Typed pydantic-settings view over every IX_* env var, defaults matching
spec §9 exactly. @lru_cache-wrapped accessor so parsing/validation happens
once per process; tests clear the cache via get_config.cache_clear().
extra="ignore" keeps the container robust against typo'd env vars in
production .env files. engine.py's URL resolver now goes through
get_config() when ix.config is importable (bootstrap fallback remains so
hypothetical early-import callers don't crash).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>