fix(ack-id): return reply nonce for response handshakes

.changeset/fresh-reply-nonce.md

@@ -0,0 +1,5 @@
+---
+"@agentcommercekit/ack-id": patch
+---
+
+Return the fresh reply nonce from A2A response handshakes so callers can correlate the next handshake leg.

packages/ack-id/src/a2a/sign-message.test.ts

@@ -138,6 +138,20 @@ describe("createA2AHandshakeMessage", () => {
     expect(result.message.role).toBe("agent")
   })
 
+  it("returns the fresh reply nonce when responding to a handshake", async () => {
+    const result = await createA2AHandshakeMessage(
+      "agent",
+      {
+        recipient: userDid,
+        vc: testCredential,
+        requestNonce: "original-nonce",
+      },
+      { did: agentDid, jwtSigner },
+    )
+
+    expect(result.nonce).toBe("test-nonce-1234")
+  })
+
   it("returns the signed JWT in the message data part", async () => {
     const result = await createA2AHandshakeMessage(
       "agent",

packages/ack-id/src/a2a/sign-message.ts

@@ -122,7 +122,7 @@ export async function createA2AHandshakeMessage(
   return {
     sig: jwt,
     jti,
-    nonce: payload.nonce,
+    nonce: payload.replyNonce ?? payload.nonce,
     message,
   }
 }