A JSON Schema is not an AI governance layer

The author argues that JSON Schema validates payload structure but cannot enforce cross-field rules such as an evidence identifier resolving to exactly one provenance entry, so two idiomatic implementations can reach opposite verdicts on identical bytes. Drawing on a bug found in PIC, an open protocol he maintains, he recommends separating schema validation, semantic verification and policy evaluation, and settling ambiguity through shared conformance test vectors. He also warns that trust labels must be derived by the verifier rather than taken from the agent's own payload.