Explain rebalance denial reasons

crates/fidc-core/src/broker.rs

@@ -503,6 +503,42 @@ where
                 order_step_size,
             );
             let provisional_target_qty = desired_qty.clamp(min_target_qty, max_target_qty);
+            if desired_qty < current_qty
+                && min_target_qty >= current_qty
+                && diagnostics.len() < 16
+                && let Some(reason) = self.sell_target_denial_reason(
+                    date,
+                    portfolio,
+                    data,
+                    &symbol,
+                    current_qty,
+                    minimum_order_quantity,
+                    order_step_size,
+                )
+            {
+                diagnostics.push(format!(
+                    "rebalance_target_denied symbol={} side=sell reason={}",
+                    symbol, reason
+                ));
+            }
+            if desired_qty > current_qty
+                && max_target_qty <= current_qty
+                && diagnostics.len() < 16
+                && let Some(reason) = self.buy_target_denial_reason(
+                    date,
+                    portfolio,
+                    data,
+                    &symbol,
+                    current_qty,
+                    minimum_order_quantity,
+                    order_step_size,
+                )
+            {
+                diagnostics.push(format!(
+                    "rebalance_target_denied symbol={} side=buy reason={}",
+                    symbol, reason
+                ));
+            }
             if provisional_target_qty != desired_qty && diagnostics.len() < 16 {
                 diagnostics.push(format!(
                     "rebalance_target_clipped symbol={} desired={} min={} max={} provisional={}",
@@ -734,6 +770,92 @@ where
         gross - cost.total()
     }
 
+    fn sell_target_denial_reason(
+        &self,
+        date: NaiveDate,
+        portfolio: &PortfolioState,
+        data: &DataSet,
+        symbol: &str,
+        current_qty: u32,
+        minimum_order_quantity: u32,
+        order_step_size: u32,
+    ) -> Option<String> {
+        if current_qty == 0 {
+            return None;
+        }
+        let position = portfolio.position(symbol)?;
+        let snapshot = data.require_market(date, symbol).ok()?;
+        let candidate = data.require_candidate(date, symbol).ok()?;
+        let rule = self.rules.can_sell(
+            date,
+            snapshot,
+            candidate,
+            position,
+            self.execution_price_field,
+        );
+        if !rule.allowed {
+            return rule.reason;
+        }
+        let sellable = position.sellable_qty(date);
+        match self.market_fillable_quantity(
+            snapshot,
+            OrderSide::Sell,
+            sellable.min(current_qty),
+            minimum_order_quantity,
+            order_step_size,
+            0,
+            sellable >= current_qty,
+        ) {
+            Ok(quantity) => {
+                let quantity = quantity.min(sellable).min(current_qty);
+                if quantity == 0 {
+                    Some("no sellable quantity".to_string())
+                } else {
+                    None
+                }
+            }
+            Err(reason) => Some(reason),
+        }
+    }
+
+    fn buy_target_denial_reason(
+        &self,
+        date: NaiveDate,
+        _portfolio: &PortfolioState,
+        data: &DataSet,
+        symbol: &str,
+        current_qty: u32,
+        minimum_order_quantity: u32,
+        order_step_size: u32,
+    ) -> Option<String> {
+        let snapshot = data.require_market(date, symbol).ok()?;
+        let candidate = data.require_candidate(date, symbol).ok()?;
+        let rule = self
+            .rules
+            .can_buy(date, snapshot, candidate, self.execution_price_field);
+        if !rule.allowed {
+            return rule.reason;
+        }
+        match self.market_fillable_quantity(
+            snapshot,
+            OrderSide::Buy,
+            u32::MAX,
+            minimum_order_quantity,
+            order_step_size,
+            0,
+            false,
+        ) {
+            Ok(quantity) => {
+                if current_qty.saturating_add(quantity) <= current_qty {
+                    Some("no fillable buy quantity".to_string())
+                } else {
+                    None
+                }
+            }
+            Err(reason) => Some(reason),
+        }
+    }
+
     fn estimated_buy_cash_out(&self, date: NaiveDate, price: f64, quantity: u32) -> f64 {
         if quantity == 0 {
             return 0.0;

crates/fidc-core/tests/explicit_order_flow.rs

@@ -678,6 +678,22 @@ fn rebalance_optimizer_skips_unfunded_buy_when_existing_position_cannot_sell() {
             .unwrap_or(0),
         10_000
     );
+    assert!(
+        report
+            .diagnostics
+            .iter()
+            .any(|line| line.contains("rebalance_target_denied symbol=000001.SZ side=sell")),
+        "expected locked position denial diagnostics, got {:?}",
+        report.diagnostics
+    );
+    assert!(
+        report
+            .diagnostics
+            .iter()
+            .any(|line| line.contains("rebalance_buy_reduced symbol=000002.SZ")),
+        "expected unfunded buy reduction diagnostics, got {:?}",
+        report.diagnostics
+    );
 }
 
 #[test]