fn extract_ambient_home_provider(combined: &str) -> Option<String>Expand description
Pulls the provider id out of
SpawnGateError::AmbientHomeDirNotAllowed’s own Display wording
(“this agent’s {provider} identity points directly at your personal …” —
identity/resolver/errors.rs). Same “return None on any mismatch rather
than guessing” contract as extract_spawn_gate_provider above.