feat: add withdrawal simulation to relayer

packages/relayer/src/services/privacyPoolRelayer.service.ts

@@ -59,6 +59,14 @@ export class PrivacyPoolRelayer {
         throw ZkError.invalidProof();
       }
 
+      // simulate tx before broadcasting
+      const simulationResult = await this.sdkProvider.simulateWithdrawal(req, chainId);
+
+      if (!simulationResult.success) {
+        const simulationError = simulationResult.error || "Unknown simulation failure";
+        throw BlockchainError.txSimulationError(`Relay simulation failed: ${simulationError}`);
+      }
+
       const response = await this.broadcastWithdrawal(req, chainId);
       await this.db.updateBroadcastedRequest(requestId, response.hash);
 

packages/sdk/src/interfaces/contracts.interface.ts

@@ -38,6 +38,12 @@ export interface ContractInteractions {
     scope: Hash,
   ): Promise<TransactionResponse>;
 
+  simulateRelay(
+    withdrawal: Withdrawal,
+    withdrawalProof: WithdrawalProof,
+    scope: Hash
+  ): Promise<{ success: boolean; gasEstimate?: bigint; error?: string }>;
+
   ragequit(
     commitmentProof: CommitmentProof,
     privacyPoolAddress: Address,