fix: register SubscriptionFPC in swap flow for sponsored swaps

The SubscriptionFPC was only registered during the drip/claim flow
(registerDripContracts), but sponsored swaps also need it. When a new
account went directly to swap without claiming first, the wallet couldn't
find the SubscriptionFPC artifact in PXE, causing "Contract artifact not
found for class 0x0b1adf2a...".

Now registerSwapContracts also checks and registers the SubscriptionFPC
if configured, following the same pattern as registerDripContracts:
- Checks metadata first to skip if already registered
- Throws if configured FPC is not found on-chain (fail-fast, consistent with drip)
- Registers with artifact and secret key in the same batch

Author: alejoamiras

src/services/contractService.ts

@@ -54,12 +54,21 @@ export async function registerSwapContracts(
   const { TokenContract, TokenContractArtifact } = await import('@aztec/noir-contracts.js/Token');
   const { AMMContract, AMMContractArtifact } = await import('../../contracts/target/AMM');
 
+  // Determine subscription FPC for sponsored swaps
+  const subFPC = network.subscriptionFPC;
+  const fpcAddress = subFPC ? AztecAddressClass.fromString(subFPC.address) : undefined;
+
   // Check which contracts are already registered
-  const [ammMetadata, gregoCoinMetadata, gregoCoinPremiumMetadata] = await wallet.batch([
+  const metadataChecks: { name: 'getContractMetadata'; args: [AztecAddress] }[] = [
     { name: 'getContractMetadata', args: [ammAddress] },
     { name: 'getContractMetadata', args: [gregoCoinAddress] },
     { name: 'getContractMetadata', args: [gregoCoinPremiumAddress] },
-  ]);
+  ];
+  if (fpcAddress) {
+    metadataChecks.push({ name: 'getContractMetadata', args: [fpcAddress] });
+  }
+  const metadataResults = await wallet.batch(metadataChecks);
+  const [ammMetadata, gregoCoinMetadata, gregoCoinPremiumMetadata] = metadataResults;
 
   // Reconstruct contract instances for unregistered contracts
   const [ammInstance, gregoCoinInstance, gregoCoinPremiumInstance] = await Promise.all([
@@ -100,6 +109,23 @@ export async function registerSwapContracts(
     registrationBatch.push({ name: 'registerContract', args: [gregoCoinPremiumInstance, undefined, undefined] });
   }
 
+  // Register subscription FPC for sponsored swaps (if configured and not yet registered)
+  if (subFPC && fpcAddress) {
+    const fpcMetadata = metadataResults[3];
+    if (!fpcMetadata?.result?.instance) {
+      const instance = await node.getContract(fpcAddress);
+      if (!instance) {
+        throw new Error(`Subscription FPC at ${subFPC.address} not found on-chain`);
+      }
+      const secretKey = Fr.fromString(subFPC.secretKey);
+      const { SubscriptionFPCContractArtifact } = await import('@gregojuice/contracts/artifacts/SubscriptionFPC');
+      registrationBatch.push({
+        name: 'registerContract',
+        args: [instance, SubscriptionFPCContractArtifact, secretKey],
+      });
+    }
+  }
+
   // Only call batch if there are contracts to register
   if (registrationBatch.length > 0) {
     await wallet.batch(registrationBatch);