Add complete Ouroboros trading system with TDD test suite

Implement the full autonomous trading agent architecture:
- KIS broker with async API, token refresh, leaky bucket rate limiter, and hash key signing
- Gemini-powered decision engine with JSON parsing and confidence threshold enforcement
- Risk manager with circuit breaker (-3% P&L) and fat finger protection (30% cap)
- Evolution engine for self-improving strategy generation via failure analysis
- 35 passing tests written TDD-first covering risk, broker, and brain modules
- CI/CD pipeline, Docker multi-stage build, and AI agent context docs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/core/risk_manager.py

@@ -0,0 +1,84 @@
+"""Risk management — the Shield that protects the portfolio.
+
+This module is READ-ONLY by policy (see docs/agents.md).
+Changes require human approval and two passing test suites.
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass
+
+from src.config import Settings
+
+logger = logging.getLogger(__name__)
+
+
+class CircuitBreakerTripped(SystemExit):
+    """Raised when daily P&L loss exceeds the allowed threshold."""
+
+    def __init__(self, pnl_pct: float, threshold: float) -> None:
+        self.pnl_pct = pnl_pct
+        self.threshold = threshold
+        super().__init__(
+            f"CIRCUIT BREAKER: Daily P&L {pnl_pct:.2f}% exceeded "
+            f"threshold {threshold:.2f}%. All trading halted."
+        )
+
+
+class FatFingerRejected(Exception):
+    """Raised when an order exceeds the maximum allowed proportion of cash."""
+
+    def __init__(self, order_amount: float, total_cash: float, max_pct: float) -> None:
+        self.order_amount = order_amount
+        self.total_cash = total_cash
+        self.max_pct = max_pct
+        ratio = (order_amount / total_cash * 100) if total_cash > 0 else float("inf")
+        super().__init__(
+            f"FAT FINGER: Order {order_amount:,.0f} is {ratio:.1f}% of "
+            f"cash {total_cash:,.0f} (max allowed: {max_pct:.1f}%)."
+        )
+
+
+class RiskManager:
+    """Pre-order risk gate that enforces circuit breaker and fat-finger checks."""
+
+    def __init__(self, settings: Settings) -> None:
+        self._cb_threshold = settings.CIRCUIT_BREAKER_PCT
+        self._ff_max_pct = settings.FAT_FINGER_PCT
+
+    def check_circuit_breaker(self, current_pnl_pct: float) -> None:
+        """Halt trading if daily loss exceeds the threshold.
+
+        The threshold is inclusive: exactly -3.0% is allowed, but -3.01% is not.
+        """
+        if current_pnl_pct < self._cb_threshold:
+            logger.critical(
+                "Circuit breaker tripped",
+                extra={"pnl_pct": current_pnl_pct},
+            )
+            raise CircuitBreakerTripped(current_pnl_pct, self._cb_threshold)
+
+    def check_fat_finger(self, order_amount: float, total_cash: float) -> None:
+        """Reject orders that exceed the maximum proportion of available cash."""
+        if total_cash <= 0:
+            raise FatFingerRejected(order_amount, total_cash, self._ff_max_pct)
+
+        ratio_pct = (order_amount / total_cash) * 100
+        if ratio_pct > self._ff_max_pct:
+            logger.warning(
+                "Fat finger check failed",
+                extra={"order_amount": order_amount},
+            )
+            raise FatFingerRejected(order_amount, total_cash, self._ff_max_pct)
+
+    def validate_order(
+        self,
+        current_pnl_pct: float,
+        order_amount: float,
+        total_cash: float,
+    ) -> None:
+        """Run all pre-order risk checks. Raises on failure."""
+        self.check_circuit_breaker(current_pnl_pct)
+        self.check_fat_finger(order_amount, total_cash)
+        logger.info("Order passed risk validation")