auth-source lookup behavior and prompting in non-interactive sessions

Credential Lookup Policy

Emacs auth-source supports pluggable backends for secrets, allowing a dedicated test store to be used for integration testing without production credentials. Lookup order is governed by auth-sources and preferred backends.

Backend Fallback Uncertainty

When a requested secret is absent, behavior is backend dependent. Some backends return nil silently while others attempt interactive prompting for missing information or GPG passphrases. In headless or batch-mode environments this inconsistency can produce non-deterministic outcomes.

Current documentation does not specify a uniform policy for missing keys in non-interactive sessions across Emacs versions.

• Does auth-source provide a mechanism to globally disable interactive prompting during a lookup?
• Is there a documented way to ensure auth-source-search returns nil without blocking for input in batch mode?