Fix 8 bugs from code review

B#1 — sigCh shared across goroutines, SIGINT unreliable
  → context.WithCancel: main loop cancels ctx on SIGINT,
    4 WS goroutines select on ctx.Done() instead of shared sigCh

B#3 — restoreOpenPositions missing LastScaleAt
  → Set LastScaleAt = tr.OpenedAt on restore so scale-in cooldown works

B#4 — dYdX heartbeat goroutine leaks on reconnect
  → Added stopHeartbeat chan + heartbeatMu mutex; close old channel
    before spawning new heartbeat goroutine

B#5 — GetBitgetSize fmt.Sprintf rounds up, may exceed amountUSD
  → Added math.Floor(sz*multiplier)/multiplier before format to round
    DOWN to nearest valid step size for every coin

B#6 — netProfit and CalcNetProfit duplicate formula
  → scanner.go netProfit now delegates to exchange.CalcNetProfit

B#7 — Aevo Run callback only 2 params, incompatible with startExchange
  → Changed to 4-arg callback func(coin, price, bid, ask) with bid=ask=0

B#8 — parseFloat uses fmt.Sscanf (slow, locale-sensitive)
  → Replaced with strconv.ParseFloat

B#9 — dYdX receives hlSymbols instead of its own symbol list
  → Added dydxSymbols var, built from c.HL like other exchanges

exchange/aevo.go

@@ -47,7 +47,7 @@ func NewAevoWS(tracked []TrackedSymbol) *AevoWS {
 }
 
 // Run connects to Aevo WS and streams ticker data.
-func (a *AevoWS) Run(updateFn func(coin string, price float64)) error {
+func (a *AevoWS) Run(updateFn func(coin string, price, bid, ask float64)) error {
 	a.Conn.OnConnect = func() {
 		log.Printf("[Aevo WS] Connected, subscribing to %d tickers", len(a.Tracked))
 
@@ -120,7 +120,7 @@ func (a *AevoWS) Run(updateFn func(coin string, price float64)) error {
 			}
 
 			if price > 0 {
-				updateFn(coin, price)
+				updateFn(coin, price, 0, 0) // B#7: pass bid=ask=0 for 4-arg signature
 			}
 		}
 	}

exchange/bitget_trade.go

@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"math"
 	"net/http"
 	"strings"
 	"time"
@@ -95,6 +96,7 @@ func (b *BitgetTrade) sign(method, requestPath, timestamp, body string) string {
 // GetBitgetSize calculates the contract size for a given USD amount.
 // Returns size as a decimal string complying with Bitget's USDT-FUTURES precision.
 // Enforces the exchange's minimum: minTradeNum contracts AND $5 min notional.
+// Uses math.Floor to round DOWN to the nearest valid step (B#5: prevent rounding up).
 func GetBitgetSize(symbol string, amountUSD, price float64) string {
 	if amountUSD < 5 {
 		amountUSD = 5 // Bitget minimum notional
@@ -106,28 +108,34 @@ func GetBitgetSize(symbol string, amountUSD, price float64) string {
 		if sz < 1 {
 			sz = 1
 		}
+		sz = math.Floor(sz) // step=1
 		return fmt.Sprintf("%.0f", sz) // minTradeNum=1, sizeMultiplier=1
 	case "LINKUSDT":
 		if sz < 1 {
 			sz = 1
 		}
+		sz = math.Floor(sz) // step=1
 		return fmt.Sprintf("%.0f", sz) // minTradeNum=1, sizeMultiplier=1
 	case "ONDOUSDT":
+		sz = math.Floor(sz*10) / 10 // step=0.1
 		if sz < 0.1 {
 			sz = 0.1
 		}
 		return fmt.Sprintf("%.1f", sz) // minTradeNum=0.1, sizeMultiplier=0.1
 	case "OPUSDT":
+		sz = math.Floor(sz*10) / 10 // step=0.1
 		if sz < 0.1 {
 			sz = 0.1
 		}
 		return fmt.Sprintf("%.1f", sz) // minTradeNum=0.1, sizeMultiplier=0.1
 	case "WIFUSDT":
+		sz = math.Floor(sz*10) / 10 // step=0.1
 		if sz < 0.1 {
 			sz = 0.1
 		}
 		return fmt.Sprintf("%.1f", sz) // minTradeNum=0.1, sizeMultiplier=0.1
 	case "ARBUSDT":
+		sz = math.Floor(sz*100) / 100 // step=0.01
 		if sz < 0.01 {
 			sz = 0.01
 		}

exchange/connector.go

@@ -1,8 +1,8 @@
 package exchange
 
 import (
-	"fmt"
 	"log"
+	"strconv"
 	"time"
 
 	"github.com/gorilla/websocket"
@@ -148,9 +148,10 @@ func (pc *PriceConnector) SendJSON(v interface{}) error {
 }
 
 // Helper: parse float from string
+// B#8: use strconv.ParseFloat instead of fmt.Sscanf
 func parseFloat(s string) float64 {
-	var f float64
-	if _, err := fmt.Sscanf(s, "%f", &f); err != nil {
+	f, err := strconv.ParseFloat(s, 64)
+	if err != nil {
 		return 0
 	}
 	return f

exchange/dydx.go

@@ -3,13 +3,16 @@ package exchange
 import (
 	"encoding/json"
 	"log"
+	"sync"
 	"time"
 )
 
 // DydxWS connects to dYdX v4 WebSocket for market data (oracle prices).
 type DydxWS struct {
-	Conn    *PriceConnector
-	Tracked []string // coin names like ["BTC", "ETH", ...]
+	Conn          *PriceConnector
+	Tracked       []string // coin names like ["BTC", "ETH", ...]
+	stopHeartbeat chan struct{}
+	heartbeatMu   sync.Mutex
 }
 
 type dydxSubscribeMsg struct {
@@ -53,6 +56,15 @@ func (d *DydxWS) Run(updateFn func(coin string, price, bid, ask float64)) error
 			log.Printf("[dYdX WS] Subscribe error: %v", err)
 		}
 
+		// B#4: Stop any previous heartbeat goroutine before starting a new one
+		d.heartbeatMu.Lock()
+		if d.stopHeartbeat != nil {
+			close(d.stopHeartbeat)
+		}
+		d.stopHeartbeat = make(chan struct{})
+		hbStop := d.stopHeartbeat
+		d.heartbeatMu.Unlock()
+
 		// dYdX requires JSON {"type":"ping"} every ~30s
 		go func() {
 			heartbeat := time.NewTicker(15 * time.Second)
@@ -65,6 +77,8 @@ func (d *DydxWS) Run(updateFn func(coin string, price, bid, ask float64)) error
 					if err := d.Conn.SendJSON(map[string]string{"type": "ping"}); err != nil {
 						log.Printf("[dYdX WS] Heartbeat send error: %v", err)
 					}
+				case <-hbStop:
+					return
 				case <-d.Conn.Done():
 					return
 				}