diff --git a/crates/fidc-core/src/stock_pool_execution.rs b/crates/fidc-core/src/stock_pool_execution.rs
index fd673a8..bf5018f 100644
--- a/crates/fidc-core/src/stock_pool_execution.rs
+++ b/crates/fidc-core/src/stock_pool_execution.rs
@@ -1588,7 +1588,17 @@ pub fn build_stock_pool_target_plan_with_fee_model(
         if sizing_price <= Decimal::ZERO {
             return Err(format!("{symbol} execution sizing price is invalid"));
         }
-        let raw_target = (target_value / sizing_price).floor();
+        // Existing shares are marked at the observed market price. Only the
+        // new buy leg pays its executable/slippage price; repricing the whole
+        // position would charge fictitious slippage and miss a board lot.
+        let current_value = current_quantity * quote.last_price;
+        let raw_target = if target_value >= current_value {
+            current_quantity + ((target_value - current_value) / sizing_price).floor()
+        } else {
+            // Sale slippage changes proceeds, not the marked shares we must
+            // remove to reach a market-value target.
+            (target_value / quote.last_price).floor()
+        };
         let (step, minimum_buy) = order_quantity_rules(quote)?;
         let mut target_quantity = current_quantity;
         let mut delta = Decimal::ZERO;
@@ -1911,7 +1921,7 @@ pub fn build_stock_pool_target_plan_with_fee_model(
         let cost = |quantity: Decimal| {
             Ok(quantity * price + fee_for(&row.symbol, OrderSide::Buy, quantity * price)?)
         };
-        let own_budget = (row.target_value - row.current_quantity * price).max(Decimal::ZERO);
+        let own_budget = (row.target_value - row.current_quantity * quote.last_price).max(Decimal::ZERO);
         let allocation_quantity = max_affordable_buy_quantity_with_cost(
             own_budget,
             row.delta_quantity,
diff --git a/crates/fidc-core/src/stock_pool_execution_tests.rs b/crates/fidc-core/src/stock_pool_execution_tests.rs
index b3e0dd5..d43694e 100644
--- a/crates/fidc-core/src/stock_pool_execution_tests.rs
+++ b/crates/fidc-core/src/stock_pool_execution_tests.rs
@@ -2,12 +2,12 @@ use super::*;
 
 #[test]
 fn equal_thirty_seats_use_full_precision_at_a_board_lot_boundary() {
-    for (equity, price, held) in [("999377.147617", "3.070307", 2000), ("995624.8819", "6.420642", 900)] {
+    for (equity, price, executable, held) in [("999377.147617", "3.07", "3.070307", 2000), ("995624.8819", "6.42", "6.420642", 900)] {
         let pool = members(30);
         let mut market = quotes(30);
         let last = market.last_mut().unwrap();
         last.last_price = price.parse().unwrap();
-        last.buy_sizing_price = Some(last.last_price);
+        last.buy_sizing_price = Some(executable.parse().unwrap());
         let positions = vec![Position { symbol: last.symbol.clone(), quantity: held.into(), closable_quantity: held.into(), average_cost: last.last_price }];
         let mut selection = selection(30, 30);
         let constraints = StockPoolDecisionConstraints { target_holding_count: Some(30), reserve_cash_slots: 1, ..Default::default() };
@@ -32,6 +32,19 @@ fn equal_thirty_seats_use_full_precision_at_a_board_lot_boundary() {
         assert_eq!(state, restored);
     }
 }
+
+#[test]
+fn sale_slippage_does_not_prevent_a_marked_value_board_lot_reduction() {
+    let pool = members(1);
+    let mut market = quotes(1);
+    market[0].sell_sizing_price = Some(Decimal::new(99,1));
+    let positions = vec![Position { symbol:symbol(1),quantity:200.into(),closable_quantity:200.into(),average_cost:10.into() }];
+    let plan = build_stock_pool_target_plan_with_constraints(&selection(1,1),&pool,&StockPoolExecutionRule::default(),
+        &AccountSnapshot {total_equity:2000.into(),cash:Decimal::ZERO,frozen_cash:Decimal::ZERO},&positions,&market,
+        5000,Decimal::ZERO,"hold","full_rebalance",&StockPoolDecisionConstraints::default(),"reduce",Decimal::ZERO,Decimal::ZERO,Decimal::ZERO).unwrap();
+    assert_eq!(plan.rows[0].target_value,Decimal::from(1000));
+    assert_eq!(plan.rows[0].delta_quantity,Decimal::from(-100));
+}
 use serde_json::json;
 
 fn symbol(index: usize) -> String {
diff --git a/docs/stock-pool-ratio-precision-20260919.md b/docs/stock-pool-ratio-precision-20260919.md
index bb158de..0a9d70c 100644
--- a/docs/stock-pool-ratio-precision-20260919.md
+++ b/docs/stock-pool-ratio-precision-20260919.md
@@ -2,6 +2,8 @@
 
 此前按10000整数基点分配等权，然后反算资金。30只股票的333/334基点并不等于1/30，在临界整手处会漏补仓。修复将 `target_weight_bps` 保留为展示/旧数据合同，新增独立 `target_weight_ratios` 计算预算。
 
+临界样例同时复现了第二个错误：原持仓按含买入滑点的价格重新估值，将未发生交易的滑点也扣进可买预算。补仓现在用目标市值减去原持仓行情市值，再按新买入价格和费用计算；卖出滑点只改变回款，不改变待减少的行情市值股数。
+
 停牌持仓优先保留已记录的高精度比例；旧状态只有整数基点时保留已证明的旧预算，不反猜精确1/N。退出、候补、保护席位、指数仓位、资金预留和显式部分权重保留原规则。实际下单数量仍经过资金/费用、整手、T+1及风控检查。
 
 执行状态新增 `last_target_weight_ratios`，首次记录精确比例升级schema2。旧schema1可读但不得携带新比例字段；旧消费者应拒绝新状态，回滚不能删除或降精度重写状态。回测、Paper、Live及Strategy Runtime都必须共同消费该比例，ETF顺延目标也携带相同比例。