Autonomous AI decisions engage liability — but not through system performance. They become legally attributable only when a competent human authority has documented governance before execution. SOURCE 0 defines this evidentiary threshold as T‑0: the moment where human authorisation is cryptographically sealed by an independent authority. Without a T‑0 seal, an AI act has no author — and under the EU AI Act and the Product Liability Directive 2024, that is a liability without a ceiling.

Trusted Execution Environments seal AI workloads at the silicon level. They do not produce legally opposable evidence. When the operator controls the attestation keys, the Hardware Attestation Report remains endogenous to the system under audit — a structural circularity that no firmware update resolves. SOURCE 0 CERTIFIED closes this gap with an independent Governance Proof Layer: T-0 Capture, SHA-256 hash-chaining, dual-QTSP RFC 3161 timestamping under eIDAS 2, and judicial archiving by a Commissaire de Justice. The result is a Dossier de Réalité Historique directly enforceable across the EU under Brussels I bis — satisfying the ex-ante burden of proof imposed by AI Act Article 99.