diff --git a/crates/fidc-core/src/engine.rs b/crates/fidc-core/src/engine.rs
index a1a6ab5..255834c 100644
--- a/crates/fidc-core/src/engine.rs
+++ b/crates/fidc-core/src/engine.rs
@@ -1935,14 +1935,14 @@ where
                         .ok_or(BacktestError::MissingBenchmark {
                             date: execution_date,
                         })?;
-                let notes = corporate_action_notes.join(" | ");
-                let diagnostics = std::iter::once(format!(
-                    "decision_lag_warmup lag_days={} execution_index={}",
-                    self.config.decision_lag_trading_days, execution_idx
-                ))
-                .chain(broker_diagnostics.into_iter())
-                .collect::<Vec<_>>()
-                .join(" | ");
+                let notes = join_text_parts(corporate_action_notes.into_iter());
+                let diagnostics = join_text_parts(
+                    std::iter::once(format!(
+                        "decision_lag_warmup lag_days={} execution_index={}",
+                        self.config.decision_lag_trading_days, execution_idx
+                    ))
+                    .chain(broker_diagnostics.into_iter()),
+                );
                 let holdings_for_day = portfolio.holdings_summary(execution_date);
                 let holding_start = result.daily_holdings.len();
                 let holding_count = holdings_for_day.len();
@@ -3012,17 +3012,17 @@ where
                     .ok_or(BacktestError::MissingBenchmark {
                         date: execution_date,
                     })?;
-            let notes = corporate_action_notes
-                .into_iter()
-                .chain(decision.notes.into_iter())
-                .collect::<Vec<_>>()
-                .join(" | ");
-            let diagnostics = decision
-                .diagnostics
-                .into_iter()
-                .chain(broker_diagnostics.into_iter())
-                .collect::<Vec<_>>()
-                .join(" | ");
+            let notes = join_text_parts(
+                corporate_action_notes
+                    .into_iter()
+                    .chain(decision.notes.into_iter()),
+            );
+            let diagnostics = join_text_parts(
+                decision
+                    .diagnostics
+                    .into_iter()
+                    .chain(broker_diagnostics.into_iter()),
+            );
             let holdings_for_day = portfolio.holdings_summary(execution_date);
             let holding_start = result.daily_holdings.len();
             let holding_count = holdings_for_day.len();
@@ -4303,6 +4303,22 @@ fn futures_limit_satisfied(side: OrderSide, price: f64, limit_price: Option<f64>
     }
 }
 
+fn join_text_parts<I>(parts: I) -> String
+where
+    I: IntoIterator<Item = String>,
+{
+    let mut iterator = parts.into_iter();
+    let Some(first) = iterator.next() else {
+        return String::new();
+    };
+    let mut result = first;
+    for part in iterator {
+        result.push_str(" | ");
+        result.push_str(&part);
+    }
+    result
+}
+
 fn futures_cancel_report(
     date: NaiveDate,
     order: FuturesOpenOrder,
@@ -4392,6 +4408,15 @@ mod tests {
 
     const SYMBOL: &str = "000001.SZ";
 
+    #[test]
+    fn join_text_parts_matches_vec_join_contract() {
+        assert_eq!(super::join_text_parts(Vec::<String>::new()), "");
+        assert_eq!(
+            super::join_text_parts(vec!["a".to_string(), "".to_string(), "c".to_string()]),
+            "a |  | c"
+        );
+    }
+
     #[derive(Debug)]
     struct BuyWhenDecisionDateStrategy {
         decision_date: NaiveDate,