critical: Fix ghost detection P&L compounding - delete from Map BEFORE check

Bug: Multiple monitoring loops detect ghost simultaneously
- Loop 1: has(tradeId) → true → proceeds
- Loop 2: has(tradeId) → true → ALSO proceeds (race condition)
- Both send Telegram notifications with compounding P&L

Real incident (Dec 2, 2025):
- Manual SHORT at $138.84
- 23 duplicate notifications
- P&L compounded: -$47.96 → -$1,129.24 (23× accumulation)
- Database shows single trade with final compounded value

Fix: Map.delete() returns true if key existed, false if already removed
- Call delete() FIRST
- Check return value
 proceeds
- All other loops get false → skip immediately
- Atomic operation prevents race condition

Pattern: This is variant of Common Pitfalls #48, #49, #59, #60, #61
- All had "check then delete" pattern
- All vulnerable to async timing issues
- Solution: "delete then check" pattern
- Map.delete() is synchronous and atomic

Files changed:
- lib/trading/position-manager.ts lines 390-410

Related: DUPLICATE PREVENTED message was working but too late

lib/trading/position-manager.ts

@@ -390,14 +390,23 @@ export class PositionManager {
   private async handleExternalClosure(trade: ActiveTrade, reason: string): Promise<void> {
     console.log(`🧹 Handling external closure: ${trade.symbol} (${reason})`)
     
-    // CRITICAL: Check if already processed to prevent duplicate notifications
+    // CRITICAL FIX (Dec 2, 2025): Remove from activeTrades FIRST, then check if already removed
+    // Bug: Multiple monitoring loops detect ghost simultaneously
+    // - Loop 1 checks has(tradeId) → true → proceeds
+    // - Loop 2 checks has(tradeId) → true → also proceeds (RACE CONDITION)
+    // - Both send Telegram notifications with compounding P&L
+    // Fix: Delete BEFORE check, so only first loop proceeds
     const tradeId = trade.id
-    if (!this.activeTrades.has(tradeId)) {
+    const wasInMap = this.activeTrades.delete(tradeId)
+    
+    if (!wasInMap) {
       console.log(`⚠️ DUPLICATE PREVENTED: Trade ${tradeId} already processed, skipping`)
       console.log(`   This prevents duplicate Telegram notifications with compounding P&L`)
       return
     }
     
+    console.log(`🗑️ Removed ${trade.symbol} from monitoring (will not process duplicates)`)
+    
     // CRITICAL: Calculate P&L using originalPositionSize for accuracy
     // currentSize may be stale if Drift propagation was interrupted
     const profitPercent = this.calculateProfitPercent(
@@ -410,10 +419,6 @@ export class PositionManager {
     
     console.log(`💰 Estimated P&L: ${profitPercent.toFixed(2)}% on $${sizeForPnL.toFixed(2)} → $${estimatedPnL.toFixed(2)}`)
     
-    // Remove from monitoring IMMEDIATELY to prevent race conditions
-    this.activeTrades.delete(tradeId)
-    console.log(`🗑️ Removed ${trade.symbol} from monitoring`)
-    
     // Update database
     try {
       const holdTimeSeconds = Math.floor((Date.now() - trade.entryTime) / 1000)