Value-free telemetry. Owns the metadata allowlist — the single enforcement point for "no row value in telemetry". An off-allowlist key raises rather than shipping a value downstream. Mirrors replicant/ash_arcadic.

The allowlist gates metadata KEYS. Values under an allowlisted key (reason, table, tenant?, resource, …) remain the caller's value-free responsibility — pass atoms, modules, integers, or booleans, never a raw row value or DB message.