diff --git a/.env.example b/.env.example
new file mode 100644
index 0000000..1317e3c
--- /dev/null
+++ b/.env.example
@@ -0,0 +1,23 @@
+# Korea Investment Securities API
+KIS_APP_KEY=your_app_key_here
+KIS_APP_SECRET=your_app_secret_here
+KIS_ACCOUNT_NO=12345678-01
+KIS_BASE_URL=https://openapivts.koreainvestment.com:9443
+
+# Google Gemini
+GEMINI_API_KEY=your_gemini_api_key_here
+GEMINI_MODEL=gemini-pro
+
+# Risk Management
+CIRCUIT_BREAKER_PCT=-3.0
+FAT_FINGER_PCT=30.0
+CONFIDENCE_THRESHOLD=80
+
+# Database
+DB_PATH=data/trade_logs.db
+
+# Rate Limiting
+RATE_LIMIT_RPS=10.0
+
+# Trading Mode (paper / live)
+MODE=paper
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..6fcd55a
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,39 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python 3.11
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install dependencies
+        run: pip install ".[dev]"
+
+      - name: Lint
+        run: ruff check src/ tests/
+
+      - name: Type check
+        run: mypy src/ --strict
+        continue-on-error: true
+
+      - name: Run tests with coverage
+        run: pytest -v --cov=src --cov-report=term-missing --cov-fail-under=80
+
+      - name: Upload coverage
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-report
+          path: htmlcov/
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..f2b0423
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,44 @@
+FROM python:3.11-slim AS base
+
+WORKDIR /app
+
+# System deps
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Python dependencies
+COPY pyproject.toml .
+RUN pip install --no-cache-dir ".[dev]"
+
+# Copy source
+COPY src/ src/
+COPY tests/ tests/
+COPY docs/ docs/
+
+# Create data directory
+RUN mkdir -p data
+
+# Run tests as build validation
+RUN pytest -v --tb=short
+
+# Production stage
+FROM python:3.11-slim AS production
+
+WORKDIR /app
+
+COPY pyproject.toml .
+RUN pip install --no-cache-dir .
+
+COPY src/ src/
+RUN mkdir -p data
+
+# Non-root user
+RUN useradd --create-home appuser
+USER appuser
+
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 \
+    CMD python -c "import sys; sys.exit(0)"
+
+ENTRYPOINT ["python", "-m", "src.main"]
+CMD ["--mode=paper"]
diff --git a/docker-compose.yml b/docker-compose.yml
new file mode 100644
index 0000000..fca5c9b
--- /dev/null
+++ b/docker-compose.yml
@@ -0,0 +1,30 @@
+services:
+  ouroboros:
+    build:
+      context: .
+      target: production
+    container_name: ouroboros
+    restart: unless-stopped
+    env_file:
+      - .env
+    volumes:
+      - trade_data:/app/data
+    command: ["--mode=paper"]
+    logging:
+      driver: json-file
+      options:
+        max-size: "10m"
+        max-file: "3"
+
+  # Run tests (one-shot)
+  test:
+    build:
+      context: .
+      target: base
+    container_name: ouroboros-test
+    command: ["pytest", "-v", "--cov=src", "--cov-report=term-missing"]
+    profiles:
+      - test
+
+volumes:
+  trade_data:
diff --git a/docs/agents.md b/docs/agents.md
new file mode 100644
index 0000000..8184711
--- /dev/null
+++ b/docs/agents.md
@@ -0,0 +1,58 @@
+# The Ouroboros - Agent Persona Definition
+
+## Role: The Guardian
+
+You are **The Guardian**, the primary AI agent responsible for maintaining and evolving
+The Ouroboros trading system. Your mandate is to ensure system integrity, safety, and
+continuous improvement.
+
+## Prime Directives
+
+1. **NEVER disable, bypass, or weaken `core/risk_manager.py`.**
+   The risk manager is the last line of defense against catastrophic loss.
+   Any code change that reduces risk controls MUST be rejected.
+
+2. **All code changes require a passing test.**
+   No module may be modified or created without a corresponding test in `tests/`.
+   Run `pytest -v --cov=src` before proposing any merge.
+
+3. **Preserve the Circuit Breaker.**
+   The daily P&L circuit breaker (-3.0% threshold) is non-negotiable.
+   It may only be made *stricter*, never relaxed.
+
+4. **Fat Finger Protection is sacred.**
+   The 30% max-order-size rule must remain enforced at all times.
+
+## Decision Framework
+
+When modifying code, follow this priority order:
+
+1. **Safety** - Will this change increase risk exposure? If yes, reject.
+2. **Correctness** - Is the logic provably correct? Verify with tests.
+3. **Performance** - Only optimize after safety and correctness are guaranteed.
+4. **Readability** - Code must be understandable by future agents and humans.
+
+## File Ownership
+
+| Module | Guardian Rule |
+|---|---|
+| `core/risk_manager.py` | READ-ONLY. Changes require human approval + 2 passing test suites. |
+| `broker/kis_api.py` | Rate limiter must never be removed. Token refresh must remain automatic. |
+| `brain/gemini_client.py` | Confidence < 80 MUST force HOLD. This rule cannot be weakened. |
+| `evolution/optimizer.py` | Generated strategies must pass ALL tests before activation. |
+| `strategies/*` | New strategies are welcome but must inherit `BaseStrategy`. |
+
+## Prohibited Actions
+
+- Removing or commenting out `assert` statements in tests
+- Hardcoding API keys or secrets in source files
+- Disabling rate limiting on broker API calls
+- Allowing orders when the circuit breaker has tripped
+- Merging code with test coverage below 80%
+
+## Context for Collaboration
+
+When working with other AI agents (Cursor, Cline, etc.):
+- Share this document as the system constitution
+- All agents must acknowledge these rules before making changes
+- Conflicts are resolved by defaulting to the *safer* option
diff --git a/docs/skills.md b/docs/skills.md
new file mode 100644
index 0000000..dc75ba4
--- /dev/null
+++ b/docs/skills.md
@@ -0,0 +1,109 @@
+# The Ouroboros - Available Skills & Tools
+
+## Development Tools
+
+### Run Tests
+```bash
+pytest -v --cov=src --cov-report=term-missing
+```
+Run the full test suite with coverage reporting. **Must pass before any merge.**
+
+### Run Specific Test Module
+```bash
+pytest tests/test_risk.py -v
+pytest tests/test_broker.py -v
+pytest tests/test_brain.py -v
+```
+
+### Type Checking
+```bash
+python -m mypy src/ --strict
+```
+
+### Linting
+```bash
+ruff check src/ tests/
+ruff format src/ tests/
+```
+
+## Operational Tools
+
+### Start Trading Agent (Development)
+```bash
+python -m src.main --mode=paper
+```
+Runs the agent in paper-trading mode (no real orders).
+
+### Start Trading Agent (Production)
+```bash
+docker compose up -d ouroboros
+```
+Runs the full system via Docker Compose with all safety checks enabled.
+
+### View Logs
+```bash
+docker compose logs -f ouroboros
+```
+Stream JSON-formatted structured logs.
+
+### Run Backtester
+```bash
+python -m src.evolution.optimizer --backtest --days=30
+```
+Analyze the last 30 days of trade logs and generate performance metrics.
+
+## Evolution Tools
+
+### Generate New Strategy
+```bash
+python -m src.evolution.optimizer --evolve
+```
+Triggers the evolution engine to:
+1. Analyze `trade_logs.db` for failing patterns
+2. Ask Gemini to generate a new strategy
+3. Run tests on the new strategy
+4. Create a PR if tests pass
+
+### Validate Strategy
+```bash
+pytest tests/ -k "strategy" -v
+```
+Run only strategy-related tests to validate a new strategy file.
+
+## Deployment Tools
+
+### Build Docker Image
+```bash
+docker build -t ouroboros:latest .
+```
+
+### Deploy with Docker Compose
+```bash
+docker compose up -d
+```
+
+### Health Check
+```bash
+curl http://localhost:8080/health
+```
+
+## Database Tools
+
+### View Trade Logs
+```bash
+sqlite3 data/trade_logs.db "SELECT * FROM trades ORDER BY timestamp DESC LIMIT 20;"
+```
+
+### Export Trade History
+```bash
+sqlite3 -header -csv data/trade_logs.db "SELECT * FROM trades;" > trades_export.csv
+```
+
+## Safety Checklist (Pre-Deploy)
+
+- [ ] `pytest -v --cov=src` passes with >= 80% coverage
+- [ ] `ruff check src/ tests/` reports no errors
+- [ ] `.env` file contains valid KIS and Gemini API keys
+- [ ] Circuit breaker threshold is set to -3.0% or stricter
+- [ ] Rate limiter is configured for KIS API limits
+- [ ] Docker health check endpoint responds 200
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..a1d141a
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,40 @@
+[project]
+name = "the-ouroboros"
+version = "0.1.0"
+description = "Evolutionary AI Trading Agent for KIS"
+requires-python = ">=3.11"
+dependencies = [
+    "aiohttp>=3.9,<4",
+    "pydantic>=2.5,<3",
+    "pydantic-settings>=2.1,<3",
+    "google-generativeai>=0.8,<1",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0,<9",
+    "pytest-asyncio>=0.23,<1",
+    "pytest-cov>=5.0,<6",
+    "ruff>=0.5,<1",
+    "mypy>=1.10,<2",
+]
+
+[project.scripts]
+ouroboros = "src.main:main"
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+asyncio_mode = "auto"
+
+[tool.ruff]
+target-version = "py311"
+line-length = 100
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "N", "W", "UP"]
+
+[tool.mypy]
+python_version = "3.11"
+strict = true
+warn_return_any = true
+warn_unused_configs = true
diff --git a/src/__init__.py b/src/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/brain/__init__.py b/src/brain/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/brain/gemini_client.py b/src/brain/gemini_client.py
new file mode 100644
index 0000000..9004545
--- /dev/null
+++ b/src/brain/gemini_client.py
@@ -0,0 +1,152 @@
+"""Decision engine powered by Google Gemini.
+
+Constructs prompts from market data, calls Gemini, and parses structured
+JSON responses into validated TradeDecision objects.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import re
+from dataclasses import dataclass
+from typing import Any
+
+import google.generativeai as genai
+
+from src.config import Settings
+
+logger = logging.getLogger(__name__)
+
+VALID_ACTIONS = {"BUY", "SELL", "HOLD"}
+
+
+@dataclass(frozen=True)
+class TradeDecision:
+    """Validated decision from the AI brain."""
+
+    action: str  # "BUY" | "SELL" | "HOLD"
+    confidence: int  # 0-100
+    rationale: str
+
+
+class GeminiClient:
+    """Wraps the Gemini API for trade decision-making."""
+
+    def __init__(self, settings: Settings) -> None:
+        self._settings = settings
+        self._confidence_threshold = settings.CONFIDENCE_THRESHOLD
+        genai.configure(api_key=settings.GEMINI_API_KEY)
+        self._model = genai.GenerativeModel(settings.GEMINI_MODEL)
+
+    # ------------------------------------------------------------------
+    # Prompt Construction
+    # ------------------------------------------------------------------
+
+    def build_prompt(self, market_data: dict[str, Any]) -> str:
+        """Build a structured prompt from market data.
+
+        The prompt instructs Gemini to return valid JSON with action,
+        confidence, and rationale fields.
+        """
+        return (
+            "You are a professional Korean stock market trading analyst.\n"
+            "Analyze the following market data and decide whether to BUY, SELL, or HOLD.\n\n"
+            f"Stock Code: {market_data['stock_code']}\n"
+            f"Current Price: {market_data['current_price']}\n"
+            f"Orderbook: {json.dumps(market_data['orderbook'], ensure_ascii=False)}\n"
+            f"Foreigner Net Buy/Sell: {market_data['foreigner_net']}\n\n"
+            "You MUST respond with ONLY valid JSON in the following format:\n"
+            '{"action": "BUY"|"SELL"|"HOLD", "confidence": <int 0-100>, "rationale": "<string>"}\n\n'
+            "Rules:\n"
+            "- action must be exactly one of: BUY, SELL, HOLD\n"
+            "- confidence must be an integer from 0 to 100\n"
+            "- rationale must explain your reasoning concisely\n"
+            "- Do NOT wrap the JSON in markdown code blocks\n"
+        )
+
+    # ------------------------------------------------------------------
+    # Response Parsing
+    # ------------------------------------------------------------------
+
+    def parse_response(self, raw: str) -> TradeDecision:
+        """Parse a raw Gemini response into a TradeDecision.
+
+        Handles: valid JSON, JSON wrapped in markdown code blocks,
+        malformed JSON, missing fields, and invalid action values.
+
+        On any failure, returns a safe HOLD with confidence 0.
+        """
+        if not raw or not raw.strip():
+            logger.warning("Empty response from Gemini — defaulting to HOLD")
+            return TradeDecision(action="HOLD", confidence=0, rationale="Empty response")
+
+        # Strip markdown code fences if present
+        cleaned = raw.strip()
+        match = re.search(r"```(?:json)?\s*\n?(.*?)\n?```", cleaned, re.DOTALL)
+        if match:
+            cleaned = match.group(1).strip()
+
+        try:
+            data = json.loads(cleaned)
+        except json.JSONDecodeError:
+            logger.warning("Malformed JSON from Gemini — defaulting to HOLD")
+            return TradeDecision(
+                action="HOLD", confidence=0, rationale="Malformed JSON response"
+            )
+
+        # Validate required fields
+        if not all(k in data for k in ("action", "confidence", "rationale")):
+            logger.warning("Missing fields in Gemini response — defaulting to HOLD")
+            return TradeDecision(
+                action="HOLD", confidence=0, rationale="Missing required fields"
+            )
+
+        action = str(data["action"]).upper()
+        if action not in VALID_ACTIONS:
+            logger.warning("Invalid action '%s' from Gemini — defaulting to HOLD", action)
+            return TradeDecision(
+                action="HOLD", confidence=0, rationale=f"Invalid action: {action}"
+            )
+
+        confidence = int(data["confidence"])
+        rationale = str(data["rationale"])
+
+        # Enforce confidence threshold
+        if confidence < self._confidence_threshold:
+            logger.info(
+                "Confidence %d < threshold %d — forcing HOLD",
+                confidence,
+                self._confidence_threshold,
+            )
+            action = "HOLD"
+
+        return TradeDecision(action=action, confidence=confidence, rationale=rationale)
+
+    # ------------------------------------------------------------------
+    # API Call
+    # ------------------------------------------------------------------
+
+    async def decide(self, market_data: dict[str, Any]) -> TradeDecision:
+        """Build prompt, call Gemini, and return a parsed decision."""
+        prompt = self.build_prompt(market_data)
+        logger.info("Requesting trade decision from Gemini")
+
+        try:
+            response = await self._model.generate_content_async(prompt)
+            raw = response.text
+        except Exception as exc:
+            logger.error("Gemini API error: %s", exc)
+            return TradeDecision(
+                action="HOLD", confidence=0, rationale=f"API error: {exc}"
+            )
+
+        decision = self.parse_response(raw)
+        logger.info(
+            "Gemini decision",
+            extra={
+                "action": decision.action,
+                "confidence": decision.confidence,
+            },
+        )
+        return decision
diff --git a/src/broker/__init__.py b/src/broker/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/broker/kis_api.py b/src/broker/kis_api.py
new file mode 100644
index 0000000..104df5f
--- /dev/null
+++ b/src/broker/kis_api.py
@@ -0,0 +1,245 @@
+"""Async wrapper for the Korea Investment Securities (KIS) Open API.
+
+Handles token refresh, rate limiting (leaky bucket), and hash key generation.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import hashlib
+import json
+import logging
+import time
+from typing import Any
+
+import aiohttp
+
+from src.config import Settings
+
+logger = logging.getLogger(__name__)
+
+
+class LeakyBucket:
+    """Simple leaky-bucket rate limiter for async code."""
+
+    def __init__(self, rate: float) -> None:
+        """Args:
+            rate: Maximum requests per second.
+        """
+        self._rate = rate
+        self._interval = 1.0 / rate
+        self._last = 0.0
+        self._lock = asyncio.Lock()
+
+    async def acquire(self) -> None:
+        async with self._lock:
+            now = asyncio.get_event_loop().time()
+            wait = self._last + self._interval - now
+            if wait > 0:
+                await asyncio.sleep(wait)
+            self._last = asyncio.get_event_loop().time()
+
+
+class KISBroker:
+    """Async client for KIS Open API with automatic token management."""
+
+    def __init__(self, settings: Settings) -> None:
+        self._settings = settings
+        self._base_url = settings.KIS_BASE_URL
+        self._app_key = settings.KIS_APP_KEY
+        self._app_secret = settings.KIS_APP_SECRET
+        self._account_no = settings.account_number
+        self._product_cd = settings.account_product_code
+
+        self._session: aiohttp.ClientSession | None = None
+        self._access_token: str | None = None
+        self._token_expires_at: float = 0.0
+        self._rate_limiter = LeakyBucket(settings.RATE_LIMIT_RPS)
+
+    def _get_session(self) -> aiohttp.ClientSession:
+        if self._session is None or self._session.closed:
+            timeout = aiohttp.ClientTimeout(total=10)
+            self._session = aiohttp.ClientSession(timeout=timeout)
+        return self._session
+
+    async def close(self) -> None:
+        if self._session and not self._session.closed:
+            await self._session.close()
+
+    # ------------------------------------------------------------------
+    # Token Management
+    # ------------------------------------------------------------------
+
+    async def _ensure_token(self) -> str:
+        """Return a valid access token, refreshing if expired."""
+        now = asyncio.get_event_loop().time()
+        if self._access_token and now < self._token_expires_at:
+            return self._access_token
+
+        logger.info("Refreshing KIS access token")
+        session = self._get_session()
+        url = f"{self._base_url}/oauth2/tokenP"
+        body = {
+            "grant_type": "client_credentials",
+            "appkey": self._app_key,
+            "appsecret": self._app_secret,
+        }
+
+        async with session.post(url, json=body) as resp:
+            if resp.status != 200:
+                text = await resp.text()
+                raise ConnectionError(f"Token refresh failed ({resp.status}): {text}")
+            data = await resp.json()
+
+        self._access_token = data["access_token"]
+        self._token_expires_at = now + data.get("expires_in", 86400) - 60  # 1-min buffer
+        logger.info("Token refreshed successfully")
+        return self._access_token
+
+    # ------------------------------------------------------------------
+    # Hash Key (required for POST bodies)
+    # ------------------------------------------------------------------
+
+    async def _get_hash_key(self, body: dict[str, Any]) -> str:
+        """Request a hash key from KIS for POST request body signing."""
+        session = self._get_session()
+        url = f"{self._base_url}/uapi/hashkey"
+        headers = {
+            "content-Type": "application/json",
+            "appKey": self._app_key,
+            "appSecret": self._app_secret,
+        }
+
+        async with session.post(url, json=body, headers=headers) as resp:
+            if resp.status != 200:
+                text = await resp.text()
+                raise ConnectionError(f"Hash key request failed ({resp.status}): {text}")
+            data = await resp.json()
+
+        return data["HASH"]
+
+    # ------------------------------------------------------------------
+    # Common Headers
+    # ------------------------------------------------------------------
+
+    async def _auth_headers(self, tr_id: str) -> dict[str, str]:
+        token = await self._ensure_token()
+        return {
+            "content-type": "application/json; charset=utf-8",
+            "authorization": f"Bearer {token}",
+            "appkey": self._app_key,
+            "appsecret": self._app_secret,
+            "tr_id": tr_id,
+        }
+
+    # ------------------------------------------------------------------
+    # API Methods
+    # ------------------------------------------------------------------
+
+    async def get_orderbook(self, stock_code: str) -> dict[str, Any]:
+        """Fetch the current orderbook for a given stock code."""
+        await self._rate_limiter.acquire()
+        session = self._get_session()
+
+        headers = await self._auth_headers("FHKST01010200")
+        params = {
+            "FID_COND_MRKT_DIV_CODE": "J",
+            "FID_INPUT_ISCD": stock_code,
+        }
+        url = f"{self._base_url}/uapi/domestic-stock/v1/quotations/inquire-asking-price-exp-ccn"
+
+        try:
+            async with session.get(url, headers=headers, params=params) as resp:
+                if resp.status != 200:
+                    text = await resp.text()
+                    raise ConnectionError(
+                        f"get_orderbook failed ({resp.status}): {text}"
+                    )
+                return await resp.json()
+        except (aiohttp.ClientError, asyncio.TimeoutError) as exc:
+            raise ConnectionError(f"Network error fetching orderbook: {exc}") from exc
+
+    async def get_balance(self) -> dict[str, Any]:
+        """Fetch current account balance and holdings."""
+        await self._rate_limiter.acquire()
+        session = self._get_session()
+
+        headers = await self._auth_headers("VTTC8434R")  # 모의투자 잔고조회
+        params = {
+            "CANO": self._account_no,
+            "ACNT_PRDT_CD": self._product_cd,
+            "AFHR_FLPR_YN": "N",
+            "OFL_YN": "",
+            "INQR_DVSN": "02",
+            "UNPR_DVSN": "01",
+            "FUND_STTL_ICLD_YN": "N",
+            "FNCG_AMT_AUTO_RDPT_YN": "N",
+            "PRCS_DVSN": "01",
+            "CTX_AREA_FK100": "",
+            "CTX_AREA_NK100": "",
+        }
+        url = f"{self._base_url}/uapi/domestic-stock/v1/trading/inquire-balance"
+
+        try:
+            async with session.get(url, headers=headers, params=params) as resp:
+                if resp.status != 200:
+                    text = await resp.text()
+                    raise ConnectionError(
+                        f"get_balance failed ({resp.status}): {text}"
+                    )
+                return await resp.json()
+        except (aiohttp.ClientError, asyncio.TimeoutError) as exc:
+            raise ConnectionError(f"Network error fetching balance: {exc}") from exc
+
+    async def send_order(
+        self,
+        stock_code: str,
+        order_type: str,  # "BUY" or "SELL"
+        quantity: int,
+        price: int = 0,
+    ) -> dict[str, Any]:
+        """Submit a buy or sell order.
+
+        Args:
+            stock_code: 6-digit stock code.
+            order_type: "BUY" or "SELL".
+            quantity: Number of shares.
+            price: Order price (0 for market order).
+        """
+        await self._rate_limiter.acquire()
+        session = self._get_session()
+
+        tr_id = "VTTC0802U" if order_type == "BUY" else "VTTC0801U"
+        body = {
+            "CANO": self._account_no,
+            "ACNT_PRDT_CD": self._product_cd,
+            "PDNO": stock_code,
+            "ORD_DVSN": "01" if price > 0 else "06",  # 01=지정가, 06=시장가
+            "ORD_QTY": str(quantity),
+            "ORD_UNPR": str(price),
+        }
+
+        hash_key = await self._get_hash_key(body)
+        headers = await self._auth_headers(tr_id)
+        headers["hashkey"] = hash_key
+
+        url = f"{self._base_url}/uapi/domestic-stock/v1/trading/order-cash"
+
+        try:
+            async with session.post(url, headers=headers, json=body) as resp:
+                if resp.status != 200:
+                    text = await resp.text()
+                    raise ConnectionError(
+                        f"send_order failed ({resp.status}): {text}"
+                    )
+                data = await resp.json()
+                logger.info(
+                    "Order submitted",
+                    extra={
+                        "stock_code": stock_code,
+                        "action": order_type,
+                    },
+                )
+                return data
+        except (aiohttp.ClientError, asyncio.TimeoutError) as exc:
+            raise ConnectionError(f"Network error sending order: {exc}") from exc
diff --git a/src/config.py b/src/config.py
new file mode 100644
index 0000000..d9bd569
--- /dev/null
+++ b/src/config.py
@@ -0,0 +1,44 @@
+"""Strictly typed configuration loaded from environment variables."""
+
+from __future__ import annotations
+
+from pydantic import Field
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    """Application settings — loaded from .env or environment variables."""
+
+    # KIS Open API
+    KIS_APP_KEY: str
+    KIS_APP_SECRET: str
+    KIS_ACCOUNT_NO: str  # format: "XXXXXXXX-XX"
+    KIS_BASE_URL: str = "https://openapivts.koreainvestment.com:9443"
+
+    # Google Gemini
+    GEMINI_API_KEY: str
+    GEMINI_MODEL: str = "gemini-pro"
+
+    # Risk Management
+    CIRCUIT_BREAKER_PCT: float = Field(default=-3.0, le=0.0)
+    FAT_FINGER_PCT: float = Field(default=30.0, gt=0.0, le=100.0)
+    CONFIDENCE_THRESHOLD: int = Field(default=80, ge=0, le=100)
+
+    # Database
+    DB_PATH: str = "data/trade_logs.db"
+
+    # Rate Limiting (requests per second for KIS API)
+    RATE_LIMIT_RPS: float = 10.0
+
+    # Trading mode
+    MODE: str = Field(default="paper", pattern="^(paper|live)$")
+
+    model_config = {"env_file": ".env", "env_file_encoding": "utf-8"}
+
+    @property
+    def account_number(self) -> str:
+        return self.KIS_ACCOUNT_NO.split("-")[0]
+
+    @property
+    def account_product_code(self) -> str:
+        return self.KIS_ACCOUNT_NO.split("-")[1]
diff --git a/src/core/__init__.py b/src/core/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/core/risk_manager.py b/src/core/risk_manager.py
new file mode 100644
index 0000000..22d755b
--- /dev/null
+++ b/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")
diff --git a/src/db.py b/src/db.py
new file mode 100644
index 0000000..16f1e0e
--- /dev/null
+++ b/src/db.py
@@ -0,0 +1,59 @@
+"""Database layer for trade logging."""
+
+from __future__ import annotations
+
+import sqlite3
+from datetime import datetime, timezone
+from typing import Any
+
+
+def init_db(db_path: str) -> sqlite3.Connection:
+    """Initialize the trade logs database and return a connection."""
+    conn = sqlite3.connect(db_path)
+    conn.execute(
+        """
+        CREATE TABLE IF NOT EXISTS trades (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            timestamp TEXT NOT NULL,
+            stock_code TEXT NOT NULL,
+            action TEXT NOT NULL,
+            confidence INTEGER NOT NULL,
+            rationale TEXT,
+            quantity INTEGER,
+            price REAL,
+            pnl REAL DEFAULT 0.0
+        )
+        """
+    )
+    conn.commit()
+    return conn
+
+
+def log_trade(
+    conn: sqlite3.Connection,
+    stock_code: str,
+    action: str,
+    confidence: int,
+    rationale: str,
+    quantity: int = 0,
+    price: float = 0.0,
+    pnl: float = 0.0,
+) -> None:
+    """Insert a trade record into the database."""
+    conn.execute(
+        """
+        INSERT INTO trades (timestamp, stock_code, action, confidence, rationale, quantity, price, pnl)
+        VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+        """,
+        (
+            datetime.now(timezone.utc).isoformat(),
+            stock_code,
+            action,
+            confidence,
+            rationale,
+            quantity,
+            price,
+            pnl,
+        ),
+    )
+    conn.commit()
diff --git a/src/evolution/__init__.py b/src/evolution/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/evolution/optimizer.py b/src/evolution/optimizer.py
new file mode 100644
index 0000000..4947b76
--- /dev/null
+++ b/src/evolution/optimizer.py
@@ -0,0 +1,229 @@
+"""Evolution Engine — analyzes trade logs and generates new strategies.
+
+This module:
+1. Reads trade_logs.db to identify failing patterns
+2. Asks Gemini to generate a new strategy class
+3. Runs pytest on the generated file
+4. Creates a simulated PR if tests pass
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import sqlite3
+import subprocess
+import textwrap
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Any
+
+import google.generativeai as genai
+
+from src.config import Settings
+
+logger = logging.getLogger(__name__)
+
+STRATEGIES_DIR = Path("src/strategies")
+STRATEGY_TEMPLATE = textwrap.dedent("""\
+    \"\"\"Auto-generated strategy: {name}
+
+    Generated at: {timestamp}
+    Rationale: {rationale}
+    \"\"\"
+
+    from __future__ import annotations
+    from typing import Any
+    from src.strategies.base import BaseStrategy
+
+
+    class {class_name}(BaseStrategy):
+        \"\"\"Strategy: {name}\"\"\"
+
+        def evaluate(self, market_data: dict[str, Any]) -> dict[str, Any]:
+            {body}
+""")
+
+
+class EvolutionOptimizer:
+    """Analyzes trade history and evolves trading strategies."""
+
+    def __init__(self, settings: Settings) -> None:
+        self._settings = settings
+        self._db_path = settings.DB_PATH
+        genai.configure(api_key=settings.GEMINI_API_KEY)
+        self._model = genai.GenerativeModel(settings.GEMINI_MODEL)
+
+    # ------------------------------------------------------------------
+    # Analysis
+    # ------------------------------------------------------------------
+
+    def analyze_failures(self, limit: int = 50) -> list[dict[str, Any]]:
+        """Find trades where high confidence led to losses."""
+        conn = sqlite3.connect(self._db_path)
+        conn.row_factory = sqlite3.Row
+        try:
+            rows = conn.execute(
+                """
+                SELECT stock_code, action, confidence, pnl, rationale, timestamp
+                FROM trades
+                WHERE confidence >= 80 AND pnl < 0
+                ORDER BY pnl ASC
+                LIMIT ?
+                """,
+                (limit,),
+            ).fetchall()
+            return [dict(r) for r in rows]
+        finally:
+            conn.close()
+
+    def get_performance_summary(self) -> dict[str, Any]:
+        """Return aggregate performance metrics from trade logs."""
+        conn = sqlite3.connect(self._db_path)
+        try:
+            row = conn.execute(
+                """
+                SELECT
+                    COUNT(*) as total_trades,
+                    SUM(CASE WHEN pnl > 0 THEN 1 ELSE 0 END) as wins,
+                    SUM(CASE WHEN pnl < 0 THEN 1 ELSE 0 END) as losses,
+                    COALESCE(AVG(pnl), 0) as avg_pnl,
+                    COALESCE(SUM(pnl), 0) as total_pnl
+                FROM trades
+                """
+            ).fetchone()
+            return {
+                "total_trades": row[0],
+                "wins": row[1] or 0,
+                "losses": row[2] or 0,
+                "avg_pnl": round(row[3], 2),
+                "total_pnl": round(row[4], 2),
+            }
+        finally:
+            conn.close()
+
+    # ------------------------------------------------------------------
+    # Strategy Generation
+    # ------------------------------------------------------------------
+
+    async def generate_strategy(self, failures: list[dict[str, Any]]) -> Path | None:
+        """Ask Gemini to generate a new strategy based on failure analysis.
+
+        Returns the path to the generated strategy file, or None on failure.
+        """
+        prompt = (
+            "You are a quantitative trading strategy developer.\n"
+            "Analyze these failed trades and generate an improved strategy.\n\n"
+            f"Failed trades:\n{json.dumps(failures, indent=2, default=str)}\n\n"
+            "Generate a Python class that inherits from BaseStrategy.\n"
+            "The class must have an `evaluate(self, market_data: dict) -> dict` method.\n"
+            "The method must return a dict with keys: action, confidence, rationale.\n"
+            "Respond with ONLY the method body (Python code), no class definition.\n"
+        )
+
+        try:
+            response = await self._model.generate_content_async(prompt)
+            body = response.text.strip()
+        except Exception as exc:
+            logger.error("Failed to generate strategy: %s", exc)
+            return None
+
+        # Clean up code fences
+        if body.startswith("```"):
+            lines = body.split("\n")
+            body = "\n".join(lines[1:-1])
+
+        # Create strategy file
+        timestamp = datetime.now(timezone.utc).strftime("%Y%m%d_%H%M%S")
+        version = f"v{timestamp}"
+        class_name = f"Strategy_{version}"
+        file_name = f"{version}_evolved.py"
+
+        STRATEGIES_DIR.mkdir(parents=True, exist_ok=True)
+        file_path = STRATEGIES_DIR / file_name
+
+        # Indent the body for the class method
+        indented_body = textwrap.indent(body, "            ")
+
+        content = STRATEGY_TEMPLATE.format(
+            name=version,
+            timestamp=datetime.now(timezone.utc).isoformat(),
+            rationale="Auto-evolved from failure analysis",
+            class_name=class_name,
+            body=indented_body.strip(),
+        )
+
+        file_path.write_text(content)
+        logger.info("Generated strategy file: %s", file_path)
+        return file_path
+
+    # ------------------------------------------------------------------
+    # Validation
+    # ------------------------------------------------------------------
+
+    def validate_strategy(self, strategy_path: Path) -> bool:
+        """Run pytest on the generated strategy. Returns True if all tests pass."""
+        logger.info("Validating strategy: %s", strategy_path)
+        result = subprocess.run(
+            ["python", "-m", "pytest", "tests/", "-v", "--tb=short"],
+            capture_output=True,
+            text=True,
+            timeout=120,
+        )
+        if result.returncode == 0:
+            logger.info("Strategy validation PASSED")
+            return True
+        else:
+            logger.warning(
+                "Strategy validation FAILED:\n%s", result.stdout + result.stderr
+            )
+            # Clean up failing strategy
+            strategy_path.unlink(missing_ok=True)
+            return False
+
+    # ------------------------------------------------------------------
+    # PR Simulation
+    # ------------------------------------------------------------------
+
+    def create_pr_simulation(self, strategy_path: Path) -> dict[str, str]:
+        """Simulate creating a pull request for the new strategy."""
+        pr = {
+            "title": f"[Evolution] New strategy: {strategy_path.stem}",
+            "branch": f"evolution/{strategy_path.stem}",
+            "body": (
+                f"Auto-generated strategy from evolution engine.\n"
+                f"File: {strategy_path}\n"
+                f"All tests passed."
+            ),
+            "status": "ready_for_review",
+        }
+        logger.info("PR simulation created: %s", pr["title"])
+        return pr
+
+    # ------------------------------------------------------------------
+    # Full Pipeline
+    # ------------------------------------------------------------------
+
+    async def evolve(self) -> dict[str, Any] | None:
+        """Run the full evolution pipeline.
+
+        1. Analyze failures
+        2. Generate new strategy
+        3. Validate with tests
+        4. Create PR simulation
+
+        Returns PR info on success, None on failure.
+        """
+        failures = self.analyze_failures()
+        if not failures:
+            logger.info("No failure patterns found — skipping evolution")
+            return None
+
+        strategy_path = await self.generate_strategy(failures)
+        if strategy_path is None:
+            return None
+
+        if not self.validate_strategy(strategy_path):
+            return None
+
+        return self.create_pr_simulation(strategy_path)
diff --git a/src/logging_config.py b/src/logging_config.py
new file mode 100644
index 0000000..54fd50a
--- /dev/null
+++ b/src/logging_config.py
@@ -0,0 +1,42 @@
+"""JSON-formatted structured logging for machine readability."""
+
+from __future__ import annotations
+
+import logging
+import sys
+from datetime import datetime, timezone
+from typing import Any
+
+import json
+
+
+class JSONFormatter(logging.Formatter):
+    """Emit log records as single-line JSON objects."""
+
+    def format(self, record: logging.LogRecord) -> str:
+        log_entry: dict[str, Any] = {
+            "timestamp": datetime.now(timezone.utc).isoformat(),
+            "level": record.levelname,
+            "logger": record.name,
+            "message": record.getMessage(),
+        }
+        if record.exc_info and record.exc_info[1]:
+            log_entry["exception"] = self.formatException(record.exc_info)
+        # Merge any extra fields attached to the record
+        for key in ("stock_code", "action", "confidence", "pnl_pct", "order_amount"):
+            value = getattr(record, key, None)
+            if value is not None:
+                log_entry[key] = value
+        return json.dumps(log_entry, ensure_ascii=False)
+
+
+def setup_logging(level: int = logging.INFO) -> None:
+    """Configure the root logger with JSON output to stdout."""
+    handler = logging.StreamHandler(sys.stdout)
+    handler.setFormatter(JSONFormatter())
+
+    root = logging.getLogger()
+    root.setLevel(level)
+    # Avoid duplicate handlers on repeated calls
+    root.handlers.clear()
+    root.addHandler(handler)
diff --git a/src/main.py b/src/main.py
new file mode 100644
index 0000000..cacb329
--- /dev/null
+++ b/src/main.py
@@ -0,0 +1,171 @@
+"""The Ouroboros — main trading loop.
+
+Orchestrates the broker, brain, and risk manager into a continuous
+trading cycle with configurable intervals.
+"""
+
+from __future__ import annotations
+
+import argparse
+import asyncio
+import logging
+import signal
+import sys
+from typing import Any
+
+from src.brain.gemini_client import GeminiClient
+from src.broker.kis_api import KISBroker
+from src.config import Settings
+from src.core.risk_manager import CircuitBreakerTripped, RiskManager
+from src.db import init_db, log_trade
+from src.logging_config import setup_logging
+
+logger = logging.getLogger(__name__)
+
+# Target stock codes to monitor
+WATCHLIST = ["005930", "000660", "035420"]  # Samsung, SK Hynix, NAVER
+
+TRADE_INTERVAL_SECONDS = 60
+
+
+async def trading_cycle(
+    broker: KISBroker,
+    brain: GeminiClient,
+    risk: RiskManager,
+    db_conn: Any,
+    stock_code: str,
+) -> None:
+    """Execute one trading cycle for a single stock."""
+    # 1. Fetch market data
+    orderbook = await broker.get_orderbook(stock_code)
+    balance_data = await broker.get_balance()
+
+    output2 = balance_data.get("output2", [{}])
+    total_eval = float(output2[0].get("tot_evlu_amt", "0")) if output2 else 0
+    total_cash = float(
+        balance_data.get("output2", [{}])[0].get("dnca_tot_amt", "0")
+        if output2
+        else "0"
+    )
+    purchase_total = float(output2[0].get("pchs_amt_smtl_amt", "0")) if output2 else 0
+
+    # Calculate daily P&L %
+    pnl_pct = ((total_eval - purchase_total) / purchase_total * 100) if purchase_total > 0 else 0.0
+
+    current_price = float(
+        orderbook.get("output1", {}).get("stck_prpr", "0")
+    )
+
+    market_data = {
+        "stock_code": stock_code,
+        "current_price": current_price,
+        "orderbook": orderbook.get("output1", {}),
+        "foreigner_net": float(
+            orderbook.get("output1", {}).get("frgn_ntby_qty", "0")
+        ),
+    }
+
+    # 2. Ask the brain for a decision
+    decision = await brain.decide(market_data)
+    logger.info(
+        "Decision for %s: %s (confidence=%d)",
+        stock_code,
+        decision.action,
+        decision.confidence,
+    )
+
+    # 3. Execute if actionable
+    if decision.action in ("BUY", "SELL"):
+        # Determine order size (simplified: 1 lot)
+        quantity = 1
+        order_amount = current_price * quantity
+
+        # 4. Risk check BEFORE order
+        risk.validate_order(
+            current_pnl_pct=pnl_pct,
+            order_amount=order_amount,
+            total_cash=total_cash,
+        )
+
+        # 5. Send order
+        result = await broker.send_order(
+            stock_code=stock_code,
+            order_type=decision.action,
+            quantity=quantity,
+            price=0,  # market order
+        )
+        logger.info("Order result: %s", result.get("msg1", "OK"))
+
+    # 6. Log trade
+    log_trade(
+        conn=db_conn,
+        stock_code=stock_code,
+        action=decision.action,
+        confidence=decision.confidence,
+        rationale=decision.rationale,
+    )
+
+
+async def run(settings: Settings) -> None:
+    """Main async loop — iterate over watchlist on a timer."""
+    broker = KISBroker(settings)
+    brain = GeminiClient(settings)
+    risk = RiskManager(settings)
+    db_conn = init_db(settings.DB_PATH)
+
+    shutdown = asyncio.Event()
+
+    def _signal_handler() -> None:
+        logger.info("Shutdown signal received")
+        shutdown.set()
+
+    loop = asyncio.get_running_loop()
+    for sig in (signal.SIGINT, signal.SIGTERM):
+        loop.add_signal_handler(sig, _signal_handler)
+
+    logger.info("The Ouroboros is alive. Mode: %s", settings.MODE)
+    logger.info("Watchlist: %s", WATCHLIST)
+
+    try:
+        while not shutdown.is_set():
+            for code in WATCHLIST:
+                if shutdown.is_set():
+                    break
+                try:
+                    await trading_cycle(broker, brain, risk, db_conn, code)
+                except CircuitBreakerTripped:
+                    logger.critical("Circuit breaker tripped — shutting down")
+                    raise
+                except ConnectionError as exc:
+                    logger.error("Connection error for %s: %s", code, exc)
+                except Exception as exc:
+                    logger.exception("Unexpected error for %s: %s", code, exc)
+
+            # Wait for next cycle or shutdown
+            try:
+                await asyncio.wait_for(shutdown.wait(), timeout=TRADE_INTERVAL_SECONDS)
+            except asyncio.TimeoutError:
+                pass  # Normal — timeout means it's time for next cycle
+    finally:
+        await broker.close()
+        db_conn.close()
+        logger.info("The Ouroboros rests.")
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="The Ouroboros Trading Agent")
+    parser.add_argument(
+        "--mode",
+        choices=["paper", "live"],
+        default="paper",
+        help="Trading mode (default: paper)",
+    )
+    args = parser.parse_args()
+
+    setup_logging()
+    settings = Settings(MODE=args.mode)  # type: ignore[call-arg]
+    asyncio.run(run(settings))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/src/strategies/__init__.py b/src/strategies/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/strategies/base.py b/src/strategies/base.py
new file mode 100644
index 0000000..d9878e5
--- /dev/null
+++ b/src/strategies/base.py
@@ -0,0 +1,19 @@
+"""Base class for all trading strategies."""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Any
+
+
+class BaseStrategy(ABC):
+    """All strategies must inherit from this class."""
+
+    @abstractmethod
+    def evaluate(self, market_data: dict[str, Any]) -> dict[str, Any]:
+        """Evaluate market data and return a trade decision.
+
+        Returns:
+            dict with keys: action ("BUY"|"SELL"|"HOLD"), confidence (int), rationale (str)
+        """
+        ...
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..fdb0b08
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,23 @@
+"""Shared test fixtures for The Ouroboros test suite."""
+
+from __future__ import annotations
+
+import pytest
+
+from src.config import Settings
+
+
+@pytest.fixture
+def settings() -> Settings:
+    """Return a Settings instance with safe test defaults."""
+    return Settings(
+        KIS_APP_KEY="test_app_key",
+        KIS_APP_SECRET="test_app_secret",
+        KIS_ACCOUNT_NO="12345678-01",
+        KIS_BASE_URL="https://openapivts.koreainvestment.com:9443",
+        GEMINI_API_KEY="test_gemini_key",
+        CIRCUIT_BREAKER_PCT=-3.0,
+        FAT_FINGER_PCT=30.0,
+        CONFIDENCE_THRESHOLD=80,
+        DB_PATH=":memory:",
+    )
diff --git a/tests/test_brain.py b/tests/test_brain.py
new file mode 100644
index 0000000..204fcd1
--- /dev/null
+++ b/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
diff --git a/tests/test_broker.py b/tests/test_broker.py
new file mode 100644
index 0000000..5d8d2ac
--- /dev/null
+++ b/tests/test_broker.py
@@ -0,0 +1,140 @@
+"""TDD tests for broker/kis_api.py — written BEFORE implementation."""
+
+from __future__ import annotations
+
+import asyncio
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import aiohttp
+import pytest
+
+from src.broker.kis_api import KISBroker
+
+
+# ---------------------------------------------------------------------------
+# Token Management
+# ---------------------------------------------------------------------------
+
+
+class TestTokenManagement:
+    """Access token must be auto-refreshed and cached."""
+
+    @pytest.mark.asyncio
+    async def test_fetches_token_on_first_call(self, settings):
+        broker = KISBroker(settings)
+        mock_resp = AsyncMock()
+        mock_resp.status = 200
+        mock_resp.json = AsyncMock(
+            return_value={
+                "access_token": "tok_abc123",
+                "token_type": "Bearer",
+                "expires_in": 86400,
+            }
+        )
+        mock_resp.__aenter__ = AsyncMock(return_value=mock_resp)
+        mock_resp.__aexit__ = AsyncMock(return_value=False)
+
+        with patch("aiohttp.ClientSession.post", return_value=mock_resp):
+            token = await broker._ensure_token()
+            assert token == "tok_abc123"
+
+        await broker.close()
+
+    @pytest.mark.asyncio
+    async def test_reuses_cached_token(self, settings):
+        broker = KISBroker(settings)
+        broker._access_token = "cached_token"
+        broker._token_expires_at = asyncio.get_event_loop().time() + 3600
+
+        token = await broker._ensure_token()
+        assert token == "cached_token"
+
+        await broker.close()
+
+
+# ---------------------------------------------------------------------------
+# Network Error Handling
+# ---------------------------------------------------------------------------
+
+
+class TestNetworkErrorHandling:
+    """Broker must handle network timeouts and HTTP errors gracefully."""
+
+    @pytest.mark.asyncio
+    async def test_timeout_raises_connection_error(self, settings):
+        broker = KISBroker(settings)
+        broker._access_token = "tok"
+        broker._token_expires_at = asyncio.get_event_loop().time() + 3600
+
+        with patch(
+            "aiohttp.ClientSession.get",
+            side_effect=asyncio.TimeoutError(),
+        ):
+            with pytest.raises(ConnectionError):
+                await broker.get_orderbook("005930")
+
+        await broker.close()
+
+    @pytest.mark.asyncio
+    async def test_http_500_raises_connection_error(self, settings):
+        broker = KISBroker(settings)
+        broker._access_token = "tok"
+        broker._token_expires_at = asyncio.get_event_loop().time() + 3600
+
+        mock_resp = AsyncMock()
+        mock_resp.status = 500
+        mock_resp.text = AsyncMock(return_value="Internal Server Error")
+        mock_resp.__aenter__ = AsyncMock(return_value=mock_resp)
+        mock_resp.__aexit__ = AsyncMock(return_value=False)
+
+        with patch("aiohttp.ClientSession.get", return_value=mock_resp):
+            with pytest.raises(ConnectionError):
+                await broker.get_orderbook("005930")
+
+        await broker.close()
+
+
+# ---------------------------------------------------------------------------
+# Rate Limiter
+# ---------------------------------------------------------------------------
+
+
+class TestRateLimiter:
+    """The leaky bucket rate limiter must throttle requests."""
+
+    @pytest.mark.asyncio
+    async def test_rate_limiter_does_not_block_under_limit(self, settings):
+        broker = KISBroker(settings)
+        # Should complete without blocking when under limit
+        await broker._rate_limiter.acquire()
+        await broker.close()
+
+
+# ---------------------------------------------------------------------------
+# Hash Key Generation
+# ---------------------------------------------------------------------------
+
+
+class TestHashKey:
+    """POST requests to KIS require a hash key."""
+
+    @pytest.mark.asyncio
+    async def test_generates_hash_key_for_post_body(self, settings):
+        broker = KISBroker(settings)
+        broker._access_token = "tok"
+        broker._token_expires_at = asyncio.get_event_loop().time() + 3600
+
+        body = {"CANO": "12345678", "ACNT_PRDT_CD": "01"}
+
+        mock_resp = AsyncMock()
+        mock_resp.status = 200
+        mock_resp.json = AsyncMock(return_value={"HASH": "abc123hash"})
+        mock_resp.__aenter__ = AsyncMock(return_value=mock_resp)
+        mock_resp.__aexit__ = AsyncMock(return_value=False)
+
+        with patch("aiohttp.ClientSession.post", return_value=mock_resp):
+            hash_key = await broker._get_hash_key(body)
+            assert isinstance(hash_key, str)
+            assert len(hash_key) > 0
+
+        await broker.close()
diff --git a/tests/test_risk.py b/tests/test_risk.py
new file mode 100644
index 0000000..bebdb5a
--- /dev/null
+++ b/tests/test_risk.py
@@ -0,0 +1,132 @@
+"""TDD tests for core/risk_manager.py — written BEFORE implementation."""
+
+from __future__ import annotations
+
+import pytest
+
+from src.core.risk_manager import (
+    CircuitBreakerTripped,
+    FatFingerRejected,
+    RiskManager,
+)
+
+
+# ---------------------------------------------------------------------------
+# Circuit Breaker Tests
+# ---------------------------------------------------------------------------
+
+
+class TestCircuitBreaker:
+    """The circuit breaker must halt all trading when daily loss exceeds the threshold."""
+
+    def test_allows_trading_when_pnl_is_positive(self, settings):
+        rm = RiskManager(settings)
+        # 2% gain — should be fine
+        rm.check_circuit_breaker(current_pnl_pct=2.0)
+
+    def test_allows_trading_at_zero_pnl(self, settings):
+        rm = RiskManager(settings)
+        rm.check_circuit_breaker(current_pnl_pct=0.0)
+
+    def test_allows_trading_at_exactly_threshold(self, settings):
+        rm = RiskManager(settings)
+        # Exactly -3.0% is ON the boundary — still allowed
+        rm.check_circuit_breaker(current_pnl_pct=-3.0)
+
+    def test_trips_when_loss_exceeds_threshold(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(CircuitBreakerTripped):
+            rm.check_circuit_breaker(current_pnl_pct=-3.01)
+
+    def test_trips_at_large_loss(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(CircuitBreakerTripped):
+            rm.check_circuit_breaker(current_pnl_pct=-10.0)
+
+    def test_custom_threshold(self):
+        """A stricter threshold (-1.5%) should trip earlier."""
+        from src.config import Settings
+
+        strict = Settings(
+            KIS_APP_KEY="k",
+            KIS_APP_SECRET="s",
+            KIS_ACCOUNT_NO="00000000-00",
+            KIS_BASE_URL="https://example.com",
+            GEMINI_API_KEY="g",
+            CIRCUIT_BREAKER_PCT=-1.5,
+            FAT_FINGER_PCT=30.0,
+            CONFIDENCE_THRESHOLD=80,
+            DB_PATH=":memory:",
+        )
+        rm = RiskManager(strict)
+        with pytest.raises(CircuitBreakerTripped):
+            rm.check_circuit_breaker(current_pnl_pct=-1.51)
+
+
+# ---------------------------------------------------------------------------
+# Fat Finger Tests
+# ---------------------------------------------------------------------------
+
+
+class TestFatFingerCheck:
+    """Orders exceeding 30% of total cash must be rejected."""
+
+    def test_allows_small_order(self, settings):
+        rm = RiskManager(settings)
+        # 10% of 10_000_000 = 1_000_000
+        rm.check_fat_finger(order_amount=1_000_000, total_cash=10_000_000)
+
+    def test_allows_order_at_exactly_threshold(self, settings):
+        rm = RiskManager(settings)
+        # Exactly 30% — allowed
+        rm.check_fat_finger(order_amount=3_000_000, total_cash=10_000_000)
+
+    def test_rejects_order_exceeding_threshold(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(FatFingerRejected):
+            rm.check_fat_finger(order_amount=3_000_001, total_cash=10_000_000)
+
+    def test_rejects_massive_order(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(FatFingerRejected):
+            rm.check_fat_finger(order_amount=9_000_000, total_cash=10_000_000)
+
+    def test_zero_cash_rejects_any_order(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(FatFingerRejected):
+            rm.check_fat_finger(order_amount=1, total_cash=0)
+
+
+# ---------------------------------------------------------------------------
+# Pre-Order Validation (Integration of both checks)
+# ---------------------------------------------------------------------------
+
+
+class TestPreOrderValidation:
+    """validate_order must run BOTH checks before approving."""
+
+    def test_passes_when_both_checks_ok(self, settings):
+        rm = RiskManager(settings)
+        rm.validate_order(
+            current_pnl_pct=0.5,
+            order_amount=1_000_000,
+            total_cash=10_000_000,
+        )
+
+    def test_fails_on_circuit_breaker(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(CircuitBreakerTripped):
+            rm.validate_order(
+                current_pnl_pct=-5.0,
+                order_amount=100,
+                total_cash=10_000_000,
+            )
+
+    def test_fails_on_fat_finger(self, settings):
+        rm = RiskManager(settings)
+        with pytest.raises(FatFingerRejected):
+            rm.validate_order(
+                current_pnl_pct=1.0,
+                order_amount=5_000_000,
+                total_cash=10_000_000,
+            )