uniac.NodeSpec is the internal base class that both Service and System extend. User code rarely references it directly, but the two hooks it provides are what makes the framework non-magical.
Methods
_uniac_validate()
Called once by load after construction. Walks every class-level annotation across the MRO; for each annotation typed as a Node subclass, asserts that the corresponding instance attribute is set and is the right type. Raises UniacValidationError on mismatch. Records the owner relationship on each owned Node.
_uniac_walk()
Yields the directly-owned Node instances in declaration order. The CLI uses this during uniac deploy to extract the topology.
Why this matters
There is no annotation auto-instantiation. The annotation says “this slot must hold a Node of type X”; your__init__ puts the value there. _uniac_validate enforces the contract loudly at startup so wiring bugs surface immediately instead of at first request.