Function parse_codex_usage 

pub fn parse_codex_usage(
    body: &str,
    account_label: &str,
    observed_at: u64,
    expected_account_id: Option<&str>,
) -> Result<UsageSnapshot, UsageError>

Parse GET /wham/usage. expected_account_id is the id derived from the bearer token; a differing response account_id fails closed.