EVE CoreGuard is a governance runtime that enforces policies on AI systems before actions execute. It intercepts proposed AI actions and evaluates them against a governance corpus using deterministic rules in under one millisecond, deciding which actions are permitted and blocking unauthorized ones pre-execution. The software enforces authorization through three layers: immutable pre-execution rules, governed inference routing for model selection and context allocation, and cryptographic authority chains for tamper-evident audit records. Each decision generates an ECDSA P-384-signed certificate with hash-chained provenance for offline verification. EVE CoreGuard deploys as a sidecar proxy, REST API, or SDK integration. It includes domain-specific governance corpora for lending, healthcare, trading, and enterprise security, encoding regulatory requirements as structural rules applied during evaluation.