test(mcp): simulate real library shapes in legacy paid_call tests

tests/mcp.test.ts

@@ -24,7 +24,12 @@ describe('BazaarMcpServer — server identity', () => {
 
 describe('BazaarMcpServer', () => {
   it('should map signature expiration ledger error to ERR_EXPIRED_AUTHORISATION', async () => {
-    const mockFetch = vi.fn().mockRejectedValue(new Error('Transaction signature expired. Signature expiration ledger 123 is less than current ledger 125'));
+    // What the payment client actually surfaces: @x402/fetch rethrows a scheme
+    // failure as `Failed to create payment payload: <cause>`, and the cause for a
+    // lapsed signature is the SDK's own `The transaction has expired`
+    // (@stellar/stellar-sdk lib/webauth/utils.js).
+    const expired = new Error('Failed to create payment payload: The transaction has expired');
+    const mockFetch = vi.fn().mockRejectedValue(expired);
     const server = new BazaarMcpServer({ fetchWithPayment: mockFetch, paidCallAllowlist: ['example.com'] });
 
     // The SDK server doesn't expose the router directly without a client, but we can test the handlePaidCallError method directly,
@@ -80,11 +85,15 @@ describe('BazaarMcpServer', () => {
   });
 
   it('should map 402 rejected error to ERR_PAYMENT_REJECTED', async () => {
-    const mockFetch = vi.fn().mockResolvedValue({
-      ok: false,
-      status: 402,
-      text: async () => 'Payment Required'
-    });
+    // fetchWithPayment does not throw on a rejected payment: it pays, retries,
+    // and hands back the seller's second response, so this is a real Response
+    // carrying the x402 error body rather than a hand-rolled object.
+    const mockFetch = vi.fn().mockResolvedValue(
+      new Response(
+        JSON.stringify({ x402Version: 1, error: 'Payment failed: signature invalid' }),
+        { status: 402, headers: { 'Content-Type': 'application/json' } },
+      ),
+    );
 
     const server = new BazaarMcpServer({ fetchWithPayment: mockFetch, paidCallAllowlist: ['example.com'] });
 
@@ -111,11 +120,19 @@ describe('BazaarMcpServer', () => {
   });
 
   it('should return successfully on a successful call', async () => {
-    const mockFetch = vi.fn().mockResolvedValue({
-      ok: true,
-      status: 200,
-      text: async () => JSON.stringify({ success: true, data: "hello" })
-    });
+    // A settled call is a real Response whose body is the resource's payload and
+    // whose X-PAYMENT-RESPONSE header carries the seller's settlement echo; the
+    // ledger decodes that header, so a stand-in without Headers would skip the
+    // only code path that reads it.
+    const settlement = Buffer.from(
+      JSON.stringify({ success: true, network: 'stellar:testnet' }),
+    ).toString('base64url');
+    const mockFetch = vi.fn().mockResolvedValue(
+      new Response(JSON.stringify({ success: true, data: 'hello' }), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json', 'X-PAYMENT-RESPONSE': settlement },
+      }),
+    );
 
     const server = new BazaarMcpServer({ fetchWithPayment: mockFetch, paidCallAllowlist: ['example.com'] });