diff --git a/crates/fidc-core/src/platform_expr_strategy.rs b/crates/fidc-core/src/platform_expr_strategy.rs
index e7a2d87..f18eaa0 100644
--- a/crates/fidc-core/src/platform_expr_strategy.rs
+++ b/crates/fidc-core/src/platform_expr_strategy.rs
@@ -6158,7 +6158,7 @@ impl PlatformExprStrategy {
     ) -> Result<RuntimeHelperResolution, BacktestError> {
         match helper {
             "factor" => {
-                let key = Self::normalize_runtime_factor_key(&Self::parse_string_or_identifier(
+                let key = Self::normalize_runtime_factor_key(Self::parse_string_or_identifier_ref(
                     args.first().map(String::as_str).unwrap_or_default(),
                 )?);
                 if let Some((field, lookback)) = framework_stock_rolling_factor_requirement(&key) {
@@ -6190,7 +6190,7 @@ impl PlatformExprStrategy {
                 )))
             }
             "day_factor" => {
-                let key = Self::normalize_runtime_factor_key(&Self::parse_string_or_identifier(
+                let key = Self::normalize_runtime_factor_key(Self::parse_string_or_identifier_ref(
                     args.first().map(String::as_str).unwrap_or_default(),
                 )?);
                 Ok(RuntimeHelperResolution::Expression(format!(
@@ -6204,7 +6204,7 @@ impl PlatformExprStrategy {
                         "{helper} expects 2 arguments"
                     )));
                 }
-                let field = Self::parse_string_or_identifier(&args[0])?;
+                let field = Self::parse_string_or_identifier_ref(&args[0])?;
                 let lookback = Self::parse_positive_usize(&args[1])?;
                 let value = self.resolve_rolling_mean(ctx, day, stock, &field, lookback)?;
                 Ok(RuntimeHelperResolution::Number(value))
@@ -6215,7 +6215,7 @@ impl PlatformExprStrategy {
                         "rolling_mean_current expects 2 arguments".to_string(),
                     ));
                 }
-                let field = Self::parse_string_or_identifier(&args[0])?;
+                let field = Self::parse_string_or_identifier_ref(&args[0])?;
                 let lookback = Self::parse_positive_usize(&args[1])?;
                 let value = self.resolve_current_rolling_mean(ctx, day, stock, &field, lookback)?;
                 Ok(RuntimeHelperResolution::Number(value))
@@ -6226,7 +6226,7 @@ impl PlatformExprStrategy {
                         "rolling_max_current expects field and lookback".to_string(),
                     ));
                 }
-                let field = Self::parse_string_or_identifier(&args[0])?;
+                let field = Self::parse_string_or_identifier_ref(&args[0])?;
                 let lookback = Self::parse_positive_usize(&args[1])?;
                 let values =
                     self.resolve_current_rolling_values(ctx, day, stock, &field, lookback)?;
@@ -6239,7 +6239,7 @@ impl PlatformExprStrategy {
                         "rolling_return_stddev_current expects field and return count".to_string(),
                     ));
                 }
-                let field = Self::parse_string_or_identifier(&args[0])?;
+                let field = Self::parse_string_or_identifier_ref(&args[0])?;
                 let return_count = Self::parse_positive_usize(&args[1])?;
                 let values = self.resolve_current_rolling_values(
                     ctx,
@@ -6278,7 +6278,7 @@ impl PlatformExprStrategy {
                         "{helper} expects field and lookback"
                     )));
                 }
-                let field = Self::parse_string_or_identifier(&args[0])?;
+                let field = Self::parse_string_or_identifier_ref(&args[0])?;
                 let lookback = Self::parse_positive_usize(&args[1])?;
                 let values = self.resolve_rolling_values(ctx, day, stock, &field, lookback)?;
                 let value = match helper {
@@ -6297,7 +6297,7 @@ impl PlatformExprStrategy {
                         "pct_change expects field and lookback".to_string(),
                     ));
                 }
-                let field = Self::parse_string_or_identifier(&args[0])?;
+                let field = Self::parse_string_or_identifier_ref(&args[0])?;
                 let lookback = Self::parse_positive_usize(&args[1])?;
                 let values = self.resolve_rolling_values(
                     ctx,
@@ -7083,6 +7083,35 @@ impl PlatformExprStrategy {
         )))
     }
 
+    /// Parse the literal/identifier forms used by runtime helpers without
+    /// allocating a new String on every stock evaluation. The owned parser
+    /// above remains the boundary for helpers that must retain the value.
+    fn parse_string_or_identifier_ref(raw: &str) -> Result<&str, BacktestError> {
+        let trimmed = raw.trim();
+        if trimmed.is_empty() {
+            return Err(BacktestError::Execution(
+                "platform helper argument cannot be empty".to_string(),
+            ));
+        }
+        if let Some(value) = trimmed
+            .strip_prefix('"')
+            .and_then(|value| value.strip_suffix('"'))
+            .or_else(|| {
+                trimmed
+                    .strip_prefix('\'')
+                    .and_then(|value| value.strip_suffix('\''))
+            })
+        {
+            return Ok(value);
+        }
+        if Self::is_expression_identifier(trimmed) {
+            return Ok(trimmed);
+        }
+        Err(BacktestError::Execution(format!(
+            "platform helper expects a factor name or string literal, got {trimmed}"
+        )))
+    }
+
     fn normalize_runtime_factor_key(key: &str) -> String {
         key.trim()
             .trim_matches('"')