docs: Add Common Pitfall #59 - Layer 2 duplicate Telegram notifications
Bug: Trade #8 (SHORT SOL-PERP, Nov 22, 04:05) sent 13 duplicate notifications
- P&L compounded $11.50 → $155.05 (8.2× actual $18.79)
- Root cause: Layer 2 ghost detection ignored closingInProgress flag
- Rate limit storm: 6,581 failures → Layer 2 triggered 13 times
- Each call sent notification before async DB update completed
Real incident details:
- TP1: +$32.63 (60% closed)
- Runner: -$13.84 (40% closed at breakeven)
- Net: +$18.79 (Drift confirmed)
- Database showed $155.05 (manually corrected)
Fix: Added closingInProgress check before Layer 2 ghost detection
Related: Pitfalls #40 (death spiral), #48 (closingInProgress), #49 (compounding)
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