Maintainer vocabulary

This is a pragmatic glossary for maintainers. The normative vocabulary lives in docs/spec/vocabulary.md.

• Contract drift: code and spec disagree.
• Artifact drift: output JSON changes without versioning.
• Spec drift: docs/spec claims behavior not implemented.
• Replay validation: checking a trace satisfies the contract (not rerunning models).
• Canonicalization: stable JSON serialization used for hashing/fingerprints.