Versioning, effective dates and drift
A compiled rule is a durable artifact. Most of this is unglamorous and most systems get it wrong in the same places.
Immutable versions. Never edit a deployed artifact; v4 is a new object. Content-address it alongside a sequence number: the hash goes in decision logs, the number is what humans discuss. And pin rather than float — if your engine resolves "latest" at evaluation time, two identical requests either side of a deploy give different answers with no local evidence of why.
The version is a required field in every decision record. A decision without its artifact version is unexplainable and therefore, for audit purposes, did not happen.
A policy is agreed in March, effective from 1 January, deployed in April. How many distinct dates does your artifact need?
The rest of this lesson unlocks when you commit above.