jcp/jcp-rs/crates/jcp-x402/examples/pay.rs

@@ -8,7 +8,7 @@
 
 use ed25519_dalek::SigningKey;
 use jcp_schema::{Did, Funds, Verdict};
-use jcp_x402::{ingest_requirements, Gated, X402Profile, X402Requirements};
+use jcp_x402::{ingest_requirements, Gated, X402Profile, X402Requirements, X402Settlement};
 use serde_json::json;
 
 fn main() {
@@ -64,7 +64,42 @@ fn main() {
     let eurc = X402Requirements { asset: "EURC".into(), max_amount: 100, ..req.clone() };
     println!("charge in EURC (grant is USDC)     → {}", verdict(&profile.authorize(&eurc, 1)));
 
-    // 6. Every decision sealed a JCR-1 receipt that verifies under the steward
+    // 6. THE COUPLING. The host settles the authorized charge on chain and gets
+    //    back a transaction; the meter reports what the paid compute actually
+    //    consumed. Sealing them together produces the artifact neither side has:
+    //    the payment rail knows the transaction but not the energy, an energy
+    //    meter knows the joules but not the transaction.
+    let settled = X402Settlement {
+        transaction: Some("0xdeadbeefcafe".into()),
+        network: "base".into(),
+        payer: Some("0xAgentWallet".into()),
+    };
+    let measured_uj = 5_812; // what the meter read, not the 6000 µJ estimate
+    let g = profile.seal_settlement(&req, &settled, measured_uj);
+    println!("\nsettled {} → sealed {}", settled.transaction.as_deref().unwrap_or("-"), verdict(&g));
+
+    //    A third party verifies the binding without trusting the gateway: it
+    //    recomputes the coupling id from the settlement record it holds and
+    //    checks it against the receipt's payload_hash (jcp/2, SPEC §8).
+    let core = jcp_receipt::extract(&g.receipt, profile.steward(), &profile.steward_pubkey())
+        .expect("settlement receipt verifies");
+    let expected = settled.coupling_id(&req.resource, measured_uj).to_hex();
+    println!(
+        "  coupling verified: {}  (tx + {} µJ bound into payload_hash {}…)",
+        core.payload_hash.as_deref() == Some(expected.as_str()),
+        measured_uj,
+        &expected[..16]
+    );
+
+    //    Re-pointing the receipt at a different transaction — or a different
+    //    energy figure — yields a different id, so the binding cannot be moved.
+    let other = X402Settlement { transaction: Some("0xfeed".into()), ..settled.clone() };
+    println!(
+        "  re-point to another tx → id matches: {}",
+        core.payload_hash.as_deref() == Some(other.coupling_id(&req.resource, measured_uj).to_hex().as_str())
+    );
+
+    // 7. Every decision sealed a JCR-1 receipt that verifies under the steward
     //    key — a third party trusts the decision, not the gateway.
     let steward = profile.steward().to_string();
     let pk = profile.steward_pubkey();