feat: add margin call / stop-out simulation

STOP_OUT_PCT env var (default 0.0 = Exness standard: stop at $0 equity).
- During open trade: checks worst-case equity (candle.low/high) each candle
- Before new trade: checks balance > stop_out_balance
- Prints STOP-OUT event in trade log and MARGIN CALL banner in summary

Portfolio simulator updated: checks combined balance vs stop-out level.

Findings:
  1% risk — never margin-called at any stop-out level
  5% XAUUSDm — MARGIN CALL at STOP_OUT_PCT=0.2 (balance hit $88.99 < $120)
  5% XAGUSDm/BTC/Oil — survive 20% stop-out (lower early drawdown)
  Portfolio 4 pairs — no margin call at 20% stop-out (diversification)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/portfolio_sim.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+"""
+Portfolio simulator — combines trade logs from multiple Ares backtest runs
+into a single compounding account, sorted chronologically by open time.
+
+Usage: python3 scripts/portfolio_sim.py < combined_trades.txt
+Env:   STOP_OUT_PCT=0.0 (fraction of initial balance, e.g. 0.2 = stop at $120 on $600)
+"""
+
+import sys
+import os
+import re
+from decimal import Decimal
+
+TRADE_RE = re.compile(
+    r'\[(\d{4}-\d{2}-\d{2} \d{2}:\d{2}) \S+\].*?pnl=([+-]?\d+\.\d+) bal=(\d+\.\d+)'
+)
+
+def parse_trades(lines):
+    trades = []
+    for line in lines:
+        m = TRADE_RE.search(line)
+        if not m:
+            continue
+        open_time  = m.group(1)
+        pnl_abs    = Decimal(m.group(2))
+        bal_after  = Decimal(m.group(3))
+        bal_before = bal_after - pnl_abs
+        if bal_before <= 0:
+            continue
+        pnl_ratio = pnl_abs / bal_before
+        trades.append((open_time, pnl_ratio))
+    return trades
+
+def simulate(trades, start_balance=Decimal("600"), stop_out_pct=Decimal("0.0")):
+    trades_sorted  = sorted(trades, key=lambda t: t[0])
+    stop_out_bal   = start_balance * stop_out_pct
+
+    balance        = start_balance
+    peak           = balance
+    max_dd         = Decimal("0")
+    wins = losses  = 0
+    margin_called  = False
+
+    for open_time, pnl_ratio in trades_sorted:
+        if balance <= stop_out_bal:
+            print(f"  *** MARGIN CALL at {open_time}: balance ${balance:.2f} ≤ stop-out ${stop_out_bal:.2f} ***")
+            margin_called = True
+            break
+
+        pnl      = balance * pnl_ratio
+        balance += pnl
+        if balance > peak:
+            peak = balance
+        dd = balance - peak
+        if dd < max_dd:
+            max_dd = dd
+        if pnl >= 0:
+            wins  += 1
+        else:
+            losses += 1
+
+    total = wins + losses
+    wr    = wins / total * 100 if total else 0
+    ret   = (balance - start_balance) / start_balance * 100
+
+    print("─" * 47)
+    print(f"  Combined Portfolio (all pairs)")
+    print("─" * 47)
+    print(f"  Stop-out level : {float(stop_out_pct)*100:.0f}% of initial (${stop_out_bal:.2f})")
+    print(f"  Trades         : {total}  (W={wins} L={losses}  WR={wr:.1f}%)")
+    print(f"  Start balance  : ${start_balance:,.2f}")
+    print(f"  Final balance  : ${balance:,.2f}")
+    print(f"  Total return   : {ret:+,.1f}%")
+    print(f"  Max drawdown   : ${max_dd:,.2f}  ({float(max_dd/peak)*100:.1f}% of peak)")
+    if margin_called:
+        print(f"  *** MARGIN CALL triggered ***")
+    print("─" * 47)
+
+if __name__ == "__main__":
+    lines        = sys.stdin.readlines()
+    trades       = parse_trades(lines)
+    start_bal    = Decimal(os.environ.get("BACKTEST_BALANCE", "600"))
+    stop_out_pct = Decimal(os.environ.get("STOP_OUT_PCT", "0.0"))
+    if not trades:
+        print("No trades found in input.")
+        sys.exit(1)
+    simulate(trades, start_balance=start_bal, stop_out_pct=stop_out_pct)