Function is_duplicate_state 

fn is_duplicate_state(
    event_type: &StateEventType,
    sender: &UserId,
    content: &CanonicalJsonObject,
    current: &PduEvent,
) -> Result<bool>

Whether an incoming state event is a content-identical resend by its own author.

The caller’s guard returns before state_res::auth_check runs, so every conjunct gating that early return must be a version-invariant fact that can only suppress a dedup, never permit one. Membership class qualifies; power levels and per-type rules do not, and wanting an exact status code there is a reason to move the guard after authorization rather than to add a conjunct.