fix(ack-id): return replyNonce from handshake responses

.changeset/a2a-handshake-return-reply-nonce.md

@@ -0,0 +1,5 @@
+---
+"@agentcommercekit/ack-id": patch
+---
+
+Return the freshly generated `replyNonce` from `createA2AHandshakeMessage` when responding to a handshake, so callers can correlate the next leg.

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

@@ -149,4 +149,19 @@ describe("createA2AHandshakeMessage", () => {
       expect.objectContaining({ kind: "data", data: { jwt: result.sig } }),
     )
   })
+
+  it("returns the fresh replyNonce when requestNonce is provided", async () => {
+    const result = await createA2AHandshakeMessage(
+      "agent",
+      {
+        recipient: userDid,
+        vc: testCredential,
+        requestNonce: "initiator-nonce",
+      },
+      { did: agentDid, jwtSigner },
+    )
+
+    expect(result.nonce).toBe("test-nonce-1234")
+    expect(result.nonce).not.toBe("initiator-nonce")
+  })
 })

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

@@ -122,7 +122,9 @@ export async function createA2AHandshakeMessage(
   return {
     sig: jwt,
     jti,
-    nonce: payload.nonce,
+    // When replying, callers need the freshly generated replyNonce for the next
+    // handshake leg — not the peer's original request nonce in payload.nonce.
+    nonce: payload.replyNonce ?? payload.nonce,
     message,
   }
 }