chore(builder): Fix priority fee ordering violations in flashblocks block building

crates/builder/op-rbuilder/src/args/op.rs

@@ -113,6 +113,16 @@ pub struct FlashblocksArgs {
         env = "FLASHBLOCKS_DISABLE_STATE_ROOT"
     )]
     pub flashblocks_disable_state_root: bool,
+
+    /// Whether to enforce priority fee ordering within flashblocks.
+    /// When enabled, transactions that would violate descending priority fee order are skipped
+    /// and deferred to the next flashblock.
+    #[arg(
+        long = "flashblocks.enforce-priority-fee-ordering",
+        default_value = "true",
+        env = "FLASHBLOCKS_ENFORCE_PRIORITY_FEE_ORDERING"
+    )]
+    pub flashblocks_enforce_priority_fee_ordering: bool,
 }
 
 impl Default for FlashblocksArgs {

crates/builder/op-rbuilder/src/flashblocks/config.rs

@@ -33,6 +33,9 @@ pub struct FlashblocksConfig {
 
     /// Should we disable state root calculation for each flashblock
     pub disable_state_root: bool,
+
+    /// Whether to enforce priority fee ordering within flashblocks
+    pub enforce_priority_fee_ordering: bool,
 }
 
 impl Default for FlashblocksConfig {
@@ -43,6 +46,7 @@ impl Default for FlashblocksConfig {
             leeway_time: Duration::from_millis(50),
             fixed: false,
             disable_state_root: false,
+            enforce_priority_fee_ordering: true,
         }
     }
 }
@@ -64,7 +68,17 @@ impl TryFrom<OpRbuilderArgs> for FlashblocksConfig {
 
         let disable_state_root = args.flashblocks.flashblocks_disable_state_root;
 
-        Ok(Self { ws_addr, interval, leeway_time, fixed, disable_state_root })
+        let enforce_priority_fee_ordering =
+            args.flashblocks.flashblocks_enforce_priority_fee_ordering;
+
+        Ok(Self {
+            ws_addr,
+            interval,
+            leeway_time,
+            fixed,
+            disable_state_root,
+            enforce_priority_fee_ordering,
+        })
     }
 }
 

crates/builder/op-rbuilder/src/flashblocks/context.rs

@@ -38,7 +38,7 @@ use reth_revm::{State, context::Block};
 use reth_transaction_pool::{BestTransactionsAttributes, PoolTransaction};
 use revm::{DatabaseCommit, context::result::ResultAndState, interpreter::as_u64_saturated};
 use tokio_util::sync::CancellationToken;
-use tracing::{debug, info, trace};
+use tracing::{debug, info, trace, warn};
 
 use crate::{
     flashblocks::payload::FlashblocksExecutionInfo,
@@ -117,6 +117,8 @@ pub struct OpPayloadBuilderCtx {
     pub address_gas_limiter: AddressGasLimiter,
     /// Unified transaction data store (backrun bundles + resource metering)
     pub tx_data_store: TxDataStore,
+    /// Whether to enforce priority fee ordering within flashblocks
+    pub enforce_priority_fee_ordering: bool,
 }
 
 impl OpPayloadBuilderCtx {
@@ -442,6 +444,14 @@ impl OpPayloadBuilderCtx {
             timestamp: self.attributes().timestamp(),
         };
 
+        // Track the last priority fee to enforce descending order.
+        // Due to a reth bug (https://github.com/paradigmxyz/reth/pull/19940), blocked
+        // transactions are discarded instead of saved, breaking nonce chain tracking.
+        // Later transactions from the same sender can't find the blocked one, so they
+        // get processed as if they have no dependencies and may be yielded out of order.
+        // This check skips out-of-order txs, deferring them to the next flashblock.
+        let mut last_priority_fee: Option<u128> = None;
+
         while let Some(tx) = best_txs.next(()) {
             let interop = tx.interop_deadline();
             let conditional = tx.conditional().cloned();
@@ -462,6 +472,27 @@ impl OpPayloadBuilderCtx {
 
             num_txs_considered += 1;
 
+            // Check priority fee ordering - skip if current tx has higher priority than last.
+            if self.enforce_priority_fee_ordering
+                && let Some(current_priority) = tx.effective_tip_per_gas(base_fee)
+            {
+                if let Some(last_priority) = last_priority_fee
+                    && current_priority > last_priority
+                {
+                    warn!(
+                        target: "payload_builder",
+                        tx_hash = ?tx_hash,
+                        current_priority = current_priority,
+                        last_priority = last_priority,
+                        "Skipping transaction due to priority fee ordering violation"
+                    );
+                    self.metrics.priority_fee_ordering_violations.increment(1);
+                    best_txs.mark_invalid(tx.signer(), tx.nonce());
+                    continue;
+                }
+                last_priority_fee = Some(current_priority);
+            }
+
             let TxData { metering: _resource_usage, backrun_bundles } =
                 self.tx_data_store.get(&tx_hash);
 

crates/builder/op-rbuilder/src/flashblocks/ctx.rs

@@ -88,6 +88,7 @@ impl OpPayloadSyncerCtx {
             max_gas_per_txn: self.max_gas_per_txn,
             address_gas_limiter: AddressGasLimiter::new(GasLimiterArgs::default()),
             tx_data_store: self.tx_data_store,
+            enforce_priority_fee_ordering: true, // default to enabled for tests
         }
     }
 }

crates/builder/op-rbuilder/src/flashblocks/payload.rs

@@ -201,6 +201,7 @@ where
             max_gas_per_txn: self.config.max_gas_per_txn,
             address_gas_limiter: self.address_gas_limiter.clone(),
             tx_data_store: self.config.tx_data_store.clone(),
+            enforce_priority_fee_ordering: self.config.flashblocks.enforce_priority_fee_ordering,
         })
     }
 

crates/builder/op-rbuilder/src/metrics.rs

@@ -181,6 +181,8 @@ pub struct OpRBuilderMetrics {
     pub backrun_bundle_insert_duration: Histogram,
     /// Duration of executing all backrun bundles for a target transaction
     pub backrun_bundle_execution_duration: Histogram,
+    /// Number of transactions skipped due to priority fee ordering violations
+    pub priority_fee_ordering_violations: Counter,
 }
 
 impl OpRBuilderMetrics {

crates/builder/op-rbuilder/src/tests/flashblocks.rs

@@ -228,6 +228,7 @@ async fn test_flashblocks_no_state_root_calculation() -> eyre::Result<()> {
             flashblocks_leeway_time: 100,
             flashblocks_fixed: false,
             flashblocks_disable_state_root: true,
+            flashblocks_enforce_priority_fee_ordering: true,
         },
         ..Default::default()
     };