Function audit_stream_opened 

pub fn audit_stream_opened(
    runtime: &RedDBRuntime,
    lease_handle: &str,
    principal: &str,
    snapshot_lsn: u64,
    query_hash: &str,
)

Issue #767 / S8 — audit emission helpers. Each helper builds an AuditEvent shaped to the brief and forwards it to the runtime’s audit log. The helpers are intentionally side-effect-only (no return); audit emission must never terminate a stream that would otherwise succeed.