What would be the most pain-free way of migrating from a monolithic stack to smaller service-based stacks? Ie. Is there an easy way to migrate state if I am already making use of a parent relationship for the "services" which I want to pull out of a monolithic deployment?

It's maybe not as easy as you'd like, but one tip that's helped me is that if you export the state to a JSON file, each resource has its

id

listed, which saves me the effort of having to lookup what format each resource expects its import ID to be in and what the values are. This works for both (terraform => pulumi) and (pulumi => pulumi) stack moving

Ty for the tip!