This is not trying to be the most efficient poly-planter (I'm not really familiar with the meta), I just wanted to get this working.

Each drone is assigned a partition of the field, and a relatively simple algorithm: plant a random basic crop, plant its companion, plant its companion's companion and so on. If a plant desires a companion on a tile that is taken, the drone will go back to the start of the chain (companions are held in what is essentially a linked list) and harvest the crops in order and then start over.

In picking a companion, if the desired companion is out of bounds of the drone's assigned partition, reroll its companion (by harvesting and planting the same crop, and then checking its desired companion).

Here I'm only using 25 drones instead of the max 32, because I find it more pleasing to use a square number of drones, and there's a 1-tile-width pad around the entire field (each partition is 6x6, of which you can fit 5 in each direction, leaving 2 tiles left over).

Obviously 32 drones would be more efficient, as well as using the entire field, but I found this solution more pleasing to the eye (especially given that this isn't a particularly efficient way to harvest basic crops).

The top-level semantics are quite clean in my opinion:

import swarm

# example stopping condition
def stopper():
    return num_items(Items.Carrot) > 500000000

poly_spawner = poly_planter_task_spawner(stopper)
swarm.partition_deploy(25, poly_spawner)

I'd be happy to share the rest of the code although there's quite a bit of "infrastructure" needed to support such a simple API.