Function compatible_auth_method 

pub fn compatible_auth_method(
    source_method: &str,
    effective: &FamilyRecipe,
) -> Option<&'static str>

Maps one provider-level credential method onto the wire auth expected by an effective model family. Only equivalent credential semantics are mapped: single API keys may change header/bearer encoding, and an explicit access token may become bearer auth. AWS static credentials never cross families.