it might be better

src/backtester.rs

@@ -199,12 +199,12 @@ impl Backtester {
         let shares =
             self.strategy
                 .calculate_position_size(price, portfolio_value, available_cash, signal);
-        if shares == 0 {
+        if shares <= 0.0 {
             return false;
         }
 
         let fill_price = Self::apply_slippage(price, "buy");
-        let cost = shares as f64 * fill_price;
+        let cost = shares * fill_price;
         if cost > self.cash {
             return false;
         }
@@ -214,7 +214,7 @@ impl Backtester {
             symbol.to_string(),
             BacktestPosition {
                 symbol: symbol.to_string(),
-                shares: shares as f64,
+                shares: shares,
                 entry_price: fill_price,
                 entry_time: timestamp,
                 entry_atr: signal.atr,
@@ -229,7 +229,7 @@ impl Backtester {
         self.trades.push(Trade {
             symbol: symbol.to_string(),
             side: "BUY".to_string(),
-            shares: shares as f64,
+            shares: shares,
             price: fill_price,
             timestamp,
             pnl: 0.0,

src/bot.rs

@@ -452,12 +452,12 @@ impl TradingBot {
 
     // ── Volatility-adjusted position sizing ──────────────────────────
 
-    async fn calculate_position_size(&self, signal: &TradeSignal) -> u64 {
+    async fn calculate_position_size(&self, signal: &TradeSignal) -> f64 {
         let account = match self.client.get_account().await {
             Ok(a) => a,
             Err(e) => {
                 tracing::error!("Failed to get account: {}", e);
-                return 0;
+                return 0.0;
             }
         };
 
@@ -557,14 +557,14 @@ impl TradingBot {
         }
 
         let shares = self.calculate_position_size(signal).await;
-        if shares == 0 {
+        if shares <= 0.0 {
             tracing::info!("{}: Insufficient funds for purchase", symbol);
             return false;
         }
 
         match self
             .client
-            .submit_market_order(symbol, shares as f64, "buy")
+            .submit_market_order(symbol, shares, "buy")
             .await
         {
             Ok(order) => {

src/strategy.rs

@@ -33,9 +33,9 @@ impl Strategy {
         portfolio_value: f64,
         available_cash: f64,
         signal: &TradeSignal,
-    ) -> u64 {
+    ) -> f64 {
         if available_cash <= 0.0 {
-            return 0;
+            return 0.0;
         }
 
         let position_value = if signal.atr_pct > MIN_ATR_PCT {
@@ -51,7 +51,9 @@ impl Strategy {
         };
 
         let position_value = position_value.min(available_cash);
-        (position_value / price).floor() as u64
+        // Use fractional shares — Alpaca supports them for paper trading.
+        // Truncate to 4 decimal places to avoid floating point dust.
+        ((position_value / price) * 10000.0).floor() / 10000.0
     }
 
     /// Check if stop-loss, trailing stop, or time exit should trigger.