Module credential 

Multi-source credential resolution.

Reads API keys from multiple sources with clear priority:

1. config.toml → [engine].api_key (explicit override)
2. ~/.oxi/auth.json (shared with oxi CLI if installed)
3. oxi-ai env var fallback (CI/CD, containers)

Structs

CredentialStore

Multi-source credential resolver.

Enums

CredentialSource

Where a credential was found.