feat: Redesign Relayer Binding & Zero-Relayer Semantics (ZK-073)

contracts/privacy_pool/src/core/withdraw.rs

@@ -18,6 +18,7 @@ pub fn execute(
     proof: Proof,
     pub_inputs: PublicInputs,
 ) -> Result<bool, Error> {
+    let invoker_addr = env.invoker();
     // Load and validate pool configuration
     let pool_config = config::load_pool_config(&env, &pool_id)?;
     validation::require_not_paused(&pool_config)?;
@@ -55,6 +56,14 @@ pub fn execute(
     let recipient = address_decoder::decode_address(&env, &pub_inputs.recipient);
     let relayer_opt = address_decoder::decode_optional_relayer(&env, &pub_inputs.relayer);
 
+    // ZK-073: If no relayer is specified (zero-relayer semantics),
+    // enforce that the recipient must be the transaction invoker.
+    if relayer_opt.is_none() {
+        if recipient != invoker_addr {
+            return Err(Error::ZeroRelayerRecipientMismatch);
+        }
+    }
+
     // Step 7: Transfer funds
     transfer_funds(
         &env,

contracts/privacy_pool/src/types/errors.rs

@@ -45,12 +45,14 @@ pub enum Error {
     FeeExceedsAmount = 43,
     /// Relayer address is non-zero but fee is zero
     InvalidRelayerFee = 44,
+    /// Recipient address must be invoker for zero-relayer withdrawals
+    ZeroRelayerRecipientMismatch = 45,
     /// Recipient address is invalid
-    InvalidRecipient = 45,
+    InvalidRecipient = 46,
     /// Pool ID in public inputs does not match the pool being withdrawn from
-    InvalidPoolId = 46,
+    InvalidPoolId = 47,
     /// Denomination in public inputs does not match the pool denomination
-    InvalidDenomination = 47,
+    InvalidDenomination = 48,
 
     // ── Verifying Key ──────────────────────────────────
     /// Verifying key has not been set

sdk/src/test/harness/errors.ts

@@ -82,9 +82,10 @@ export enum ContractErrorCode {
   InvalidProof = 42,
   FeeExceedsAmount = 43,
   InvalidRelayerFee = 44,
-  InvalidRecipient = 45,
-  InvalidPoolId = 46,
-  InvalidDenomination = 47,
+  ZeroRelayerRecipientMismatch = 45,
+  InvalidRecipient = 46,
+  InvalidPoolId = 47,
+  InvalidDenomination = 48,
 
   // Verifying Key
   NoVerifyingKey = 50,
@@ -419,6 +420,24 @@ function classifyByErrorCode(
       };
 
     // Recipient errors
+    case ContractErrorCode.ZeroRelayerRecipientMismatch:
+      return {
+        category: ErrorCategory.RECIPIENT_ERROR,
+        originalMessage: error.message,
+        errorCode,
+        actionableMessage: 'Recipient address must be the transaction invoker for zero-relayer withdrawals.',
+        recommendations: [
+          'When not using a relayer, ensure the withdrawal recipient is your own address',
+          'Verify the recipient address matches the invoker address of the transaction',
+          `Recipient: ${context?.recipient?.slice(0, 16)}...`,
+        ],
+        context: {
+          errorCode,
+          recipient: context?.recipient,
+          relayer: context?.relayer,
+        },
+      };
+
     case ContractErrorCode.InvalidRecipient:
       return {
         category: ErrorCategory.RECIPIENT_ERROR,