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backend/db/pool.py

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+"""
+backend/db/pool.py — asyncpg Connection Pool
+
+Initialises a PostgreSQL connection pool from environment variables.
+All credentials are sourced from the environment only — never hardcoded.
+
+Environment variables required:
+  VELOCITY_DB_HOST      PostgreSQL host (default: localhost)
+  VELOCITY_DB_PORT      PostgreSQL port (default: 5432)
+  VELOCITY_DB_NAME      Database name
+  VELOCITY_DB_USER      Database user
+  VELOCITY_DB_PASSWORD  Database password (injected from AWS SSM at service start)
+"""
+
+from __future__ import annotations
+
+import os
+from contextlib import asynccontextmanager
+from typing import AsyncGenerator
+
+import asyncpg
+from fastapi import Request
+
+_pool: asyncpg.Pool | None = None
+
+
+async def create_pool() -> asyncpg.Pool:
+    """Creates and returns the application-wide asyncpg connection pool."""
+    global _pool
+    _pool = await asyncpg.create_pool(
+        host=os.environ.get("VELOCITY_DB_HOST", "localhost"),
+        port=int(os.environ.get("VELOCITY_DB_PORT", "5432")),
+        database=os.environ["VELOCITY_DB_NAME"],
+        user=os.environ["VELOCITY_DB_USER"],
+        password=os.environ["VELOCITY_DB_PASSWORD"],
+        min_size=2,
+        max_size=10,
+        command_timeout=30,
+        # Set app_name for easier identification in pg_stat_activity
+        server_settings={"application_name": "velocity-backend"},
+    )
+    return _pool
+
+
+async def close_pool() -> None:
+    """Closes the connection pool on application shutdown."""
+    global _pool
+    if _pool:
+        await _pool.close()
+        _pool = None
+
+
+def get_pool(request: Request) -> asyncpg.Pool:
+    """FastAPI dependency: returns the pool stored in app.state."""
+    pool: asyncpg.Pool = request.app.state.db_pool
+    if pool is None:
+        raise RuntimeError("Database pool is not initialised.")
+    return pool