Nice practical framing. I’m biased because this maps to patterns I’m building around nxusKit SDK, but the design point stands on its own: a builder/chain makes each guard independently testable and makes the chain itself a reviewable artifact.
In practice, I’d map the stages as structured-output extraction -> deterministic rule checks -> repair/escalation packet. Python is the most natural place for a fluent .add() version; Rust and Go can do the same with trait/interface stages, just with less syntactic fluidity.
The production fields I’d add per stage are guard id/version, observed facts, authority boundary, verdict, and trace id, so the pipeline is not only reusable but auditable.