def _extract_trades_from_df(self, df):
        """Extract entry/exit trades from a per-bar signal DataFrame (for vectorized version)."""
        trades = []
        prev = 0
        entry_price = None
        entry_time = None
        for ts, row in df.iterrows():
            sig = row.signal
            sp  = row.spread
            if sig ==  1 and prev <= 0:
                entry_price = sp
                entry_time = ts
            if sig ==  0 and prev == 1 and entry_price is not None:
                trades.append({
                    "entry_time":  entry_time,
                    "exit_time":   ts,
                    "entry_price": entry_price,
                    "exit_price":  sp,
                    "pnl":         (sp - entry_price) * self.trade_size,
                    "side":        "long"
                })
            if sig == -1 and prev >= 0:
                entry_price = sp
                entry_time = ts
            if sig ==  0 and prev == -1 and entry_price is not None:
                trades.append({
                    "entry_time":  entry_time,
                    "exit_time":   ts,
                    "entry_price": entry_price,
                    "exit_price":  sp,
                    "pnl":         (entry_price - sp) * self.trade_size,
                    "side":        "short"
                })
            prev = sig
        return pd.DataFrame(trades)