This is Pillar 1. Your prompt is signed on this device (a key generated in your browser) before it leaves. A measured binder runs it through the model and returns a signed answer cryptographically bound to your prompt — you get a green light if it verifies, a check-engine light if anything was altered. Type /evidence for your session proof.
Signed with WebCrypto P-256 in your browser. Click any status light for the full proof — origin, model identity, prompt↔output binding, Merkle root, anchor.