Function audit_log_invocation 

pub fn audit_log_invocation(
    service_id: &str,
    function_name: &str,
    row_count: usize,
    latency_ms: u64,
    validation_ok: bool,
    worker_identity: Option<&str>,
)

Audit-log a remote UDF invocation.

SECURITY: never logs payload data — only service/function identity, row count, latency, worker identity, and the validation outcome.