Function validate_session_id_for_acceptance 

pub fn validate_session_id_for_acceptance(
    session_id: &str,
) -> Result<(), MacpError>

Validate that a session ID meets the acceptance policy.

Accepts:

• UUID v4/v7 in hyphenated lowercase canonical form (36 chars)
• base64url tokens of 22+ chars ([A-Za-z0-9_-])

Rejects everything else (empty, short human-readable, uppercase UUID, etc.).