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>

tests/test_brain.py

@@ -0,0 +1,159 @@
+"""TDD tests for brain/gemini_client.py — written BEFORE implementation."""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from src.brain.gemini_client import GeminiClient, TradeDecision
+
+
+# ---------------------------------------------------------------------------
+# Response Parsing
+# ---------------------------------------------------------------------------
+
+
+class TestResponseParsing:
+    """Gemini responses must be parsed into validated TradeDecision objects."""
+
+    def test_valid_buy_response(self, settings):
+        client = GeminiClient(settings)
+        raw = '{"action": "BUY", "confidence": 90, "rationale": "Strong momentum"}'
+        decision = client.parse_response(raw)
+        assert decision.action == "BUY"
+        assert decision.confidence == 90
+        assert decision.rationale == "Strong momentum"
+
+    def test_valid_sell_response(self, settings):
+        client = GeminiClient(settings)
+        raw = '{"action": "SELL", "confidence": 85, "rationale": "Overbought RSI"}'
+        decision = client.parse_response(raw)
+        assert decision.action == "SELL"
+
+    def test_valid_hold_response(self, settings):
+        client = GeminiClient(settings)
+        raw = '{"action": "HOLD", "confidence": 95, "rationale": "Sideways market"}'
+        decision = client.parse_response(raw)
+        assert decision.action == "HOLD"
+
+
+# ---------------------------------------------------------------------------
+# Confidence Threshold Enforcement
+# ---------------------------------------------------------------------------
+
+
+class TestConfidenceThreshold:
+    """If confidence < 80, the action MUST be forced to HOLD."""
+
+    def test_low_confidence_buy_becomes_hold(self, settings):
+        client = GeminiClient(settings)
+        raw = '{"action": "BUY", "confidence": 65, "rationale": "Weak signal"}'
+        decision = client.parse_response(raw)
+        assert decision.action == "HOLD"
+        assert decision.confidence == 65
+
+    def test_low_confidence_sell_becomes_hold(self, settings):
+        client = GeminiClient(settings)
+        raw = '{"action": "SELL", "confidence": 79, "rationale": "Uncertain"}'
+        decision = client.parse_response(raw)
+        assert decision.action == "HOLD"
+
+    def test_exactly_threshold_is_allowed(self, settings):
+        client = GeminiClient(settings)
+        raw = '{"action": "BUY", "confidence": 80, "rationale": "Just enough"}'
+        decision = client.parse_response(raw)
+        assert decision.action == "BUY"
+
+
+# ---------------------------------------------------------------------------
+# Malformed JSON Handling
+# ---------------------------------------------------------------------------
+
+
+class TestMalformedJsonHandling:
+    """Gemini may return garbage — the parser must not crash."""
+
+    def test_empty_string_returns_hold(self, settings):
+        client = GeminiClient(settings)
+        decision = client.parse_response("")
+        assert decision.action == "HOLD"
+        assert decision.confidence == 0
+
+    def test_plain_text_returns_hold(self, settings):
+        client = GeminiClient(settings)
+        decision = client.parse_response("I think you should buy Samsung stock")
+        assert decision.action == "HOLD"
+        assert decision.confidence == 0
+
+    def test_partial_json_returns_hold(self, settings):
+        client = GeminiClient(settings)
+        decision = client.parse_response('{"action": "BUY", "confidence":')
+        assert decision.action == "HOLD"
+        assert decision.confidence == 0
+
+    def test_json_with_missing_fields_returns_hold(self, settings):
+        client = GeminiClient(settings)
+        decision = client.parse_response('{"action": "BUY"}')
+        assert decision.action == "HOLD"
+        assert decision.confidence == 0
+
+    def test_json_with_invalid_action_returns_hold(self, settings):
+        client = GeminiClient(settings)
+        decision = client.parse_response(
+            '{"action": "YOLO", "confidence": 99, "rationale": "moon"}'
+        )
+        assert decision.action == "HOLD"
+        assert decision.confidence == 0
+
+    def test_json_wrapped_in_markdown_code_block(self, settings):
+        """Gemini often wraps JSON in ```json ... ``` blocks."""
+        client = GeminiClient(settings)
+        raw = '```json\n{"action": "BUY", "confidence": 92, "rationale": "Good"}\n```'
+        decision = client.parse_response(raw)
+        assert decision.action == "BUY"
+        assert decision.confidence == 92
+
+
+# ---------------------------------------------------------------------------
+# Prompt Construction
+# ---------------------------------------------------------------------------
+
+
+class TestPromptConstruction:
+    """The prompt sent to Gemini must include all required market data."""
+
+    def test_prompt_contains_stock_code(self, settings):
+        client = GeminiClient(settings)
+        market_data = {
+            "stock_code": "005930",
+            "current_price": 72000,
+            "orderbook": {"asks": [], "bids": []},
+            "foreigner_net": -50000,
+        }
+        prompt = client.build_prompt(market_data)
+        assert "005930" in prompt
+
+    def test_prompt_contains_price(self, settings):
+        client = GeminiClient(settings)
+        market_data = {
+            "stock_code": "005930",
+            "current_price": 72000,
+            "orderbook": {"asks": [], "bids": []},
+            "foreigner_net": -50000,
+        }
+        prompt = client.build_prompt(market_data)
+        assert "72000" in prompt
+
+    def test_prompt_enforces_json_output_format(self, settings):
+        client = GeminiClient(settings)
+        market_data = {
+            "stock_code": "005930",
+            "current_price": 72000,
+            "orderbook": {"asks": [], "bids": []},
+            "foreigner_net": 0,
+        }
+        prompt = client.build_prompt(market_data)
+        assert "JSON" in prompt
+        assert "action" in prompt
+        assert "confidence" in prompt