Function sql_error_response 

pub fn sql_error_response(
    status: u16,
    code: &str,
    message: &str,
    sqlite_code: Option<i32>,
    retry_scope: &str,
    transaction_state: Option<&str>,
) -> (u16, Value)

Build one public SQL error body: {code, message, retry_scope} plus the optional sqlite_code and transaction_state keys. Returns (status, body); the hosts wrap the pair in their own HTTP layer (C7 — response wrapping stays per-host).