eIDAS qualified electronic timestamp (RFC 3161 .tsr) on a Sellat proof, issued in seconds by an EU qualified trust service provider on the EU trusted list. Legal timestamp with the presumption of accuracy of date and integrity of Art. 41.2 eIDAS, recognised across the EU. Use when the date must hold before a court, authority, regulator or auditor. Call it on the proof_id from POST /proofs.