fix: normalize symbol comparison to prevent duplicate data in AI input

Use market.Normalize() for both position and candidate symbols to handle
different formats (ETH vs ETHUSDT), ensuring positions are correctly
excluded from candidate list.

decision/engine.go

@@ -986,14 +986,17 @@ func (e *StrategyEngine) BuildUserPrompt(ctx *Context) string {
 	// Candidate coins (exclude coins already in positions to avoid duplicate data)
 	positionSymbols := make(map[string]bool)
 	for _, pos := range ctx.Positions {
-		positionSymbols[pos.Symbol] = true
+		// Normalize symbol to handle both "ETH" and "ETHUSDT" formats
+		normalizedSymbol := market.Normalize(pos.Symbol)
+		positionSymbols[normalizedSymbol] = true
 	}
 
 	sb.WriteString(fmt.Sprintf("## Candidate Coins (%d coins)\n\n", len(ctx.MarketDataMap)))
 	displayedCount := 0
 	for _, coin := range ctx.CandidateCoins {
 		// Skip if this coin is already a position (data already shown in positions section)
-		if positionSymbols[coin.Symbol] {
+		normalizedCoinSymbol := market.Normalize(coin.Symbol)
+		if positionSymbols[normalizedCoinSymbol] {
 			continue
 		}