Verified Failover: Contract-Aware Validation for Multi-Provider LLM Architectures (CANON Engine)

Demonstrates that standard HTTP 200-based failover in multi-provider LLM systems misses entire categories of semantic failures. Analysis of 80,000 production API traces across 13 providers and 33 models reveals 6 classes of silent failures undetectable by transport-level checks: empty responses with 200, semantic drift, cost spikes, schema mismatch, identity substitution, and unannounced model upgrades. Proposes CANON (Contract-Aware Negotiation) — a 6-dimension contract validation engine that verifies failover responses against semantic contracts before acceptance. Dimensions: schema conformance, cost bounds, identity verification, semantic consistency, format compliance, and latency bounds. This approach transforms failover from transport-level retry to semantic-level verification, preventing wrong-answer propagation in autonomous AI agent pipelines.