Terminal subprocesses inherit OPENAI_BASE_URL and other provider env
vars loaded from ~/.hermes/.env, silently misrouting external CLIs
like codex. Build a blocklist dynamically from the provider registry
so new providers are automatically covered. Callers that truly need
a blocked var can opt in via the _HERMES_FORCE_ prefix.
Closes#1002
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>