Review comments

crates/driver/src/domain/competition/mod.rs

@@ -89,7 +89,7 @@ impl Competition {
     pub async fn solve(&self, auction: &Auction) -> Result<Option<Solved>, Error> {
         if self.settle_queue.capacity() == 0 {
             tracing::warn!("settlement queue is full; auction is rejected");
-            return Err(Error::SubmissionError);
+            return Err(Error::SettlementQueueIsFull);
         }
 
         let liquidity = match self.solver.liquidity() {
@@ -369,30 +369,30 @@ impl Competition {
                 submission_deadline,
                 response_sender,
             } = request;
-            if self.eth.current_block().borrow().number >= submission_deadline {
-                if let Err(err) = response_sender.send(Err(DeadlineExceeded.into())) {
-                    tracing::error!(
-                        ?err,
-                        "settle deadline exceeded. unable to return a response"
-                    );
+            let solver = self.solver.name().as_str();
+            async {
+                if self.eth.current_block().borrow().number >= submission_deadline {
+                    if let Err(err) = response_sender.send(Err(DeadlineExceeded.into())) {
+                        tracing::warn!(
+                            ?err,
+                            "settle deadline exceeded. unable to return a response"
+                        );
+                    }
+                    return;
                 }
-                continue;
-            }
-            let solver = self.solver.name().to_string();
-            let result = async {
+
                 observe::settling();
                 let result = self
                     .process_settle_request(auction_id, solution_id, submission_deadline)
                     .await;
                 observe::settled(self.solver.name(), &result);
-                result
-            }
-            .instrument(tracing::info_span!("/settle", solver, auction_id))
-            .await;
 
-            if let Err(err) = response_sender.send(result) {
-                tracing::error!(?err, "Failed to send /settle response");
+                if let Err(err) = response_sender.send(result) {
+                    tracing::error!(?err, "Failed to send /settle response");
+                }
             }
+            .instrument(tracing::info_span!("/settle", solver, auction_id))
+            .await
         }
     }
 
@@ -586,4 +586,6 @@ pub enum Error {
     Solver(#[from] solver::Error),
     #[error("failed to submit the solution")]
     SubmissionError,
+    #[error("too many pending settlements for the same solver")]
+    SettlementQueueIsFull,
 }

crates/driver/src/infra/api/error.rs

@@ -83,6 +83,7 @@ impl From<competition::Error> for (hyper::StatusCode, axum::Json<Error>) {
             competition::Error::DeadlineExceeded(_) => Kind::DeadlineExceeded,
             competition::Error::Solver(_) => Kind::SolverFailed,
             competition::Error::SubmissionError => Kind::FailedToSubmit,
+            competition::Error::SettlementQueueIsFull => Kind::SolverFailed,
         };
         error.into()
     }

crates/driver/src/infra/observe/mod.rs

@@ -368,6 +368,7 @@ fn competition_error(err: &competition::Error) -> &'static str {
         competition::Error::Solver(solver::Error::Deserialize(_)) => "SolverDeserializeError",
         competition::Error::Solver(solver::Error::Dto(_)) => "SolverDtoError",
         competition::Error::SubmissionError => "SubmissionError",
+        competition::Error::SettlementQueueIsFull => "SettlementQueueIsFull",
     }
 }