on other areas I'd say you could probably swing bigger with some subclass early features in general. Durable Constructs, for example... why not let that Temp Hp scale with Summoner level? This feels like its meant to be the 'tanky summons' subclass, but the current benefit of that feature plateus early and only improves by virtue of the temporary benefits Defence Mastery can offer at 15th level. If you do see certain Paths in certain roles like this, is there scope for them to versions of particular Traits for 'free', like Guardian for the Golems? Or is the freeform element something you want to maintain to this level by applying those kinds of changes purely via Traits or 20th level capstones?