server/crates/arbiter-client/src/lib.rs

@@ -9,4 +9,4 @@ pub use client::{ArbiterClient, Error};
 pub use storage::{FileSigningKeyStorage, SigningKeyStorage, StorageError};
 
 #[cfg(feature = "evm")]
-pub use wallets::evm::ArbiterEvmWallet;
+pub use wallets::evm::{ArbiterEvmSignTransactionError, ArbiterEvmWallet};

server/crates/arbiter-client/src/wallets/evm.rs

@@ -10,14 +10,48 @@ use tokio::sync::Mutex;
 
 use arbiter_proto::proto::{
     client::{
-        ClientRequest, client_request::Payload as ClientRequestPayload,
+        ClientRequest,
+        client_request::Payload as ClientRequestPayload,
         client_response::Payload as ClientResponsePayload,
+        evm::{
+            self as proto_evm, request::Payload as EvmRequestPayload,
+            response::Payload as EvmResponsePayload,
+        },
     },
-    evm::evm_sign_transaction_response::Result as EvmSignTransactionResult,
+    evm::{
+        EvmSignTransactionRequest,
+        evm_sign_transaction_response::Result as EvmSignTransactionResult,
+    },
+    shared::evm::TransactionEvalError,
 };
 
 use crate::transport::{ClientTransport, next_request_id};
 
+/// A typed error payload returned by [`ArbiterEvmWallet`] transaction signing.
+///
+/// This is wrapped into `alloy::signers::Error::Other`, so consumers can downcast by [`TryFrom`] and
+/// interpret the concrete policy evaluation failure instead of parsing strings.
+#[derive(Debug, thiserror::Error)]
+#[non_exhaustive]
+pub enum ArbiterEvmSignTransactionError {
+    #[error("transaction rejected by policy: {0:?}")]
+    PolicyEval(TransactionEvalError),
+}
+
+impl<'a> TryFrom<&'a Error> for &'a ArbiterEvmSignTransactionError {
+    type Error = ();
+
+    fn try_from(value: &'a Error) -> Result<Self, Self::Error> {
+        if let Error::Other(inner) = value
+            && let Some(eval_error) = inner.downcast_ref()
+        {
+            Ok(eval_error)
+        } else {
+            Err(())
+        }
+    }
+}
+
 pub struct ArbiterEvmWallet {
     transport: Arc<Mutex<ClientTransport>>,
     address: Address,
@@ -96,12 +130,14 @@ impl TxSigner<Signature> for ArbiterEvmWallet {
         transport
             .send(ClientRequest {
                 request_id,
-                payload: Some(ClientRequestPayload::EvmSignTransaction(
+                payload: Some(ClientRequestPayload::Evm(proto_evm::Request {
-                    arbiter_proto::proto::evm::EvmSignTransactionRequest {
+                    payload: Some(EvmRequestPayload::SignTransaction(
-                        wallet_address: self.address.to_vec(),
+                        EvmSignTransactionRequest {
-                        rlp_transaction,
+                            wallet_address: self.address.to_vec(),
-                    },
+                            rlp_transaction,
-                )),
+                        },
+                    )),
+                })),
             })
             .await
             .map_err(|_| Error::other("failed to send evm sign transaction request"))?;
@@ -121,12 +157,21 @@ impl TxSigner<Signature> for ArbiterEvmWallet {
             .payload
             .ok_or_else(|| Error::other("missing evm sign transaction response payload"))?;
 
-        let ClientResponsePayload::EvmSignTransaction(response) = payload else {
+        let ClientResponsePayload::Evm(proto_evm::Response {
+            payload: Some(payload),
+        }) = payload
+        else {
             return Err(Error::other(
                 "unexpected response payload for evm sign transaction request",
             ));
         };
 
+        let EvmResponsePayload::SignTransaction(response) = payload else {
+            return Err(Error::other(
+                "unexpected evm response payload for sign transaction request",
+            ));
+        };
+
         let result = response
             .result
             .ok_or_else(|| Error::other("missing evm sign transaction result"))?;
@@ -136,9 +181,9 @@ impl TxSigner<Signature> for ArbiterEvmWallet {
                 Signature::try_from(signature.as_slice())
                     .map_err(|_| Error::other("invalid signature returned by server"))
             }
-            EvmSignTransactionResult::EvalError(eval_error) => Err(Error::other(format!(
+            EvmSignTransactionResult::EvalError(eval_error) => Err(Error::other(
-                "transaction rejected by policy: {eval_error:?}"
+                ArbiterEvmSignTransactionError::PolicyEval(eval_error),
-            ))),
+            )),
             EvmSignTransactionResult::Error(code) => Err(Error::other(format!(
                 "server failed to sign transaction with error code {code}"
             ))),