"""Minimal .env loader (architecture L12: secrets from env/.env, nothing hardcoded).

Deliberately tiny: KEY=VALUE lines, comments and blanks ignored, existing
environment variables never overridden (real env wins over the file).
"""

import os
from collections.abc import MutableMapping
from pathlib import Path


def load_env_file(path: Path, env: MutableMapping[str, str] = os.environ) -> None:
    if not path.exists():
        return
    for line in path.read_text().splitlines():
        line = line.strip()
        if not line or line.startswith("#") or "=" not in line:
            continue
        key, value = line.split("=", 1)
        key = key.strip()
        if key and key not in env:
            env[key] = value.strip()