diff --git a/crates/fidc-core/src/data.rs b/crates/fidc-core/src/data.rs
index 1cbb087..3f89d96 100644
--- a/crates/fidc-core/src/data.rs
+++ b/crates/fidc-core/src/data.rs
@@ -402,6 +402,23 @@ impl SymbolPriceSeries {
         Some(sum / lookback as f64)
     }
 
+    fn decision_close_rolling_average(&self, date: NaiveDate, lookback: usize) -> Option<f64> {
+        if lookback == 0 {
+            return None;
+        }
+        let end = self.decision_end_index(date)?;
+        if end == 0 {
+            return None;
+        }
+        let start = end.saturating_sub(lookback);
+        let count = end.saturating_sub(start);
+        if count == 0 {
+            return None;
+        }
+        let sum = self.prev_close_prefix[end] - self.prev_close_prefix[start];
+        Some(sum / count as f64)
+    }
+
     fn decision_volume_moving_average(&self, date: NaiveDate, lookback: usize) -> Option<f64> {
         if lookback == 0 {
             return None;
@@ -415,6 +432,23 @@ impl SymbolPriceSeries {
         Some(sum / lookback as f64)
     }
 
+    fn decision_volume_rolling_average(&self, date: NaiveDate, lookback: usize) -> Option<f64> {
+        if lookback == 0 {
+            return None;
+        }
+        let end = self.decision_end_index(date)?;
+        if end == 0 {
+            return None;
+        }
+        let start = end.saturating_sub(lookback);
+        let count = end.saturating_sub(start);
+        if count == 0 {
+            return None;
+        }
+        let sum = self.volume_prefix[end] - self.volume_prefix[start];
+        Some(sum / count as f64)
+    }
+
     fn end_index(&self, date: NaiveDate) -> Option<usize> {
         match self.dates.binary_search(&date) {
             Ok(idx) => Some(idx + 1),
@@ -827,6 +861,71 @@ impl DataSet {
             .and_then(|series| series.decision_volume_moving_average(date, lookback))
     }
 
+    pub fn factor_numeric_value(
+        &self,
+        date: NaiveDate,
+        symbol: &str,
+        field: &str,
+    ) -> Option<f64> {
+        self.factor(date, symbol)
+            .and_then(|snapshot| factor_numeric_value(snapshot, field))
+    }
+
+    pub fn factor_moving_average(
+        &self,
+        date: NaiveDate,
+        symbol: &str,
+        field: &str,
+        lookback: usize,
+    ) -> Option<f64> {
+        if lookback == 0 {
+            return None;
+        }
+        let dates = self.calendar.trailing_days(date, lookback);
+        if dates.is_empty() {
+            return None;
+        }
+        let mut sum = 0.0_f64;
+        let mut count = 0usize;
+        for trading_day in dates {
+            let snapshot = self.factor(trading_day, symbol)?;
+            let value = factor_numeric_value(snapshot, field)?;
+            sum += value;
+            count += 1;
+        }
+        if count == 0 {
+            None
+        } else {
+            Some(sum / count as f64)
+        }
+    }
+
+    pub fn market_decision_numeric_moving_average(
+        &self,
+        date: NaiveDate,
+        symbol: &str,
+        field: &str,
+        lookback: usize,
+    ) -> Option<f64> {
+        match field {
+            "close" | "prev_close" | "stock_close" | "price" => {
+                self.market_series_by_symbol
+                    .get(symbol)
+                    .and_then(|series| series.decision_close_rolling_average(date, lookback))
+            }
+            "volume" | "stock_volume" => {
+                self.market_series_by_symbol
+                    .get(symbol)
+                    .and_then(|series| series.decision_volume_rolling_average(date, lookback))
+            }
+            "open" => self.market_moving_average(date, symbol, lookback, PriceField::Open),
+            "last" | "last_price" => {
+                self.market_moving_average(date, symbol, lookback, PriceField::Last)
+            }
+            other => self.factor_moving_average(date, symbol, other, lookback),
+        }
+    }
+
     pub fn market_moving_average(
         &self,
         date: NaiveDate,
@@ -981,6 +1080,19 @@ fn read_factors(path: &Path) -> Result<Vec<DailyFactorSnapshot>, DataSetError> {
     Ok(snapshots)
 }
 
+fn factor_numeric_value(snapshot: &DailyFactorSnapshot, field: &str) -> Option<f64> {
+    match field {
+        "market_cap" | "market_cap_bn" => Some(snapshot.market_cap_bn),
+        "free_float_cap" | "free_float_market_cap" | "free_float_cap_bn" => {
+            Some(snapshot.free_float_cap_bn)
+        }
+        "pe_ttm" => Some(snapshot.pe_ttm),
+        "turnover_ratio" => snapshot.turnover_ratio,
+        "effective_turnover_ratio" => snapshot.effective_turnover_ratio,
+        other => snapshot.extra_factors.get(other).copied(),
+    }
+}
+
 fn read_candidates(path: &Path) -> Result<Vec<CandidateEligibility>, DataSetError> {
     let rows = read_rows(path)?;
     let mut snapshots = Vec::new();
diff --git a/crates/fidc-core/src/platform_expr_strategy.rs b/crates/fidc-core/src/platform_expr_strategy.rs
index 4f6d23a..13b910a 100644
--- a/crates/fidc-core/src/platform_expr_strategy.rs
+++ b/crates/fidc-core/src/platform_expr_strategy.rs
@@ -107,6 +107,7 @@ struct ProjectedExecutionFill {
 
 #[derive(Debug, Clone)]
 struct DayExpressionState {
+    date: NaiveDate,
     signal_close: f64,
     benchmark_close: f64,
     benchmark_ma_short: f64,
@@ -701,6 +702,7 @@ impl PlatformExprStrategy {
         let is_month_end = next_day.month() != date.month();
 
         Ok(DayExpressionState {
+            date,
             signal_close,
             benchmark_close,
             benchmark_ma_short,
@@ -1032,6 +1034,7 @@ impl PlatformExprStrategy {
 
     fn eval_dynamic(
         &self,
+        ctx: &StrategyContext<'_>,
         expr: &str,
         day: &DayExpressionState,
         stock: Option<&StockExpressionState>,
@@ -1039,10 +1042,11 @@ impl PlatformExprStrategy {
     ) -> Result<Dynamic, BacktestError> {
         let mut scope = self.eval_scope(day, stock, position);
         let normalized_expr = Self::normalize_expr(expr);
+        let expanded_expr = self.expand_runtime_helpers(ctx, day, stock, &normalized_expr)?;
         let prelude_declared_identifiers = Self::declared_prelude_identifiers(&self.config.prelude);
         if let Some(item) = stock {
             let reserved_names = Self::reserved_scope_names();
-            for identifier in Self::extract_identifier_candidates(&normalized_expr) {
+            for identifier in Self::extract_identifier_candidates(&expanded_expr) {
                 if reserved_names.contains(identifier.as_str())
                     || prelude_declared_identifiers.contains(&identifier)
                     || !day.available_factor_names.contains(&identifier)
@@ -1073,7 +1077,7 @@ impl PlatformExprStrategy {
         if let Some(alias_prelude) = factor_alias_prelude {
             script_parts.push(alias_prelude);
         }
-        script_parts.push(normalized_expr);
+        script_parts.push(expanded_expr);
         let script = script_parts.join("\n");
         self.engine
             .eval_with_scope::<Dynamic>(&mut scope, &script)
@@ -1084,6 +1088,273 @@ impl PlatformExprStrategy {
         Self::rewrite_ternary(expr.trim())
     }
 
+    fn expand_runtime_helpers(
+        &self,
+        ctx: &StrategyContext<'_>,
+        day: &DayExpressionState,
+        stock: Option<&StockExpressionState>,
+        expr: &str,
+    ) -> Result<String, BacktestError> {
+        let mut output = String::with_capacity(expr.len());
+        let mut cursor = 0usize;
+        while cursor < expr.len() {
+            let Some(ch) = expr[cursor..].chars().next() else {
+                break;
+            };
+            if !(ch == '_' || ch.is_ascii_alphabetic()) {
+                output.push(ch);
+                cursor += ch.len_utf8();
+                continue;
+            }
+            let ident_start = cursor;
+            cursor += ch.len_utf8();
+            while cursor < expr.len() {
+                let Some(next) = expr[cursor..].chars().next() else {
+                    break;
+                };
+                if next == '_' || next.is_ascii_alphanumeric() {
+                    cursor += next.len_utf8();
+                } else {
+                    break;
+                }
+            }
+            let ident = &expr[ident_start..cursor];
+            let whitespace_start = cursor;
+            while cursor < expr.len() {
+                let Some(next) = expr[cursor..].chars().next() else {
+                    break;
+                };
+                if next.is_whitespace() {
+                    cursor += next.len_utf8();
+                } else {
+                    break;
+                }
+            }
+            let Some(next) = expr[cursor..].chars().next() else {
+                output.push_str(&expr[ident_start..cursor]);
+                break;
+            };
+            if next != '(' || !matches!(ident, "factor" | "day_factor" | "rolling_mean" | "sma") {
+                output.push_str(&expr[ident_start..cursor]);
+                continue;
+            }
+            let Some(close_idx) = Self::find_matching_paren(expr, cursor) else {
+                return Err(BacktestError::Execution(format!(
+                    "platform helper call not closed: {}",
+                    &expr[ident_start..]
+                )));
+            };
+            let inner = &expr[cursor + 1..close_idx];
+            let replacement = self.resolve_runtime_helper(ctx, day, stock, ident, inner)?;
+            output.push_str(&replacement);
+            cursor = close_idx + 1;
+            let _ = whitespace_start;
+        }
+        Ok(output)
+    }
+
+    fn resolve_runtime_helper(
+        &self,
+        ctx: &StrategyContext<'_>,
+        day: &DayExpressionState,
+        stock: Option<&StockExpressionState>,
+        helper: &str,
+        args_src: &str,
+    ) -> Result<String, BacktestError> {
+        let args = Self::split_top_level_args(args_src);
+        match helper {
+            "factor" => {
+                let key = Self::parse_string_or_identifier(
+                    args.first().map(String::as_str).unwrap_or_default(),
+                )?;
+                Ok(format!("factors[{}]", Self::quote_rhai_string(&key)))
+            }
+            "day_factor" => {
+                let key = Self::parse_string_or_identifier(
+                    args.first().map(String::as_str).unwrap_or_default(),
+                )?;
+                Ok(format!("day_factors[{}]", Self::quote_rhai_string(&key)))
+            }
+            "rolling_mean" | "sma" => {
+                if args.len() != 2 {
+                    return Err(BacktestError::Execution(format!(
+                        "{helper} expects 2 arguments"
+                    )));
+                }
+                let field = Self::parse_string_or_identifier(&args[0])?;
+                let lookback = Self::parse_positive_usize(&args[1])?;
+                let value = self.resolve_rolling_mean(ctx, day, stock, &field, lookback)?;
+                Ok(format!("{value:.12}"))
+            }
+            other => Err(BacktestError::Execution(format!(
+                "unsupported platform helper: {other}"
+            ))),
+        }
+    }
+
+    fn resolve_rolling_mean(
+        &self,
+        ctx: &StrategyContext<'_>,
+        day: &DayExpressionState,
+        stock: Option<&StockExpressionState>,
+        field: &str,
+        lookback: usize,
+    ) -> Result<f64, BacktestError> {
+        if lookback == 0 {
+            return Err(BacktestError::Execution(
+                "rolling_mean lookback must be positive".to_string(),
+            ));
+        }
+        let value = match field {
+            "benchmark_close" => ctx.data.benchmark_moving_average(day.date, lookback),
+            "signal_close" => ctx
+                .data
+                .market_decision_close_moving_average(day.date, &self.config.signal_symbol, lookback),
+            "signal_volume" => ctx
+                .data
+                .market_decision_volume_moving_average(day.date, &self.config.signal_symbol, lookback),
+            other => {
+                let stock = stock.ok_or_else(|| {
+                    BacktestError::Execution(format!(
+                        "rolling_mean(\"{other}\", {lookback}) requires stock context"
+                    ))
+                })?;
+                ctx.data
+                    .market_decision_numeric_moving_average(day.date, &stock.symbol, other, lookback)
+            }
+        };
+        value.ok_or_else(|| {
+            BacktestError::Execution(format!(
+                "missing rolling mean for field {field} with lookback {lookback}"
+            ))
+        })
+    }
+
+    fn split_top_level_args(args: &str) -> Vec<String> {
+        let mut parts = Vec::new();
+        let mut start = 0usize;
+        let mut paren_depth = 0i32;
+        let mut brace_depth = 0i32;
+        let mut bracket_depth = 0i32;
+        let mut in_single_quote = false;
+        let mut in_double_quote = false;
+        let mut escaped = false;
+        for (idx, ch) in args.char_indices() {
+            if escaped {
+                escaped = false;
+                continue;
+            }
+            match ch {
+                '\\' if in_single_quote || in_double_quote => {
+                    escaped = true;
+                }
+                '\'' if !in_double_quote => {
+                    in_single_quote = !in_single_quote;
+                }
+                '"' if !in_single_quote => {
+                    in_double_quote = !in_double_quote;
+                }
+                _ if in_single_quote || in_double_quote => {}
+                '(' => paren_depth += 1,
+                ')' => paren_depth -= 1,
+                '{' => brace_depth += 1,
+                '}' => brace_depth -= 1,
+                '[' => bracket_depth += 1,
+                ']' => bracket_depth -= 1,
+                ',' if paren_depth == 0 && brace_depth == 0 && bracket_depth == 0 => {
+                    let part = args[start..idx].trim();
+                    if !part.is_empty() {
+                        parts.push(part.to_string());
+                    }
+                    start = idx + ch.len_utf8();
+                }
+                _ => {}
+            }
+        }
+        let tail = args[start..].trim();
+        if !tail.is_empty() {
+            parts.push(tail.to_string());
+        }
+        parts
+    }
+
+    fn parse_string_or_identifier(raw: &str) -> Result<String, BacktestError> {
+        let trimmed = raw.trim();
+        if trimmed.is_empty() {
+            return Err(BacktestError::Execution(
+                "platform helper argument cannot be empty".to_string(),
+            ));
+        }
+        if (trimmed.starts_with('"') && trimmed.ends_with('"'))
+            || (trimmed.starts_with('\'') && trimmed.ends_with('\''))
+        {
+            return Ok(trimmed[1..trimmed.len() - 1].to_string());
+        }
+        if Self::is_expression_identifier(trimmed) {
+            return Ok(trimmed.to_string());
+        }
+        Err(BacktestError::Execution(format!(
+            "platform helper expects a factor name or string literal, got {trimmed}"
+        )))
+    }
+
+    fn parse_positive_usize(raw: &str) -> Result<usize, BacktestError> {
+        let trimmed = raw.trim();
+        let value = trimmed.parse::<usize>().map_err(|_| {
+            BacktestError::Execution(format!(
+                "platform helper expects a positive integer lookback, got {trimmed}"
+            ))
+        })?;
+        if value == 0 {
+            return Err(BacktestError::Execution(
+                "platform helper lookback must be positive".to_string(),
+            ));
+        }
+        Ok(value)
+    }
+
+    fn quote_rhai_string(value: &str) -> String {
+        let escaped = value
+            .replace('\\', "\\\\")
+            .replace('"', "\\\"");
+        format!("\"{escaped}\"")
+    }
+
+    fn find_matching_paren(expr: &str, open_idx: usize) -> Option<usize> {
+        let mut paren_depth = 0i32;
+        let mut in_single_quote = false;
+        let mut in_double_quote = false;
+        let mut escaped = false;
+        for (idx, ch) in expr[open_idx..].char_indices() {
+            let absolute_idx = open_idx + idx;
+            if escaped {
+                escaped = false;
+                continue;
+            }
+            match ch {
+                '\\' if in_single_quote || in_double_quote => {
+                    escaped = true;
+                }
+                '\'' if !in_double_quote => {
+                    in_single_quote = !in_single_quote;
+                }
+                '"' if !in_single_quote => {
+                    in_double_quote = !in_double_quote;
+                }
+                _ if in_single_quote || in_double_quote => {}
+                '(' => paren_depth += 1,
+                ')' => {
+                    paren_depth -= 1;
+                    if paren_depth == 0 {
+                        return Some(absolute_idx);
+                    }
+                }
+                _ => {}
+            }
+        }
+        None
+    }
+
     fn declared_prelude_identifiers(prelude: &str) -> BTreeSet<String> {
         prelude
             .lines()
@@ -1206,12 +1477,13 @@ impl PlatformExprStrategy {
 
     fn eval_float(
         &self,
+        ctx: &StrategyContext<'_>,
         expr: &str,
         day: &DayExpressionState,
         stock: Option<&StockExpressionState>,
         position: Option<&PositionExpressionState>,
     ) -> Result<f64, BacktestError> {
-        let value = self.eval_dynamic(expr, day, stock, position)?;
+        let value = self.eval_dynamic(ctx, expr, day, stock, position)?;
         if let Some(number) = value.clone().try_cast::<f64>() {
             return Ok(number);
         }
@@ -1229,12 +1501,13 @@ impl PlatformExprStrategy {
 
     fn eval_bool(
         &self,
+        ctx: &StrategyContext<'_>,
         expr: &str,
         day: &DayExpressionState,
         stock: Option<&StockExpressionState>,
         position: Option<&PositionExpressionState>,
     ) -> Result<bool, BacktestError> {
-        let value = self.eval_dynamic(expr, day, stock, position)?;
+        let value = self.eval_dynamic(ctx, expr, day, stock, position)?;
         if let Some(boolean) = value.clone().try_cast::<bool>() {
             return Ok(boolean);
         }
@@ -1252,38 +1525,42 @@ impl PlatformExprStrategy {
 
     fn trading_ratio(
         &self,
+        ctx: &StrategyContext<'_>,
         day: &DayExpressionState,
     ) -> Result<f64, BacktestError> {
-        self.eval_float(&self.config.exposure_expr, day, None, None)
+        self.eval_float(ctx, &self.config.exposure_expr, day, None, None)
             .map(|value| value.clamp(0.0, 1.0))
     }
 
     fn market_cap_band(
         &self,
+        ctx: &StrategyContext<'_>,
         day: &DayExpressionState,
     ) -> Result<(f64, f64), BacktestError> {
-        let low = self.eval_float(&self.config.market_cap_lower_expr, day, None, None)?;
-        let high = self.eval_float(&self.config.market_cap_upper_expr, day, None, None)?;
+        let low = self.eval_float(ctx, &self.config.market_cap_lower_expr, day, None, None)?;
+        let high = self.eval_float(ctx, &self.config.market_cap_upper_expr, day, None, None)?;
         Ok((low.min(high), low.max(high)))
     }
 
     fn selection_limit(
         &self,
+        ctx: &StrategyContext<'_>,
         day: &DayExpressionState,
     ) -> Result<usize, BacktestError> {
-        let value = self.eval_float(&self.config.selection_limit_expr, day, None, None)?;
+        let value = self.eval_float(ctx, &self.config.selection_limit_expr, day, None, None)?;
         Ok(value.round().max(1.0) as usize)
     }
 
     fn stock_passes_expr(
         &self,
+        ctx: &StrategyContext<'_>,
         day: &DayExpressionState,
         stock: &StockExpressionState,
     ) -> Result<bool, BacktestError> {
         if self.config.stock_filter_expr.trim().is_empty() {
             return Ok(true);
         }
-        self.eval_bool(&self.config.stock_filter_expr, day, Some(stock), None)
+        self.eval_bool(ctx, &self.config.stock_filter_expr, day, Some(stock), None)
     }
 
     fn field_value(&self, row: &EligibleUniverseSnapshot) -> f64 {
@@ -1356,12 +1633,13 @@ impl PlatformExprStrategy {
 
     fn rank_value(
         &self,
+        ctx: &StrategyContext<'_>,
         day: &DayExpressionState,
         candidate: &EligibleUniverseSnapshot,
         stock: &StockExpressionState,
     ) -> Result<f64, BacktestError> {
         if !self.config.rank_expr.trim().is_empty() {
-            return self.eval_float(&self.config.rank_expr, day, Some(stock), None);
+            return self.eval_float(ctx, &self.config.rank_expr, day, Some(stock), None);
         }
         Ok(self
             .stock_numeric_field_value(candidate, stock, self.config.rank_by.as_str())
@@ -1448,7 +1726,7 @@ impl PlatformExprStrategy {
             if field_value < band_low || field_value > band_high {
                 continue;
             }
-            let rank_value = self.rank_value(day, &candidate, &stock)?;
+            let rank_value = self.rank_value(ctx, day, &candidate, &stock)?;
             candidates.push((candidate, stock, rank_value));
         }
         candidates.sort_by(|lhs, rhs| {
@@ -1478,7 +1756,7 @@ impl PlatformExprStrategy {
                 }
                 continue;
             }
-            if !self.stock_passes_expr(day, &stock)? {
+            if !self.stock_passes_expr(ctx, day, &stock)? {
                 if diagnostics.len() < 12 {
                     diagnostics.push(format!("{} rejected by stock_expr", candidate.symbol));
                 }
@@ -1520,7 +1798,7 @@ impl PlatformExprStrategy {
             quantity: position.quantity as i64,
             sellable_qty: position.sellable_qty(date) as i64,
         };
-        let stop_result = self.eval_dynamic(&self.config.stop_loss_expr, day, Some(&stock), Some(&position_state))?;
+        let stop_result = self.eval_dynamic(ctx, &self.config.stop_loss_expr, day, Some(&stock), Some(&position_state))?;
         let stop_hit = if let Some(boolean) = stop_result.clone().try_cast::<bool>() {
             boolean
         } else if let Some(multiplier) = stop_result.clone().try_cast::<f64>() {
@@ -1530,7 +1808,7 @@ impl PlatformExprStrategy {
         } else {
             false
         };
-        let take_result = self.eval_dynamic(&self.config.take_profit_expr, day, Some(&stock), Some(&position_state))?;
+        let take_result = self.eval_dynamic(ctx, &self.config.take_profit_expr, day, Some(&stock), Some(&position_state))?;
         let profit_hit = if let Some(boolean) = take_result.clone().try_cast::<bool>() {
             boolean
         } else if let Some(multiplier) = take_result.clone().try_cast::<f64>() {
@@ -1575,9 +1853,11 @@ impl Strategy for PlatformExprStrategy {
         }
 
         let day = self.day_state(ctx, date)?;
-        let trading_ratio = self.trading_ratio(&day)?;
-        let (band_low, band_high) = self.market_cap_band(&day)?;
-        let selection_limit = self.selection_limit(&day)?.min(self.config.max_positions.max(1));
+        let trading_ratio = self.trading_ratio(ctx, &day)?;
+        let (band_low, band_high) = self.market_cap_band(ctx, &day)?;
+        let selection_limit = self
+            .selection_limit(ctx, &day)?
+            .min(self.config.max_positions.max(1));
         let (stock_list, selection_notes) =
             self.select_symbols(ctx, date, &day, band_low, band_high, selection_limit)?;
         let periodic_rebalance = ctx.decision_index % self.config.refresh_rate == 0;
@@ -1630,7 +1910,7 @@ impl Strategy for PlatformExprStrategy {
                             if self.buy_rejection_reason(ctx, date, symbol, &stock)?.is_some() {
                                 continue;
                             }
-                            if !self.stock_passes_expr(&day, &stock)? {
+                            if !self.stock_passes_expr(ctx, &day, &stock)? {
                                 continue;
                             }
                             order_intents.push(OrderIntent::Value {
@@ -1694,7 +1974,7 @@ impl Strategy for PlatformExprStrategy {
                 if self.buy_rejection_reason(ctx, date, symbol, &stock)?.is_some() {
                     continue;
                 }
-                if !self.stock_passes_expr(&day, &stock)? {
+                if !self.stock_passes_expr(ctx, &day, &stock)? {
                     continue;
                 }
                 order_intents.push(OrderIntent::Value {