Function resolve_access_token 

pub async fn resolve_access_token(
    provider: &str,
    source: &CredentialSource,
    cache: &TokenCache,
    http: &Client,
) -> Result<String, String>

Provider-aware token resolution honoring the credential source — kept as a compatibility adapter for CLI callers (synaps status). Delegates to the typed credential broker: the local in-process broker or the authenticated remote transport. Vends the access token only.