diff --git a/crates/fidc-core/src/broker.rs b/crates/fidc-core/src/broker.rs
index fca7803..e443483 100644
--- a/crates/fidc-core/src/broker.rs
+++ b/crates/fidc-core/src/broker.rs
@@ -10,6 +10,7 @@ use crate::events::{
     AccountEvent, FillEvent, OrderEvent, OrderSide, OrderStatus, PositionEvent, ProcessEvent,
     ProcessEventKind,
 };
+use crate::fixed_point::FixedMoney;
 use crate::instrument::Instrument;
 use crate::portfolio::PortfolioState;
 use crate::risk_control::{ChinaAShareRiskControl, FidcRiskControlConfig, RiskCheckScope};
@@ -2585,7 +2586,7 @@ where
             } else {
                 0.0
             };
-            if buy_cash_out <= projected_cash + 1e-6 {
+            if Self::fixed_cash_fits(buy_cash_out, projected_cash) {
                 if proportion_diff < best_proportion_diff - 1e-12
                     || ((proportion_diff - best_proportion_diff).abs() <= 1e-12
                         && safety_value > best_safety)
@@ -3150,9 +3151,14 @@ where
         if quantity == 0 {
             return 0.0;
         }
-        let gross = price * quantity as f64;
-        let cost = self.cost_model.calculate(date, OrderSide::Sell, gross);
-        gross - cost.total()
+        let gross = Self::fixed_gross_amount(price, quantity);
+        let cost = self
+            .cost_model
+            .calculate(date, OrderSide::Sell, gross.to_f64());
+        gross
+            .checked_sub(cost.fixed_total())
+            .expect("fixed-point sell proceeds underflow")
+            .to_f64()
     }
 
     fn sell_target_denial_reason(
@@ -3256,9 +3262,23 @@ where
         if quantity == 0 {
             return 0.0;
         }
-        let gross = price * quantity as f64;
-        let cost = self.cost_model.calculate(date, OrderSide::Buy, gross);
-        gross + cost.total()
+        let gross = Self::fixed_gross_amount(price, quantity);
+        let cost = self
+            .cost_model
+            .calculate(date, OrderSide::Buy, gross.to_f64());
+        gross
+            .checked_add(cost.fixed_total())
+            .expect("fixed-point buy cash overflow")
+            .to_f64()
+    }
+
+    fn fixed_gross_amount(price: f64, quantity: u32) -> FixedMoney {
+        FixedMoney::from_f64(price * quantity as f64)
+            .expect("execution gross amount must be finite fixed-point money")
+    }
+
+    fn fixed_cash_fits(value: f64, limit: f64) -> bool {
+        FixedMoney::f64_fits_within(value, limit).unwrap_or(false)
     }
 
     fn can_afford_minimum_buy(
@@ -3283,8 +3303,10 @@ where
         }
         let minimum_execution_price =
             self.snapshot_execution_price(snapshot, OrderSide::Buy, Some(minimum_buy_quantity));
-        self.estimated_buy_cash_out(date, minimum_execution_price, minimum_buy_quantity)
-            <= portfolio.cash() + 1e-6
+        Self::fixed_cash_fits(
+            self.estimated_buy_cash_out(date, minimum_execution_price, minimum_buy_quantity),
+            portfolio.cash(),
+        )
     }
 
     fn process_sell(
@@ -3722,7 +3744,8 @@ where
         }
         for leg in &execution_legs {
             let leg_cash_before = portfolio.cash();
-            let gross_amount = leg.price * leg.quantity as f64;
+            let gross_money = Self::fixed_gross_amount(leg.price, leg.quantity);
+            let gross_amount = gross_money.to_f64();
             let cost = self.cost_model.calculate_with_order_state(
                 date,
                 OrderSide::Sell,
@@ -3730,7 +3753,10 @@ where
                 Some(order_id),
                 commission_state,
             );
-            let net_cash = gross_amount - cost.total();
+            let net_cash = gross_money
+                .checked_sub(cost.fixed_total())
+                .expect("fixed-point sell proceeds underflow")
+                .to_f64();
             let realized_pnl = portfolio
                 .position_mut(symbol)
                 .sell_with_mark_price(leg.quantity, leg.price, leg.mark_price)
@@ -3738,7 +3764,9 @@ where
             if let Some(position) = portfolio.position_mut_if_exists(symbol) {
                 position.record_trade_cost(cost.total());
             }
-            portfolio.apply_cash_delta(net_cash);
+            portfolio
+                .apply_cash_delta(net_cash)
+                .map_err(BacktestError::Execution)?;
 
             report.fill_events.push(FillEvent {
                 date,
@@ -5371,7 +5399,8 @@ where
         }
         for leg in &execution_legs {
             let leg_cash_before = portfolio.cash();
-            let gross_amount = leg.price * leg.quantity as f64;
+            let gross_money = Self::fixed_gross_amount(leg.price, leg.quantity);
+            let gross_amount = gross_money.to_f64();
             let cost = self.cost_model.calculate_with_order_state(
                 date,
                 OrderSide::Buy,
@@ -5379,9 +5408,14 @@ where
                 Some(order_id),
                 commission_state,
             );
-            let cash_out = gross_amount + cost.total();
+            let cash_out = gross_money
+                .checked_add(cost.fixed_total())
+                .expect("fixed-point buy cash overflow")
+                .to_f64();
 
-            portfolio.apply_cash_delta(-cash_out);
+            portfolio
+                .apply_cash_delta(-cash_out)
+                .map_err(BacktestError::Execution)?;
             portfolio.position_mut(symbol).buy_with_mark_price(
                 date,
                 leg.quantity,
@@ -5766,7 +5800,10 @@ where
         let mut quantity =
             self.round_buy_quantity(raw_quantity, minimum_order_quantity, order_step_size);
         while quantity >= minimum {
-            if self.estimated_buy_cash_out(date, price, quantity) <= value_budget + 1e-6 {
+            if Self::fixed_cash_fits(
+                self.estimated_buy_cash_out(date, price, quantity),
+                value_budget,
+            ) {
                 return quantity;
             }
             quantity =
@@ -5820,7 +5857,10 @@ where
                 })
                 .filter(|price| price.is_finite() && *price > 0.0)
                 .unwrap_or(fallback_price);
-            if self.estimated_buy_cash_out(date, execution_price, quantity) <= value_budget + 1e-6 {
+            if Self::fixed_cash_fits(
+                self.estimated_buy_cash_out(date, execution_price, quantity),
+                value_budget,
+            ) {
                 return quantity;
             }
             quantity =
@@ -5857,7 +5897,7 @@ where
             self.round_buy_quantity(requested_qty, minimum_order_quantity, order_step_size);
         while quantity > 0 {
             let gross = price * quantity as f64;
-            if gross_limit.is_some_and(|limit| gross > limit + 1e-6) {
+            if gross_limit.is_some_and(|limit| !Self::fixed_cash_fits(gross, limit)) {
                 quantity = self.decrement_order_quantity(
                     quantity,
                     minimum_order_quantity,
@@ -5866,7 +5906,10 @@ where
                 continue;
             }
             let cost = self.cost_model.calculate(date, OrderSide::Buy, gross);
-            if gross + cost.total() <= cash + 1e-6 {
+            let cash_out = FixedMoney::checked_sum_f64([gross, cost.total()])
+                .expect("buy cash must be finite fixed-point money")
+                .to_f64();
+            if Self::fixed_cash_fits(cash_out, cash) {
                 return quantity;
             }
             quantity =
@@ -5886,7 +5929,9 @@ where
         if filled_qty >= requested_qty {
             return None;
         }
-        if gross_limit.is_some_and(|limit| price * requested_qty as f64 > limit + 1e-6) {
+        if gross_limit
+            .is_some_and(|limit| !Self::fixed_cash_fits(price * requested_qty as f64, limit))
+        {
             Some("value budget limit")
         } else if cash_limit.is_finite() {
             Some("insufficient cash after fees")
@@ -6326,7 +6371,9 @@ where
                         break;
                     }
                     let candidate_gross = gross_amount + quote_price * take_qty as f64;
-                    if gross_limit.is_some_and(|limit| candidate_gross > limit + 1e-6) {
+                    if gross_limit
+                        .is_some_and(|limit| !Self::fixed_cash_fits(candidate_gross, limit))
+                    {
                         budget_block_reason = Some("value budget limit");
                         take_qty = self.decrement_order_quantity(
                             take_qty,
@@ -6339,7 +6386,11 @@ where
                         .cost_model
                         .calculate(snapshot.date, OrderSide::Buy, candidate_gross)
                         .total();
-                    if candidate_gross + candidate_cost <= cash + 1e-6 {
+                    let candidate_cash =
+                        FixedMoney::checked_sum_f64([candidate_gross, candidate_cost])
+                            .expect("buy cash must be finite fixed-point money")
+                            .to_f64();
+                    if Self::fixed_cash_fits(candidate_cash, cash) {
                         break;
                     }
                     budget_block_reason = Some("insufficient cash after fees");
@@ -6586,6 +6637,7 @@ mod tests {
         IntradayExecutionQuote, PriceField,
     };
     use crate::events::{OrderSide, OrderStatus};
+    use crate::fixed_point::FixedMoney;
     use crate::instrument::Instrument;
     use crate::portfolio::PortfolioState;
     use crate::risk_control::FidcRiskControlConfig;
@@ -7650,7 +7702,7 @@ mod tests {
             1_000,
             10.0,
         );
-        portfolio.apply_cash_delta(-10_000.0);
+        portfolio.apply_cash_delta(-10_000.0).unwrap();
         let mut report = BrokerExecutionReport::default();
 
         broker
@@ -7708,7 +7760,7 @@ mod tests {
             10_000,
             10.0,
         );
-        portfolio.apply_cash_delta(-100_000.0);
+        portfolio.apply_cash_delta(-100_000.0).unwrap();
         let mut report = BrokerExecutionReport::default();
 
         broker
@@ -7766,7 +7818,7 @@ mod tests {
             1_000,
             10.0,
         );
-        portfolio.apply_cash_delta(-10_000.0);
+        portfolio.apply_cash_delta(-10_000.0).unwrap();
         let mut report = BrokerExecutionReport::default();
 
         broker
@@ -7856,7 +7908,7 @@ mod tests {
             1_000,
             10.0,
         );
-        portfolio.apply_cash_delta(-10_000.0);
+        portfolio.apply_cash_delta(-10_000.0).unwrap();
         let mut report = BrokerExecutionReport::default();
 
         broker
@@ -7943,7 +7995,7 @@ mod tests {
             10_000,
             10.0,
         );
-        portfolio.apply_cash_delta(-100_000.0);
+        portfolio.apply_cash_delta(-100_000.0).unwrap();
         let mut report = BrokerExecutionReport::default();
 
         broker
@@ -9122,7 +9174,7 @@ mod tests {
         .expect("valid dataset");
         let mut portfolio = PortfolioState::new(1_000_000.0);
         portfolio.position_mut(symbol).buy(prev_date, 72_600, 4.0);
-        portfolio.apply_cash_delta(-290_400.0);
+        portfolio.apply_cash_delta(-290_400.0).unwrap();
         let mut report = BrokerExecutionReport::default();
 
         broker
@@ -9166,13 +9218,10 @@ mod tests {
         let date = chrono::NaiveDate::from_ymd_opt(2023, 5, 8).expect("valid date");
         let symbol = "603101.SH";
         let broker = BrokerSimulator::new_with_execution_price(
-            ChinaAShareCostModel {
-                commission_rate: 0.0003,
-                stamp_tax_rate_before_change: 0.0005,
-                stamp_tax_rate_after_change: 0.0005,
-                minimum_commission: 5.0,
-                ..ChinaAShareCostModel::default()
-            },
+            ChinaAShareCostModel::default()
+                .with_commission_rate(0.0003)
+                .with_stamp_tax_rates(0.0005, 0.0005)
+                .with_minimum_commission(5.0),
             ChinaEquityRuleHooks,
             PriceField::Last,
         )
@@ -9515,7 +9564,20 @@ mod tests {
 
         let fill = report.fill_events.first().expect("fill event");
         assert_eq!(fill.quantity, 17_400);
-        assert!(fill.gross_amount + fill.commission <= value_budget + 1e-6);
+        let cash_out = FixedMoney::checked_sum_f64([
+            fill.gross_amount,
+            fill.commission,
+            fill.stamp_tax,
+            fill.transfer_fee,
+        ])
+        .unwrap()
+        .to_f64();
+        assert!(
+            BrokerSimulator::<ChinaAShareCostModel, ChinaEquityRuleHooks>::fixed_cash_fits(
+                cash_out,
+                value_budget
+            )
+        );
         assert!((fill.price - 7.15428).abs() < 1e-6);
     }
 
diff --git a/crates/fidc-core/src/cost.rs b/crates/fidc-core/src/cost.rs
index 7537692..61ad310 100644
--- a/crates/fidc-core/src/cost.rs
+++ b/crates/fidc-core/src/cost.rs
@@ -3,6 +3,7 @@ use std::collections::BTreeMap;
 use chrono::NaiveDate;
 
 use crate::events::OrderSide;
+use crate::fixed_point::{FixedChinaAShareCostModel, FixedMoney, FixedTradingCost};
 use crate::risk_control::TradingConstraintConfig;
 
 #[derive(Debug, Clone, Copy)]
@@ -14,7 +15,20 @@ pub struct TradingCost {
 
 impl TradingCost {
     pub fn total(self) -> f64 {
-        self.commission + self.stamp_tax + self.transfer_fee
+        self.fixed_total().to_f64()
+    }
+
+    pub fn fixed_total(self) -> FixedMoney {
+        FixedMoney::checked_sum_f64([self.commission, self.stamp_tax, self.transfer_fee])
+            .expect("trading costs must be finite fixed-point money")
+    }
+
+    fn from_fixed(value: FixedTradingCost) -> Self {
+        Self {
+            commission: value.commission.to_f64(),
+            stamp_tax: value.stamp_tax.to_f64(),
+            transfer_fee: value.transfer_fee.to_f64(),
+        }
     }
 }
 
@@ -35,12 +49,7 @@ pub trait CostModel {
 
 #[derive(Debug, Clone, Copy)]
 pub struct ChinaAShareCostModel {
-    pub commission_rate: f64,
-    pub stamp_tax_rate_before_change: f64,
-    pub stamp_tax_rate_after_change: f64,
-    pub stamp_tax_change_date: NaiveDate,
-    pub minimum_commission: f64,
-    pub transfer_fee_rate: f64,
+    fixed: FixedChinaAShareCostModel,
 }
 
 impl Default for ChinaAShareCostModel {
@@ -52,42 +61,93 @@ impl Default for ChinaAShareCostModel {
 impl ChinaAShareCostModel {
     pub fn from_trading_constraints(config: TradingConstraintConfig) -> Self {
         Self {
-            commission_rate: config.commission_rate,
-            stamp_tax_rate_before_change: config.stamp_tax_rate_before_change,
-            stamp_tax_rate_after_change: config.stamp_tax_rate_after_change,
-            stamp_tax_change_date: config.stamp_tax_change_date,
-            minimum_commission: config.minimum_commission,
-            transfer_fee_rate: config.transfer_fee_rate,
+            fixed: FixedChinaAShareCostModel {
+                commission_rate: Self::fixed_money(config.commission_rate, "commission rate"),
+                stamp_tax_rate_before_change: Self::fixed_money(
+                    config.stamp_tax_rate_before_change,
+                    "stamp tax rate before change",
+                ),
+                stamp_tax_rate_after_change: Self::fixed_money(
+                    config.stamp_tax_rate_after_change,
+                    "stamp tax rate after change",
+                ),
+                stamp_tax_change_date: config.stamp_tax_change_date,
+                minimum_commission: Self::fixed_money(
+                    config.minimum_commission,
+                    "minimum commission",
+                ),
+                transfer_fee_rate: Self::fixed_money(config.transfer_fee_rate, "transfer fee rate"),
+            },
         }
     }
 
+    pub fn set_commission_rate(&mut self, value: f64) {
+        self.fixed.commission_rate = Self::fixed_money(value, "commission rate");
+    }
+
+    pub fn set_minimum_commission(&mut self, value: f64) {
+        self.fixed.minimum_commission = Self::fixed_money(value, "minimum commission");
+    }
+
+    pub fn set_stamp_tax_rate_before_change(&mut self, value: f64) {
+        self.fixed.stamp_tax_rate_before_change =
+            Self::fixed_money(value, "stamp tax rate before change");
+    }
+
+    pub fn set_stamp_tax_rate_after_change(&mut self, value: f64) {
+        self.fixed.stamp_tax_rate_after_change =
+            Self::fixed_money(value, "stamp tax rate after change");
+    }
+
+    pub fn set_stamp_tax_change_date(&mut self, value: NaiveDate) {
+        self.fixed.stamp_tax_change_date = value;
+    }
+
+    pub fn with_commission_rate(mut self, value: f64) -> Self {
+        self.set_commission_rate(value);
+        self
+    }
+
+    pub fn with_minimum_commission(mut self, value: f64) -> Self {
+        self.set_minimum_commission(value);
+        self
+    }
+
+    pub fn with_stamp_tax_rates(mut self, before: f64, after: f64) -> Self {
+        self.set_stamp_tax_rate_before_change(before);
+        self.set_stamp_tax_rate_after_change(after);
+        self
+    }
+
     pub fn commission_for(&self, gross_amount: f64) -> f64 {
         if gross_amount <= 0.0 {
             return 0.0;
         }
-        (gross_amount * self.commission_rate).max(self.minimum_commission)
+        self.fixed_model()
+            .commission_for(Self::fixed_money(gross_amount, "gross amount"))
+            .to_f64()
     }
 
     pub fn stamp_tax_rate_for(&self, date: NaiveDate) -> f64 {
-        if date < self.stamp_tax_change_date {
-            self.stamp_tax_rate_before_change
-        } else {
-            self.stamp_tax_rate_after_change
-        }
+        self.fixed.stamp_tax_rate_for(date).to_f64()
     }
 
     pub fn stamp_tax_for(&self, date: NaiveDate, side: OrderSide, gross_amount: f64) -> f64 {
         if gross_amount <= 0.0 || side == OrderSide::Buy {
             return 0.0;
         }
-        gross_amount * self.stamp_tax_rate_for(date)
+        self.fixed_model()
+            .stamp_tax_for(date, side, Self::fixed_money(gross_amount, "gross amount"))
+            .to_f64()
     }
 
     pub fn transfer_fee_for(&self, gross_amount: f64) -> f64 {
         if gross_amount <= 0.0 {
             return 0.0;
         }
-        gross_amount * self.transfer_fee_rate
+        self.fixed_model()
+            .transfer_fee_for(Self::fixed_money(gross_amount, "gross amount"))
+            .to_f64()
     }
 
     pub fn commission_for_order_fill(
@@ -100,31 +160,29 @@ impl ChinaAShareCostModel {
             return 0.0;
         }
 
-        let raw_commission = gross_amount * self.commission_rate;
         let Some(order_id) = order_id else {
-            return raw_commission.max(self.minimum_commission);
+            return self.commission_for(gross_amount);
         };
 
         let remaining_minimum = commission_state
             .entry(order_id)
-            .or_insert(self.minimum_commission);
-        if raw_commission > *remaining_minimum {
-            let charged = if (*remaining_minimum - self.minimum_commission).abs() < 1e-12 {
-                raw_commission
-            } else {
-                raw_commission - *remaining_minimum
-            };
-            *remaining_minimum = 0.0;
-            charged
-        } else {
-            let charged = if (*remaining_minimum - self.minimum_commission).abs() < 1e-12 {
-                self.minimum_commission
-            } else {
-                0.0
-            };
-            *remaining_minimum -= raw_commission;
-            charged
-        }
+            .or_insert(self.fixed.minimum_commission.to_f64());
+        let mut fixed_remaining = Self::fixed_money(*remaining_minimum, "remaining commission");
+        let charged = self.fixed_model().commission_for_order_fill_remaining(
+            Self::fixed_money(gross_amount, "gross amount"),
+            &mut fixed_remaining,
+        );
+        *remaining_minimum = fixed_remaining.to_f64();
+        charged.to_f64()
+    }
+
+    fn fixed_money(value: f64, label: &str) -> FixedMoney {
+        FixedMoney::from_f64(value)
+            .unwrap_or_else(|| panic!("{label} is not representable as fixed-point money: {value}"))
+    }
+
+    fn fixed_model(&self) -> FixedChinaAShareCostModel {
+        self.fixed
     }
 }
 
@@ -138,15 +196,11 @@ impl CostModel for ChinaAShareCostModel {
             };
         }
 
-        let commission = self.commission_for(gross_amount);
-        let stamp_tax = self.stamp_tax_for(date, side, gross_amount);
-        let transfer_fee = self.transfer_fee_for(gross_amount);
-
-        TradingCost {
-            commission,
-            stamp_tax,
-            transfer_fee,
-        }
+        TradingCost::from_fixed(self.fixed_model().calculate(
+            date,
+            side,
+            Self::fixed_money(gross_amount, "gross amount"),
+        ))
     }
 
     fn calculate_with_order_state(
@@ -165,15 +219,25 @@ impl CostModel for ChinaAShareCostModel {
             };
         }
 
-        let commission = self.commission_for_order_fill(gross_amount, order_id, commission_state);
-        let stamp_tax = self.stamp_tax_for(date, side, gross_amount);
-        let transfer_fee = self.transfer_fee_for(gross_amount);
-
-        TradingCost {
+        let fixed_model = self.fixed_model();
+        let fixed_gross = Self::fixed_money(gross_amount, "gross amount");
+        let commission = if let Some(order_id) = order_id {
+            let remaining = commission_state
+                .entry(order_id)
+                .or_insert(self.fixed.minimum_commission.to_f64());
+            let mut fixed_remaining = Self::fixed_money(*remaining, "remaining commission");
+            let commission =
+                fixed_model.commission_for_order_fill_remaining(fixed_gross, &mut fixed_remaining);
+            *remaining = fixed_remaining.to_f64();
+            commission
+        } else {
+            fixed_model.commission_for(fixed_gross)
+        };
+        TradingCost::from_fixed(FixedTradingCost {
             commission,
-            stamp_tax,
-            transfer_fee,
-        }
+            stamp_tax: fixed_model.stamp_tax_for(date, side, fixed_gross),
+            transfer_fee: fixed_model.transfer_fee_for(fixed_gross),
+        })
     }
 }
 
@@ -182,13 +246,13 @@ mod tests {
     use super::*;
 
     #[test]
-    fn default_matches_configurable_trading_constraints() {
+    fn default_quantizes_fees_to_micro_yuan() {
         let model = ChinaAShareCostModel::default();
         let date = NaiveDate::from_ymd_opt(2025, 11, 11).expect("valid date");
 
-        assert!((model.commission_for(248_059.812) - 74.4179436).abs() < 1e-9);
+        assert!((model.commission_for(248_059.812) - 74.417944).abs() < 1e-12);
         assert!(
-            (model.stamp_tax_for(date, OrderSide::Sell, 245_747.007) - 122.8735035).abs() < 1e-9
+            (model.stamp_tax_for(date, OrderSide::Sell, 245_747.007) - 122.873504).abs() < 1e-12
         );
     }
 
diff --git a/crates/fidc-core/src/engine.rs b/crates/fidc-core/src/engine.rs
index a318cf1..fd30cfc 100644
--- a/crates/fidc-core/src/engine.rs
+++ b/crates/fidc-core/src/engine.rs
@@ -3217,7 +3217,9 @@ where
                 });
                 if outcome.cash_delta.abs() > f64::EPSILON {
                     let cash_before = portfolio.cash();
-                    portfolio.apply_cash_delta(outcome.cash_delta);
+                    portfolio
+                        .apply_cash_delta(outcome.cash_delta)
+                        .map_err(BacktestError::Execution)?;
                     report.account_events.push(AccountEvent {
                         date,
                         cash_before,
@@ -3279,7 +3281,9 @@ where
                     if reinvest_quantity > 0 {
                         let reinvest_cash = reinvest_quantity as f64 * price;
                         let residual_cash = receivable.amount - reinvest_cash;
-                        portfolio.apply_cash_delta(-reinvest_cash);
+                        portfolio
+                            .apply_cash_delta(-reinvest_cash)
+                            .map_err(BacktestError::Execution)?;
                         portfolio.position_mut(&receivable.symbol).buy(
                             date,
                             reinvest_quantity,
diff --git a/crates/fidc-core/src/fixed_point.rs b/crates/fidc-core/src/fixed_point.rs
index ccd2d79..ff309a0 100644
--- a/crates/fidc-core/src/fixed_point.rs
+++ b/crates/fidc-core/src/fixed_point.rs
@@ -1,10 +1,9 @@
-//! Independent fixed-point acceptance model for money and fee arithmetic.
+//! Fixed-point execution primitives for money and fee arithmetic.
 //!
-//! The execution kernel still exposes f64 because prices and source rows are
-//! represented that way today. This module is deliberately separate: it is a
-//! deterministic shadow model used to prove that cash, fees, budget checks,
-//! FIFO PnL, and external cash flows do not depend on binary floating-point
-//! accumulation.
+//! Market data and analytics remain floating point at their API boundaries.
+//! The execution kernel quantizes monetary values to micro-yuan before fee,
+//! budget and cash-ledger arithmetic so repeated fills and external cash flows
+//! do not accumulate binary floating-point drift.
 
 use std::collections::{BTreeMap, VecDeque};
 
@@ -105,6 +104,10 @@ impl FixedMoney {
         self.0.checked_mul(i128::from(quantity)).map(Self)
     }
 
+    pub fn checked_neg(self) -> Option<Self> {
+        self.0.checked_neg().map(Self)
+    }
+
     pub fn checked_mul_rate(self, rate: Self) -> Option<Self> {
         let product = self.0.checked_mul(rate.0)?;
         let half = MONEY_SCALE / 2;
@@ -116,6 +119,20 @@ impl FixedMoney {
         Some(Self(rounded))
     }
 
+    pub fn checked_sum_f64(values: impl IntoIterator<Item = f64>) -> Option<Self> {
+        values.into_iter().try_fold(Self::ZERO, |total, value| {
+            total.checked_add(Self::from_f64(value)?)
+        })
+    }
+
+    pub fn f64_fits_within(value: f64, limit: f64) -> Option<bool> {
+        let value = Self::from_f64(value)?;
+        if limit == f64::INFINITY {
+            return Some(true);
+        }
+        Some(value <= Self::from_f64(limit)?)
+    }
+
     pub fn abs(self) -> Self {
         Self(self.0.abs())
     }
@@ -217,6 +234,20 @@ impl FixedChinaAShareCostModel {
         let remaining = commission_state
             .entry(order_id)
             .or_insert(self.minimum_commission);
+        self.commission_for_order_fill_remaining(gross_amount, remaining)
+    }
+
+    pub fn commission_for_order_fill_remaining(
+        self,
+        gross_amount: FixedMoney,
+        remaining: &mut FixedMoney,
+    ) -> FixedMoney {
+        if gross_amount.raw() <= 0 {
+            return FixedMoney::ZERO;
+        }
+        let raw = gross_amount
+            .checked_mul_rate(self.commission_rate)
+            .expect("fixed commission multiplication overflow");
         if raw > *remaining {
             let charged = if *remaining == self.minimum_commission {
                 raw
@@ -415,7 +446,7 @@ mod tests {
     }
 
     #[test]
-    fn fixed_cost_matches_float_cost_model_within_one_micro_yuan() {
+    fn runtime_cost_model_matches_fixed_execution_primitive() {
         let fixed = fixed_model();
         let float = ChinaAShareCostModel::default();
         let dates = [
@@ -433,13 +464,7 @@ mod tests {
                         (actual.stamp_tax, expected.stamp_tax),
                         (actual.transfer_fee, expected.transfer_fee),
                     ] {
-                        assert!(
-                            (actual.to_f64() - expected).abs() <= 1.0 / MONEY_SCALE_F64,
-                            "fixed={} float={} gross={} date={date} side={side:?}",
-                            actual.to_f64(),
-                            expected,
-                            gross
-                        );
+                        assert_eq!(actual.to_f64(), expected);
                     }
                 }
             }
@@ -447,7 +472,7 @@ mod tests {
     }
 
     #[test]
-    fn fixed_order_commission_state_matches_float_order_split() {
+    fn runtime_split_commission_matches_fixed_execution_primitive() {
         let fixed = fixed_model();
         let float = ChinaAShareCostModel::default();
         let mut fixed_state = BTreeMap::new();
@@ -464,7 +489,7 @@ mod tests {
             fixed_total = fixed_total.checked_add(fixed_fee).unwrap();
             float_total += float_fee;
         }
-        assert!((fixed_total.to_f64() - float_total).abs() <= 4.0 / MONEY_SCALE_F64);
+        assert_eq!(fixed_total.to_f64(), float_total);
     }
 
     #[test]
@@ -493,6 +518,16 @@ mod tests {
         assert!(quantity < 5_000);
     }
 
+    #[test]
+    fn fixed_budget_comparison_rejects_one_micro_yuan_overrun() {
+        assert_eq!(FixedMoney::f64_fits_within(100.0, 100.0), Some(true));
+        assert_eq!(FixedMoney::f64_fits_within(100.000001, 100.0), Some(false));
+        assert_eq!(
+            FixedMoney::f64_fits_within(100.000001, f64::INFINITY),
+            Some(true)
+        );
+    }
+
     #[test]
     fn fixed_fifo_pnl_and_external_flow_are_deterministic() {
         let day_one = NaiveDate::from_ymd_opt(2025, 1, 2).unwrap();
diff --git a/crates/fidc-core/src/platform_expr_strategy.rs b/crates/fidc-core/src/platform_expr_strategy.rs
index 66e6019..6eef6f4 100644
--- a/crates/fidc-core/src/platform_expr_strategy.rs
+++ b/crates/fidc-core/src/platform_expr_strategy.rs
@@ -14,6 +14,7 @@ use crate::data::{
 };
 use crate::engine::BacktestError;
 use crate::events::OrderSide;
+use crate::fixed_point::FixedMoney;
 use crate::numeric_expr_vm::{
     self, EvalError as NumericVmEvalError, Program as NumericVmProgram,
     Scratch as NumericVmScratch, Value as NumericVmValue, ValueType as NumericVmValueType,
@@ -1904,14 +1905,47 @@ impl PlatformExprStrategy {
         (holding_days >= max_days).then_some(holding_days)
     }
 
-    fn buy_commission(&self, gross_amount: f64) -> f64 {
-        self.cost_model().commission_for(gross_amount)
+    fn buy_cost(&self, gross_amount: f64) -> f64 {
+        let model = self.cost_model();
+        FixedMoney::checked_sum_f64([
+            model.commission_for(gross_amount),
+            model.transfer_fee_for(gross_amount),
+        ])
+        .expect("projected buy costs must be finite fixed-point money")
+        .to_f64()
     }
 
     fn sell_cost(&self, date: NaiveDate, gross_amount: f64) -> f64 {
         let model = self.cost_model();
-        model.commission_for(gross_amount)
-            + model.stamp_tax_for(date, OrderSide::Sell, gross_amount)
+        FixedMoney::checked_sum_f64([
+            model.commission_for(gross_amount),
+            model.stamp_tax_for(date, OrderSide::Sell, gross_amount),
+            model.transfer_fee_for(gross_amount),
+        ])
+        .expect("projected sell costs must be finite fixed-point money")
+        .to_f64()
+    }
+
+    fn buy_cash_out(&self, gross_amount: f64) -> f64 {
+        FixedMoney::checked_sum_f64([gross_amount, self.buy_cost(gross_amount)])
+            .expect("projected buy cash must be finite fixed-point money")
+            .to_f64()
+    }
+
+    fn sell_net_cash(&self, date: NaiveDate, gross_amount: f64) -> f64 {
+        let gross = FixedMoney::from_f64(gross_amount)
+            .expect("projected sell gross must be finite fixed-point money");
+        gross
+            .checked_sub(
+                FixedMoney::from_f64(self.sell_cost(date, gross.to_f64()))
+                    .expect("projected sell costs must be finite fixed-point money"),
+            )
+            .expect("projected sell proceeds underflow")
+            .to_f64()
+    }
+
+    fn fixed_cash_fits(value: f64, limit: f64) -> bool {
+        FixedMoney::f64_fits_within(value, limit).unwrap_or(false)
     }
 
     fn cost_model(&self) -> ChinaAShareCostModel {
@@ -1919,19 +1953,19 @@ impl PlatformExprStrategy {
             self.config.risk_config.trading_constraints,
         );
         if let Some(value) = self.config.commission_rate {
-            model.commission_rate = value;
+            model.set_commission_rate(value);
         }
         if let Some(value) = self.config.minimum_commission {
-            model.minimum_commission = value;
+            model.set_minimum_commission(value);
         }
         if let Some(value) = self.config.stamp_tax_rate_before_change {
-            model.stamp_tax_rate_before_change = value;
+            model.set_stamp_tax_rate_before_change(value);
         }
         if let Some(value) = self.config.stamp_tax_rate_after_change {
-            model.stamp_tax_rate_after_change = value;
+            model.set_stamp_tax_rate_after_change(value);
         }
         if let Some(value) = self.config.stamp_tax_change_date {
-            model.stamp_tax_change_date = value;
+            model.set_stamp_tax_change_date(value);
         }
         model
     }
@@ -2026,7 +2060,7 @@ impl PlatformExprStrategy {
             self.round_lot_quantity(raw_quantity, minimum_order_quantity, order_step_size);
         while quantity >= minimum {
             let gross_amount = price * quantity as f64;
-            if gross_amount + self.buy_commission(gross_amount) <= value_budget + 1e-6 {
+            if Self::fixed_cash_fits(self.buy_cash_out(gross_amount), value_budget) {
                 return quantity;
             }
             quantity =
@@ -2609,7 +2643,9 @@ impl PlatformExprStrategy {
                         break;
                     }
                     let candidate_gross = gross_amount + quote_price * take_qty as f64;
-                    if gross_limit.is_some_and(|limit| candidate_gross > limit + 1e-6) {
+                    if gross_limit
+                        .is_some_and(|limit| !Self::fixed_cash_fits(candidate_gross, limit))
+                    {
                         take_qty = self.decrement_order_quantity(
                             take_qty,
                             minimum_order_quantity,
@@ -2617,7 +2653,7 @@ impl PlatformExprStrategy {
                         );
                         continue;
                     }
-                    if candidate_gross + self.buy_commission(candidate_gross) <= cash + 1e-6 {
+                    if Self::fixed_cash_fits(self.buy_cash_out(candidate_gross), cash) {
                         break;
                     }
                     take_qty = self.decrement_order_quantity(
@@ -2772,12 +2808,14 @@ impl PlatformExprStrategy {
                 }
             })?;
         let gross_amount = fill.price * fill.quantity as f64;
-        let sell_cost = self.sell_cost(date, gross_amount);
+        let net_cash = self.sell_net_cash(date, gross_amount);
         projected
             .position_mut(symbol)
             .sell(fill.quantity, fill.price)
             .ok()?;
-        projected.apply_cash_delta(gross_amount - sell_cost);
+        projected
+            .apply_cash_delta(net_cash)
+            .expect("projected sell cash must fit fixed-point ledger");
         *execution_state
             .intraday_turnover
             .entry(symbol.to_string())
@@ -2872,12 +2910,14 @@ impl PlatformExprStrategy {
             execution_state,
         )?;
         let gross_amount = fill.price * fill.quantity as f64;
-        let sell_cost = self.sell_cost(date, gross_amount);
+        let net_cash = self.sell_net_cash(date, gross_amount);
         projected
             .position_mut(symbol)
             .sell(fill.quantity, fill.price)
             .ok()?;
-        projected.apply_cash_delta(gross_amount - sell_cost);
+        projected
+            .apply_cash_delta(net_cash)
+            .expect("projected sell cash must fit fixed-point ledger");
         *execution_state
             .intraday_turnover
             .entry(symbol.to_string())
@@ -3339,8 +3379,8 @@ impl PlatformExprStrategy {
         };
         while quantity > 0 {
             let gross_amount = sizing_price * quantity as f64;
-            if gross_limit.map_or(true, |limit| gross_amount <= limit + 1e-6)
-                && gross_amount + self.buy_commission(gross_amount) <= cash_limit + 1e-6
+            if gross_limit.is_none_or(|limit| Self::fixed_cash_fits(gross_amount, limit))
+                && Self::fixed_cash_fits(self.buy_cash_out(gross_amount), cash_limit)
             {
                 break;
             }
@@ -3411,11 +3451,13 @@ impl PlatformExprStrategy {
             return ProjectedOrderValueResult::submitted_without_fill(submitted_quantity);
         };
         let gross_amount = fill.price * fill.quantity as f64;
-        let cash_out = gross_amount + self.buy_commission(gross_amount);
-        if cash_out > cash_limit + 1e-6 {
+        let cash_out = self.buy_cash_out(gross_amount);
+        if !Self::fixed_cash_fits(cash_out, cash_limit) {
             return ProjectedOrderValueResult::submitted_without_fill(submitted_quantity);
         }
-        projected.apply_cash_delta(-cash_out);
+        projected
+            .apply_cash_delta(-cash_out)
+            .expect("projected buy cash must fit fixed-point ledger");
         projected
             .position_mut(symbol)
             .buy(date, fill.quantity, fill.price);
@@ -13401,8 +13443,8 @@ mod tests {
         cfg.minimum_commission = Some(5.0);
         let strategy = PlatformExprStrategy::new(cfg);
 
-        assert!((strategy.buy_commission(100_000.0) - 30.0).abs() < 1e-9);
-        assert!((strategy.buy_commission(1_000.0) - 5.0).abs() < 1e-9);
+        assert!((strategy.buy_cost(100_000.0) - 30.0).abs() < 1e-9);
+        assert!((strategy.buy_cost(1_000.0) - 5.0).abs() < 1e-9);
     }
 
     #[test]
@@ -13412,7 +13454,7 @@ mod tests {
         cfg.minimum_commission = Some(0.0);
         let strategy = PlatformExprStrategy::new(cfg);
 
-        assert!((strategy.buy_commission(1_000.0) - 0.3).abs() < 1e-9);
+        assert!((strategy.buy_cost(1_000.0) - 0.3).abs() < 1e-9);
     }
 
     #[test]
@@ -18211,7 +18253,7 @@ mod tests {
         portfolio
             .position_mut(symbol)
             .buy(d(2023, 5, 4), 30_000, 10.0);
-        portfolio.apply_cash_delta(-300_000.0);
+        portfolio.apply_cash_delta(-300_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -18324,7 +18366,7 @@ mod tests {
         portfolio
             .position_mut(symbol)
             .buy(d(2023, 5, 4), 30_000, 10.0);
-        portfolio.apply_cash_delta(-300_000.0);
+        portfolio.apply_cash_delta(-300_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -18455,7 +18497,7 @@ mod tests {
         portfolio
             .position_mut(symbol)
             .buy(d(2023, 5, 4), 30_000, 10.0);
-        portfolio.apply_cash_delta(-300_000.0);
+        portfolio.apply_cash_delta(-300_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -18582,7 +18624,7 @@ mod tests {
         portfolio
             .position_mut(symbol)
             .buy(d(2023, 5, 4), 30_000, 10.0);
-        portfolio.apply_cash_delta(-300_000.0);
+        portfolio.apply_cash_delta(-300_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date,
@@ -18736,7 +18778,7 @@ mod tests {
         portfolio
             .position_mut("000002.SZ")
             .buy(prev_date, 2_400, 10.0);
-        portfolio.apply_cash_delta(-54_000.0);
+        portfolio.apply_cash_delta(-54_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -18897,7 +18939,7 @@ mod tests {
         .expect("dataset");
         let mut portfolio = PortfolioState::new(100_000.0);
         portfolio.position_mut(symbol).buy(prev_date, 3_000, 10.0);
-        portfolio.apply_cash_delta(-30_000.0);
+        portfolio.apply_cash_delta(-30_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -19053,7 +19095,7 @@ mod tests {
         .expect("dataset");
         let mut portfolio = PortfolioState::new(100_000.0);
         portfolio.position_mut(symbol).buy(prev_date, 3_000, 10.0);
-        portfolio.apply_cash_delta(-30_000.0);
+        portfolio.apply_cash_delta(-30_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -19209,7 +19251,7 @@ mod tests {
         .expect("dataset");
         let mut portfolio = PortfolioState::new(100_000.0);
         portfolio.position_mut(symbol).buy(prev_date, 3_000, 10.0);
-        portfolio.apply_cash_delta(-30_000.0);
+        portfolio.apply_cash_delta(-30_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
@@ -19370,7 +19412,7 @@ mod tests {
         portfolio
             .position_mut("000002.SZ")
             .buy(prev_date, 2_400, 10.0);
-        portfolio.apply_cash_delta(-54_000.0);
+        portfolio.apply_cash_delta(-54_000.0).unwrap();
         let subscriptions = BTreeSet::new();
         let ctx = StrategyContext {
             execution_date: date,
diff --git a/crates/fidc-core/src/portfolio.rs b/crates/fidc-core/src/portfolio.rs
index e867b99..db00ff7 100644
--- a/crates/fidc-core/src/portfolio.rs
+++ b/crates/fidc-core/src/portfolio.rs
@@ -4,6 +4,7 @@ use serde::{Deserialize, Serialize};
 use std::collections::{BTreeMap, BTreeSet};
 
 use crate::data::{DataSet, DataSetError, PriceField};
+use crate::fixed_point::{FixedMoney, MONEY_SCALE};
 
 #[derive(Debug, Clone)]
 pub struct PositionLot {
@@ -429,17 +430,17 @@ fn normalized_mark_price(mark_price: f64, fallback: f64) -> f64 {
 
 #[derive(Debug, Clone)]
 pub struct PortfolioState {
-    initial_cash: f64,
-    units: f64,
-    cash: f64,
+    initial_cash: FixedMoney,
+    units: FixedMoney,
+    cash: FixedMoney,
     /// Cumulative external cash flow (deposits positive, withdrawals negative).
     /// Trading proceeds, dividends, fees and financing are deliberately not
     /// included.  The value is used by the engine to build a cash-flow-neutral
     /// equity curve and is not a return measure itself.
-    external_cash_flow_total: f64,
-    cash_liabilities: f64,
+    external_cash_flow_total: FixedMoney,
+    cash_liabilities: FixedMoney,
     management_fee_rate: f64,
-    management_fees: f64,
+    management_fees: FixedMoney,
     positions: IndexMap<String, Position>,
     cash_receivables: Vec<CashReceivable>,
     pending_cash_flows: Vec<PendingCashFlow>,
@@ -466,14 +467,16 @@ pub(crate) struct SuccessorConversionOutcome {
 
 impl PortfolioState {
     pub fn new(initial_cash: f64) -> Self {
+        let initial_cash = Self::fixed_money(initial_cash, "initial cash")
+            .expect("initial cash must be finite fixed-point money");
         Self {
             initial_cash,
             units: initial_cash,
             cash: initial_cash,
-            external_cash_flow_total: 0.0,
-            cash_liabilities: 0.0,
+            external_cash_flow_total: FixedMoney::ZERO,
+            cash_liabilities: FixedMoney::ZERO,
             management_fee_rate: 0.0,
-            management_fees: 0.0,
+            management_fees: FixedMoney::ZERO,
             positions: IndexMap::new(),
             cash_receivables: Vec::new(),
             pending_cash_flows: Vec::new(),
@@ -484,27 +487,27 @@ impl PortfolioState {
     pub fn starting_cash(&self) -> f64 {
         // Keep the configured opening capital stable. External flows change
         // `units`, not the meaning of this reporting field.
-        self.initial_cash
+        self.initial_cash.to_f64()
     }
 
     pub fn initial_cash(&self) -> f64 {
-        self.initial_cash
+        self.initial_cash.to_f64()
     }
 
     pub fn units(&self) -> f64 {
-        self.units
+        self.units.to_f64()
     }
 
     pub fn cash(&self) -> f64 {
-        self.cash
+        self.cash.to_f64()
     }
 
     pub fn external_cash_flow_total(&self) -> f64 {
-        self.external_cash_flow_total
+        self.external_cash_flow_total.to_f64()
     }
 
     pub fn cash_liabilities(&self) -> f64 {
-        self.cash_liabilities
+        self.cash_liabilities.to_f64()
     }
 
     pub fn management_fee_rate(&self) -> f64 {
@@ -512,7 +515,7 @@ impl PortfolioState {
     }
 
     pub fn management_fees(&self) -> f64 {
-        self.management_fees
+        self.management_fees.to_f64()
     }
 
     pub fn positions(&self) -> &IndexMap<String, Position> {
@@ -533,8 +536,12 @@ impl PortfolioState {
             .or_insert_with(|| Position::new(symbol))
     }
 
-    pub fn apply_cash_delta(&mut self, delta: f64) {
-        self.cash += delta;
+    pub fn apply_cash_delta(&mut self, delta: f64) -> Result<(), String> {
+        self.cash = self
+            .cash
+            .checked_add(Self::fixed_money(delta, "cash delta")?)
+            .ok_or_else(|| "fixed-point cash overflow".to_string())?;
+        Ok(())
     }
 
     pub fn prune_flat_positions(&mut self) {
@@ -558,21 +565,34 @@ impl PortfolioState {
     }
 
     pub fn deposit_withdraw(&mut self, amount: f64) -> Result<(), String> {
-        if !amount.is_finite() {
-            return Err("deposit_withdraw amount must be finite".to_string());
-        }
-        if amount < 0.0 && self.cash - self.pending_withdrawal_total() + amount < -1e-6 {
-            let available_cash = self.cash - self.pending_withdrawal_total();
+        let amount_money = Self::fixed_money(amount, "deposit_withdraw amount")?;
+        let pending_withdrawal =
+            Self::fixed_money(self.pending_withdrawal_total(), "pending withdrawal total")?;
+        let available_cash = self
+            .cash
+            .checked_sub(pending_withdrawal)
+            .ok_or_else(|| "fixed-point available cash overflow".to_string())?;
+        let cash_after = available_cash
+            .checked_add(amount_money)
+            .ok_or_else(|| "fixed-point deposit_withdraw overflow".to_string())?;
+        if amount_money.raw() < 0 && cash_after.raw() < 0 {
             return Err(format!(
                 "insufficient cash for withdrawal amount={:.2} available_cash={:.2}",
-                amount, available_cash
+                amount,
+                available_cash.to_f64()
             ));
         }
 
         let unit_net_value = self.unit_net_value();
-        self.cash += amount;
-        self.external_cash_flow_total += amount;
-        self.rebase_units_after_external_cash_flow(unit_net_value);
+        self.cash = self
+            .cash
+            .checked_add(amount_money)
+            .ok_or_else(|| "fixed-point cash overflow".to_string())?;
+        self.external_cash_flow_total = self
+            .external_cash_flow_total
+            .checked_add(amount_money)
+            .ok_or_else(|| "fixed-point external cash flow overflow".to_string())?;
+        self.rebase_units_after_external_cash_flow(unit_net_value)?;
         Ok(())
     }
 
@@ -582,14 +602,21 @@ impl PortfolioState {
         amount: f64,
         reason: impl Into<String>,
     ) -> Result<(), String> {
-        if !amount.is_finite() {
-            return Err("deposit_withdraw amount must be finite".to_string());
-        }
-        if amount < 0.0 && self.cash - self.pending_withdrawal_total() + amount < -1e-6 {
-            let available_cash = self.cash - self.pending_withdrawal_total();
+        let amount_money = Self::fixed_money(amount, "deposit_withdraw amount")?;
+        let pending_withdrawal =
+            Self::fixed_money(self.pending_withdrawal_total(), "pending withdrawal total")?;
+        let available_cash = self
+            .cash
+            .checked_sub(pending_withdrawal)
+            .ok_or_else(|| "fixed-point available cash overflow".to_string())?;
+        let cash_after = available_cash
+            .checked_add(amount_money)
+            .ok_or_else(|| "fixed-point scheduled cash flow overflow".to_string())?;
+        if amount_money.raw() < 0 && cash_after.raw() < 0 {
             return Err(format!(
                 "insufficient cash for scheduled withdrawal amount={:.2} available_cash={:.2}",
-                amount, available_cash
+                amount,
+                available_cash.to_f64()
             ));
         }
         self.pending_cash_flows.push(PendingCashFlow {
@@ -620,24 +647,33 @@ impl PortfolioState {
         // negative after trades on an earlier day.  Validate the complete due
         // batch before mutating either cash or the pending queue so a failed
         // settlement is atomic and can be diagnosed/retried safely.
-        let incoming = due
-            .iter()
-            .filter(|flow| flow.amount > 0.0)
-            .map(|flow| flow.amount)
-            .sum::<f64>();
-        let outgoing = due
-            .iter()
-            .filter(|flow| flow.amount < 0.0)
-            .map(|flow| flow.amount)
-            .sum::<f64>();
-        if self.cash + incoming + outgoing < -1e-6 {
+        let incoming = Self::sum_fixed_money(
+            due.iter()
+                .filter(|flow| flow.amount > 0.0)
+                .map(|flow| flow.amount),
+            "incoming scheduled cash flows",
+        )?;
+        let outgoing = Self::sum_fixed_money(
+            due.iter()
+                .filter(|flow| flow.amount < 0.0)
+                .map(|flow| flow.amount),
+            "outgoing scheduled cash flows",
+        )?;
+        let net_due = incoming
+            .checked_add(outgoing)
+            .ok_or_else(|| "fixed-point scheduled cash flow overflow".to_string())?;
+        let cash_after = self
+            .cash
+            .checked_add(net_due)
+            .ok_or_else(|| "fixed-point cash settlement overflow".to_string())?;
+        if cash_after.raw() < 0 {
             self.pending_cash_flows = due.into_iter().chain(pending).collect();
             self.pending_cash_flows
                 .sort_by_key(|flow| flow.payable_date);
             return Err(format!(
                 "insufficient cash to settle delayed cash flows on {date}: cash={:.2} net_due={:.2}",
-                self.cash,
-                incoming + outgoing
+                self.cash.to_f64(),
+                net_due.to_f64()
             ));
         }
 
@@ -649,9 +685,16 @@ impl PortfolioState {
         let mut settled = Vec::with_capacity(due.len());
         for flow in due {
             let unit_net_value = self.unit_net_value();
-            self.cash += flow.amount;
-            self.external_cash_flow_total += flow.amount;
-            self.rebase_units_after_external_cash_flow(unit_net_value);
+            let amount = Self::fixed_money(flow.amount, "scheduled cash flow")?;
+            self.cash = self
+                .cash
+                .checked_add(amount)
+                .ok_or_else(|| "fixed-point cash overflow".to_string())?;
+            self.external_cash_flow_total = self
+                .external_cash_flow_total
+                .checked_add(amount)
+                .ok_or_else(|| "fixed-point external cash flow overflow".to_string())?;
+            self.rebase_units_after_external_cash_flow(unit_net_value)?;
             settled.push(flow);
         }
         self.pending_cash_flows = pending;
@@ -671,24 +714,38 @@ impl PortfolioState {
     }
 
     pub fn finance_repay(&mut self, amount: f64) -> Result<(), String> {
-        if !amount.is_finite() {
-            return Err("finance_repay amount must be finite".to_string());
-        }
-        if amount > 0.0 {
-            self.cash_liabilities += amount;
-            self.cash += amount;
+        let amount_money = Self::fixed_money(amount, "finance_repay amount")?;
+        if amount_money.raw() > 0 {
+            self.cash_liabilities = self
+                .cash_liabilities
+                .checked_add(amount_money)
+                .ok_or_else(|| "fixed-point cash liability overflow".to_string())?;
+            self.cash = self
+                .cash
+                .checked_add(amount_money)
+                .ok_or_else(|| "fixed-point cash overflow".to_string())?;
             return Ok(());
         }
-        if amount < 0.0 {
-            let repay_amount = (-amount).min(self.cash_liabilities);
-            if repay_amount > self.cash + 1e-6 {
+        if amount_money.raw() < 0 {
+            let requested = amount_money
+                .checked_neg()
+                .ok_or_else(|| "fixed-point finance repayment overflow".to_string())?;
+            let repay_amount = requested.min(self.cash_liabilities);
+            if repay_amount > self.cash {
                 return Err(format!(
                     "insufficient cash for finance repay amount={:.2} cash={:.2}",
-                    repay_amount, self.cash
+                    repay_amount.to_f64(),
+                    self.cash.to_f64()
                 ));
             }
-            self.cash_liabilities -= repay_amount;
-            self.cash -= repay_amount;
+            self.cash_liabilities = self
+                .cash_liabilities
+                .checked_sub(repay_amount)
+                .ok_or_else(|| "fixed-point cash liability underflow".to_string())?;
+            self.cash = self
+                .cash
+                .checked_sub(repay_amount)
+                .ok_or_else(|| "fixed-point cash underflow".to_string())?;
         }
         Ok(())
     }
@@ -706,11 +763,18 @@ impl PortfolioState {
     }
 
     pub fn apply_management_fee(&mut self, fee: f64) -> Result<(), String> {
-        if !fee.is_finite() || fee < 0.0 {
+        let fee_money = Self::fixed_money(fee, "management fee")?;
+        if fee_money.raw() < 0 {
             return Err("management fee must be finite and non-negative".to_string());
         }
-        self.cash -= fee;
-        self.management_fees += fee;
+        self.cash = self
+            .cash
+            .checked_sub(fee_money)
+            .ok_or_else(|| "fixed-point cash underflow".to_string())?;
+        self.management_fees = self
+            .management_fees
+            .checked_add(fee_money)
+            .ok_or_else(|| "fixed-point management fee overflow".to_string())?;
         Ok(())
     }
 
@@ -719,7 +783,12 @@ impl PortfolioState {
         let mut pending = Vec::new();
         for receivable in self.cash_receivables.drain(..) {
             if receivable.payable_date <= date {
-                self.cash += receivable.amount;
+                let amount = Self::fixed_money(receivable.amount, "cash receivable")
+                    .expect("cash receivable must be finite fixed-point money");
+                self.cash = self
+                    .cash
+                    .checked_add(amount)
+                    .expect("fixed-point cash overflow while settling receivable");
                 settled.push(receivable);
             } else {
                 pending.push(receivable);
@@ -838,7 +907,7 @@ impl PortfolioState {
     }
 
     pub fn total_equity(&self) -> f64 {
-        self.cash + self.market_value() - self.cash_liabilities
+        self.total_equity_money().to_f64()
     }
 
     pub fn total_value(&self) -> f64 {
@@ -850,18 +919,18 @@ impl PortfolioState {
     }
 
     pub fn unit_net_value(&self) -> f64 {
-        if self.units.abs() < f64::EPSILON {
+        if self.units.raw() == 0 {
             0.0
         } else {
-            self.total_equity() / self.units
+            self.total_equity() / self.units.to_f64()
         }
     }
 
     pub fn static_unit_net_value(&self) -> f64 {
-        if self.units.abs() < f64::EPSILON {
+        if self.units.raw() == 0 {
             0.0
         } else {
-            (self.total_equity() - self.daily_pnl()) / self.units
+            (self.total_equity() - self.daily_pnl()) / self.units.to_f64()
         }
     }
 
@@ -1025,6 +1094,43 @@ impl PortfolioState {
         })
     }
 
+    fn fixed_money(value: f64, label: &str) -> Result<FixedMoney, String> {
+        FixedMoney::from_f64(value)
+            .ok_or_else(|| format!("{label} is not representable as fixed-point money: {value}"))
+    }
+
+    fn sum_fixed_money(
+        values: impl IntoIterator<Item = f64>,
+        label: &str,
+    ) -> Result<FixedMoney, String> {
+        values
+            .into_iter()
+            .try_fold(FixedMoney::ZERO, |total, value| {
+                total
+                    .checked_add(Self::fixed_money(value, label)?)
+                    .ok_or_else(|| format!("fixed-point {label} overflow"))
+            })
+    }
+
+    fn market_value_money(&self) -> FixedMoney {
+        self.positions
+            .values()
+            .fold(FixedMoney::ZERO, |total, position| {
+                let value = Self::fixed_money(position.market_value(), "position market value")
+                    .expect("position market value must be finite fixed-point money");
+                total
+                    .checked_add(value)
+                    .expect("fixed-point market value overflow")
+            })
+    }
+
+    fn total_equity_money(&self) -> FixedMoney {
+        self.cash
+            .checked_add(self.market_value_money())
+            .and_then(|value| value.checked_sub(self.cash_liabilities))
+            .expect("fixed-point total equity overflow")
+    }
+
     fn refresh_dividend_receivables(&mut self) {
         let mut per_symbol = BTreeMap::<String, f64>::new();
         for receivable in &self.cash_receivables {
@@ -1035,10 +1141,21 @@ impl PortfolioState {
         }
     }
 
-    fn rebase_units_after_external_cash_flow(&mut self, unit_net_value_before: f64) {
+    fn rebase_units_after_external_cash_flow(
+        &mut self,
+        unit_net_value_before: f64,
+    ) -> Result<(), String> {
         if unit_net_value_before > 0.0 && unit_net_value_before.is_finite() {
-            self.units = self.total_equity() / unit_net_value_before;
+            let unit_nav = Self::fixed_money(unit_net_value_before, "unit net value")?;
+            let units_raw = self
+                .total_equity_money()
+                .raw()
+                .checked_mul(MONEY_SCALE)
+                .and_then(|value| value.checked_div(unit_nav.raw()))
+                .ok_or_else(|| "fixed-point unit rebase overflow".to_string())?;
+            self.units = FixedMoney::from_raw(units_raw);
         }
+        Ok(())
     }
 }
 
@@ -1052,6 +1169,22 @@ mod tests {
     };
     use std::collections::BTreeMap;
 
+    #[test]
+    fn cash_ledger_accumulates_micro_yuan_exactly() {
+        let mut portfolio = PortfolioState::new(1_000_000.0);
+        for _ in 0..100_000 {
+            portfolio.apply_cash_delta(-0.000001).unwrap();
+        }
+        assert_eq!(portfolio.cash, FixedMoney::from_raw(999_999_900_000));
+        assert_eq!(portfolio.cash(), 999_999.9);
+
+        for _ in 0..100_000 {
+            portfolio.apply_cash_delta(0.000001).unwrap();
+        }
+        assert_eq!(portfolio.cash, FixedMoney::from_raw(1_000_000_000_000));
+        assert_eq!(portfolio.cash(), 1_000_000.0);
+    }
+
     #[test]
     fn positions_preserve_insertion_order() {
         let date = NaiveDate::from_ymd_opt(2025, 1, 2).unwrap();
@@ -1682,7 +1815,7 @@ mod tests {
         // A strategy cannot spend the reserved cash by scheduling a second
         // withdrawal; settlement remains safe even if earlier trading reduced
         // the current cash balance.
-        portfolio.apply_cash_delta(-3_000.0);
+        portfolio.apply_cash_delta(-3_000.0).unwrap();
         let error = portfolio
             .settle_pending_cash_flows(date)
             .expect_err("settlement must reject an underfunded withdrawal batch");
diff --git a/crates/fidc-core/src/strategy.rs b/crates/fidc-core/src/strategy.rs
index ae198b2..8c8aed1 100644
--- a/crates/fidc-core/src/strategy.rs
+++ b/crates/fidc-core/src/strategy.rs
@@ -10,6 +10,7 @@ use crate::data::{
 };
 use crate::engine::BacktestError;
 use crate::events::{FillEvent, OrderEvent, OrderSide, OrderStatus, ProcessEvent};
+use crate::fixed_point::FixedMoney;
 use crate::futures::{FuturesAccountState, FuturesOrderIntent};
 use crate::instrument::Instrument;
 use crate::portfolio::PortfolioState;
@@ -1750,14 +1751,47 @@ impl OmniMicroCapStrategy {
         ChinaAShareCostModel::from_trading_constraints(self.config.risk_config.trading_constraints)
     }
 
-    fn buy_commission(&self, gross_amount: f64) -> f64 {
-        self.cost_model().commission_for(gross_amount)
+    fn buy_cost(&self, gross_amount: f64) -> f64 {
+        let model = self.cost_model();
+        FixedMoney::checked_sum_f64([
+            model.commission_for(gross_amount),
+            model.transfer_fee_for(gross_amount),
+        ])
+        .expect("projected buy costs must be finite fixed-point money")
+        .to_f64()
     }
 
     fn sell_cost(&self, date: NaiveDate, gross_amount: f64) -> f64 {
         let model = self.cost_model();
-        model.commission_for(gross_amount)
-            + model.stamp_tax_for(date, OrderSide::Sell, gross_amount)
+        FixedMoney::checked_sum_f64([
+            model.commission_for(gross_amount),
+            model.stamp_tax_for(date, OrderSide::Sell, gross_amount),
+            model.transfer_fee_for(gross_amount),
+        ])
+        .expect("projected sell costs must be finite fixed-point money")
+        .to_f64()
+    }
+
+    fn buy_cash_out(&self, gross_amount: f64) -> f64 {
+        FixedMoney::checked_sum_f64([gross_amount, self.buy_cost(gross_amount)])
+            .expect("projected buy cash must be finite fixed-point money")
+            .to_f64()
+    }
+
+    fn sell_net_cash(&self, date: NaiveDate, gross_amount: f64) -> f64 {
+        let gross = FixedMoney::from_f64(gross_amount)
+            .expect("projected sell gross must be finite fixed-point money");
+        gross
+            .checked_sub(
+                FixedMoney::from_f64(self.sell_cost(date, gross.to_f64()))
+                    .expect("projected sell costs must be finite fixed-point money"),
+            )
+            .expect("projected sell proceeds underflow")
+            .to_f64()
+    }
+
+    fn fixed_cash_fits(value: f64, limit: f64) -> bool {
+        FixedMoney::f64_fits_within(value, limit).unwrap_or(false)
     }
 
     fn round_lot_quantity(
@@ -1826,7 +1860,7 @@ impl OmniMicroCapStrategy {
         let mut quantity = self.round_lot_quantity((cash / sizing_price).floor() as u32, 100, 100);
         while quantity > 0 {
             let gross_amount = execution_price * quantity as f64;
-            if gross_amount + self.buy_commission(gross_amount) <= cash + 1e-6 {
+            if Self::fixed_cash_fits(self.buy_cash_out(gross_amount), cash) {
                 return quantity;
             }
             quantity = self.decrement_order_quantity(quantity, 100, 100);
@@ -1874,8 +1908,10 @@ impl OmniMicroCapStrategy {
         );
         while snapshot_requested_qty > 0 {
             let gross_amount = sizing_price * snapshot_requested_qty as f64;
-            let cash_out = gross_amount + self.buy_commission(gross_amount);
-            if cash_out <= order_value + 1e-6 && cash_out <= projected.cash() + 1e-6 {
+            let cash_out = self.buy_cash_out(gross_amount);
+            if Self::fixed_cash_fits(cash_out, order_value)
+                && Self::fixed_cash_fits(cash_out, projected.cash())
+            {
                 break;
             }
             snapshot_requested_qty = self.decrement_order_quantity(
@@ -1902,8 +1938,10 @@ impl OmniMicroCapStrategy {
         let mut quantity = snapshot_requested_qty;
         while quantity > 0 {
             let gross_amount = projected_execution_price * quantity as f64;
-            let cash_out = gross_amount + self.buy_commission(gross_amount);
-            if cash_out <= order_value + 1e-6 && cash_out <= projected.cash() + 1e-6 {
+            let cash_out = self.buy_cash_out(gross_amount);
+            if Self::fixed_cash_fits(cash_out, order_value)
+                && Self::fixed_cash_fits(cash_out, projected.cash())
+            {
                 break;
             }
             quantity =
@@ -1918,8 +1956,10 @@ impl OmniMicroCapStrategy {
             .unwrap_or(projected_execution_price);
         while quantity > 0 {
             let gross_amount = execution_price * quantity as f64;
-            let cash_out = gross_amount + self.buy_commission(gross_amount);
-            if cash_out <= order_value + 1e-6 && cash_out <= projected.cash() + 1e-6 {
+            let cash_out = self.buy_cash_out(gross_amount);
+            if Self::fixed_cash_fits(cash_out, order_value)
+                && Self::fixed_cash_fits(cash_out, projected.cash())
+            {
                 break;
             }
             quantity =
@@ -1934,11 +1974,15 @@ impl OmniMicroCapStrategy {
             next_cursor: date.and_time(self.intraday_execution_start_time()) + Duration::seconds(1),
         };
         let gross_amount = fill.price * fill.quantity as f64;
-        let cash_out = gross_amount + self.buy_commission(gross_amount);
-        if cash_out > projected.cash() + 1e-6 || cash_out > order_value + 1e-6 {
+        let cash_out = self.buy_cash_out(gross_amount);
+        if !Self::fixed_cash_fits(cash_out, projected.cash())
+            || !Self::fixed_cash_fits(cash_out, order_value)
+        {
             return 0;
         }
-        projected.apply_cash_delta(-cash_out);
+        projected
+            .apply_cash_delta(-cash_out)
+            .expect("projected buy cash must fit fixed-point ledger");
         projected
             .position_mut(symbol)
             .buy(date, fill.quantity, fill.price);
@@ -1994,12 +2038,14 @@ impl OmniMicroCapStrategy {
                     + Duration::seconds(1),
             });
         let gross_amount = fill.price * fill.quantity as f64;
-        let net_cash = gross_amount - self.sell_cost(date, gross_amount);
+        let net_cash = self.sell_net_cash(date, gross_amount);
         projected
             .position_mut(symbol)
             .sell(fill.quantity, fill.price)
             .ok()?;
-        projected.apply_cash_delta(net_cash);
+        projected
+            .apply_cash_delta(net_cash)
+            .expect("projected sell cash must fit fixed-point ledger");
         *execution_state
             .intraday_turnover
             .entry(symbol.to_string())
@@ -2144,7 +2190,9 @@ impl OmniMicroCapStrategy {
                         );
                         while take_qty > 0 {
                             let candidate_gross = execution_price * take_qty as f64;
-                            if gross_limit.is_some_and(|limit| candidate_gross > limit + 1e-6) {
+                            if gross_limit
+                                .is_some_and(|limit| !Self::fixed_cash_fits(candidate_gross, limit))
+                            {
                                 take_qty = self.decrement_order_quantity(
                                     take_qty,
                                     minimum_order_quantity,
@@ -2152,9 +2200,8 @@ impl OmniMicroCapStrategy {
                                 );
                                 continue;
                             }
-                            let candidate_cash =
-                                candidate_gross + self.buy_commission(candidate_gross);
-                            if candidate_cash <= cash + 1e-6 {
+                            let candidate_cash = self.buy_cash_out(candidate_gross);
+                            if Self::fixed_cash_fits(candidate_cash, cash) {
                                 break;
                             }
                             take_qty = self.decrement_order_quantity(
@@ -2254,7 +2301,9 @@ impl OmniMicroCapStrategy {
             if let Some(cash) = cash_limit {
                 while take_qty > 0 {
                     let candidate_gross = gross_amount + quote_price * take_qty as f64;
-                    if gross_limit.is_some_and(|limit| candidate_gross > limit + 1e-6) {
+                    if gross_limit
+                        .is_some_and(|limit| !Self::fixed_cash_fits(candidate_gross, limit))
+                    {
                         take_qty = self.decrement_order_quantity(
                             take_qty,
                             minimum_order_quantity,
@@ -2262,7 +2311,7 @@ impl OmniMicroCapStrategy {
                         );
                         continue;
                     }
-                    if candidate_gross + self.buy_commission(candidate_gross) <= cash + 1e-6 {
+                    if Self::fixed_cash_fits(self.buy_cash_out(candidate_gross), cash) {
                         break;
                     }
                     take_qty = self.decrement_order_quantity(
@@ -2870,8 +2919,8 @@ mod tests {
             .stamp_tax_rate_after_change = 0.0005;
         let strategy = OmniMicroCapStrategy::new(cfg);
 
-        assert!((strategy.buy_commission(100_000.0) - 30.0).abs() < 1e-9);
-        assert!((strategy.buy_commission(1_000.0) - 5.0).abs() < 1e-9);
+        assert!((strategy.buy_cost(100_000.0) - 30.0).abs() < 1e-9);
+        assert!((strategy.buy_cost(1_000.0) - 5.0).abs() < 1e-9);
         assert!(
             (strategy.sell_cost(NaiveDate::from_ymd_opt(2025, 1, 2).unwrap(), 100_000.0) - 80.0)
                 .abs()
diff --git a/crates/fidc-core/tests/corporate_actions.rs b/crates/fidc-core/tests/corporate_actions.rs
index 643a3f9..0e34073 100644
--- a/crates/fidc-core/tests/corporate_actions.rs
+++ b/crates/fidc-core/tests/corporate_actions.rs
@@ -368,11 +368,9 @@ fn engine_reinvests_dividend_receivable_in_round_lots() {
             first_date: buy_date,
         },
         BrokerSimulator::new_with_execution_price(
-            ChinaAShareCostModel {
-                commission_rate: 0.0008,
-                minimum_commission: 0.0,
-                ..ChinaAShareCostModel::default()
-            },
+            ChinaAShareCostModel::default()
+                .with_commission_rate(0.0008)
+                .with_minimum_commission(0.0),
             ChinaEquityRuleHooks::default(),
             PriceField::Open,
         ),
diff --git a/docs/engine-capability-roadmap.md b/docs/engine-capability-roadmap.md
index 789d6ce..cba2ca3 100644
--- a/docs/engine-capability-roadmap.md
+++ b/docs/engine-capability-roadmap.md
@@ -39,6 +39,7 @@ futures path. Confirmed aligned areas:
 | P0 | Futures intraday matching | Closed for daily/open/close, tick-price futures fills, and true multi-level order-book sweeping when optional `order_book_depth` data exists. L1-only data still uses the existing L1 matcher and is not inflated into fake depth. | Extend depth fields only if production vendors expose more levels or exchange-specific fields. |
 | P0 | Futures open-order lifecycle | Closed for futures pending limit orders, cross-day rematching, cancellation by id/symbol/all, and merged open-order runtime views. | Add more order status transitions only if UI requires extra intermediate event names. |
 | P0 | Combined multi-account NAV | Closed. `DailyEquityPoint`, progress events, and metrics use aggregate stock + futures initial cash and total equity. | None. |
+| P0 | Fixed-point execution money | Stock execution now freezes fee rates once and uses signed micro-yuan `i128` for gross amount, commission, stamp tax, transfer fee, strict budget checks, cash, liabilities, management fees, external flows and account units. Market indicators and return statistics remain `f64` outside the execution boundary. | Migrate position cost/PnL and the standalone futures cash ledger only after independent artifact and performance A/B gates. |
 | P1 | Futures trading parameter data source | Closed for engine-side trading-parameter ingestion/resolution via `futures_trading_parameters.csv` or component data. | Add more exchange metadata columns only when source data exposes them. |
 | P1 | Futures transaction cost decider | Closed. `FuturesTransactionCostModel` calculates by-money/by-volume open/close/close-today costs from trading parameters. | None. |
 | P1 | Futures settlement price mode | Closed. Engine supports configurable settlement price mode and resolves settlement/prev-settlement from factor fields with close/prev_close fallback. | Add dedicated settlement columns if the storage layer later separates them from factors. |
@@ -55,6 +56,8 @@ futures path. Confirmed aligned areas:
 - [x] Minute-level `time_rule` semantics including market-open, market-close,
       and physical-time style schedules.
 - [x] Fine-grained daily and minute execution quote strategy entrypoints.
+- [x] Stock broker fee, budget and cash-ledger arithmetic uses a micro-yuan
+      fixed-point execution primitive; one-micro over-budget orders fail.
 - [x] Scheduled actions evaluated against explicit intraday times.
 - [x] `update_universe`, `subscribe`, and `unsubscribe`.
 - [x] Intraday subscription guards at strategy API level; intraday execution uses minute quote semantics.