docs: Add Common Pitfall #41 - Stats API P&L recalculation bug

Documented the stats API bug where recalculating P&L from entry/exit
prices doesn't work for TP1+runner partial closes.

Issue:
- Stats showed -$26.10 when actual was +$46.97
- Recalculation used average exit price × full size
- Doesn't account for different TP1 vs runner exit prices

Fix:
- Use database realizedPnL field directly
- Database values corrected to match Drift UI TP1+runner sums
- Each trade shows as 2 lines in Drift (TP1 + runner)

Commits referenced:
- cd6f590: Corrected database P&L values
- d8b0307: Fixed stats API calculation

Lesson: Partial closes require storing combined P&L, can't
recalculate from average exit price.

.github/copilot-instructions.md

@@ -2049,7 +2049,58 @@ trade.realizedPnL += actualRealizedPnL  // NOT: result.realizedPnL from SDK
     - **Verification:** Container restart + new code = no more ghost accumulation possible
     - **Lesson:** Critical validation logic must NEVER skip during error conditions - use fallback methods that don't require the failing resource
 
-41. **Missing Telegram notifications for position closures (Fixed Nov 16, 2025):**
+41. **Stats API recalculating P&L incorrectly for TP1+runner trades (CRITICAL - Fixed Nov 19, 2025):**
+    - **Symptom:** Withdrawal stats page showing -$26.10 P&L when Drift UI shows +$46.97
+    - **Root Cause:** Stats API recalculating P&L from entry/exit prices, which doesn't work for TP1+runner partial closes
+    - **The Problem:**
+      * Each trade has 2 closes: TP1 (60-75%) at one price, runner (25-40%) at different price
+      * Database stores combined P&L from both closes in `realizedPnL` field
+      * Stats API used `positionSizeUSD × (exit - entry) / entry` formula
+      * But `exitPrice` is AVERAGE of TP1 and runner exits, not actual exit prices
+      * Formula: `(TP1_price × 0.6 + runner_price × 0.4) / 1.0` = average exit
+      * Result: Incorrect P&L calculation (-$26.10 vs actual +$46.97)
+    - **Real Example:**
+      * Trade: Entry $138.36 → TP1 $137.66 (60%) + Runner $136.94 (40%)
+      * Database: Combined P&L $54.19 (from Drift: $22.78 TP1 + $31.41 runner)
+      * Stats recalc: $8,326 × (136.96 - 138.36) / 138.36 = $83.94 (wrong!)
+      * Correct: Use database `realizedPnL` $54.19 directly
+    - **Drift UI shows 10 lines for 5 trades:**
+      * Each trade = 2 lines (TP1 close + runner close)
+      * Line 1: TP1 60% at $137.66 = $22.78
+      * Line 2: Runner 40% at $136.94 = $31.41
+      * Total: $54.19 (stored in database `realizedPnL`)
+    - **Fix (Nov 19, 2025):**
+      ```typescript
+      // BEFORE (BROKEN - recalculated from entry/exit):
+      const totalPnL = trades.reduce((sum, trade) => {
+        const correctPnL = trade.positionSizeUSD * (
+          trade.direction === 'long'
+            ? (trade.exitPrice - trade.entryPrice) / trade.entryPrice
+            : (trade.entryPrice - trade.exitPrice) / trade.entryPrice
+        )
+        return sum + correctPnL
+      }, 0)
+      
+      // AFTER (FIXED - use database realizedPnL):
+      const totalPnL = trades.reduce((sum, trade) => {
+        return sum + Number(trade.realizedPnL)
+      }, 0)
+      ```
+    - **Database P&L Correction (Nov 19, 2025):**
+      * Corrected inflated P&L values to match Drift UI actual TP1+runner sums
+      * Trade cmi5p09y: 37.67 → 38.90 (TP1 $9.72 + runner $29.18)
+      * Trade cmi5ie3c: 59.35 → 40.09 (TP1 $21.67 + runner $18.42)
+      * Trade cmi5a6jm: 19.79 → 13.72 (TP1 $1.33 + runner $4.08 + $8.31)
+      * v8 total: $46.97 (matches Drift UI exactly)
+      * Commit: cd6f590 "fix: Correct v8 trade P&L to match Drift UI actual values"
+    - **Impact:** Stats page now shows accurate v8 performance (+$46.97)
+    - **Files Changed:**
+      * `app/api/withdrawals/stats/route.ts` - Use `realizedPnL` not recalculation
+      * Added debug logging: "📊 Stats API: Found X closed trades"
+      * Commit: d8b0307 "fix: Use database realizedPnL instead of recalculating"
+    - **Lesson:** When trades have partial closes (TP1/TP2/runner), the database `realizedPnL` is the source of truth. Entry/exit price calculations only work for full position closes. Average exit price × full size ≠ sum of partial close P&Ls.
+
+42. **Missing Telegram notifications for position closures (Fixed Nov 16, 2025):**
     - **Symptom:** Position Manager closes trades (TP/SL/manual) but user gets no immediate notification
     - **Root Cause:** TODO comment in Position Manager for Telegram notifications, never implemented
     - **Impact:** User unaware of P&L outcomes until checking dashboard or Drift UI manually