dex: avoid chain halts in case of arb failures (#3897)

In #3893 we encountered a bug in arb search logic that caused a chain
halt. While that bug shouldn't exist, it also shouldn't have stopped the
entire chain. Rather, we should continue operating without performing
arbitrage.

This commit does not fix the bug in #3893, but it does mean that the
effect of that bug is just to stop arb from occurring rather than
halting the chain.

crates/core/component/dex/src/component/dex.rs

@@ -4,7 +4,8 @@ use anyhow::Result;
 use async_trait::async_trait;
 use cnidarium::{StateRead, StateWrite};
 use cnidarium_component::Component;
-use penumbra_asset::{asset, STAKING_TOKEN_ASSET_ID};
+use penumbra_asset::{asset, Value, STAKING_TOKEN_ASSET_ID};
+use penumbra_num::Amount;
 use penumbra_proto::{StateReadProto, StateWriteProto};
 use penumbra_sct::component::clock::EpochRead;
 use tendermint::v0_37::abci;
@@ -68,7 +69,7 @@ impl Component for Dex {
         }
 
         // Then, perform arbitrage:
-        let arb_burn = state
+        let arb_burn = match state
             .arbitrage(
                 *STAKING_TOKEN_ASSET_ID,
                 vec![
@@ -100,7 +101,18 @@ impl Component for Dex {
                 ],
             )
             .await
-            .expect("must be able to process arbitrage");
+        {
+            Ok(v) => v,
+            Err(e) => {
+                // The arbitrage search should not error, but if it does, we should
+                // simply not perform arbitrage, rather than halting the entire chain.
+                tracing::warn!(?e, "error processing arbitrage, this is a bug");
+                Value {
+                    amount: Amount::zero(),
+                    asset_id: *STAKING_TOKEN_ASSET_ID,
+                }
+            }
+        };
 
         if arb_burn.amount != 0u64.into() {
             // TODO: hack to avoid needing an asset cache for nice debug output