It seems the compost I used was more lively than anticipated. There's an earthworm crawling around in there.
It's a decent 12 inch pot, but it's still effectively a limited environment. So I'm not sure if I should leave him in or take him out.
UPDATE: alright. I'll keep him in, cross my fingers, and hope I've pulled in enough of an ecosystem to both sustain him for his expected lifespan, and safely handle the subsequent death and decomposition.
It's an indoors office plant. If it ends up leaving the pot, it'll likely end up getting rolled over by some chair wheels.
Given the soil mix I used, it'll likely be very happy for the rest of its life.