Probes the keyring backend once (per session) and caches the result.
Returns FALSE on headless/server environments where the secret-service
daemon is absent, so callers can fall back to ~/.Renviron.
Probes the keyring backend once (per session) and caches the result.
Returns FALSE on headless/server environments where the secret-service
daemon is absent, so callers can fall back to ~/.Renviron.