Function empty_transit_metadata_cbor 

pub fn empty_transit_metadata_cbor() -> &'static [u8] 

Sentinel for dependencies_metadata / objects_metadata on streams that don’t use the transit/POD wire format (e.g. OTLP). Existing readers decode these BYTEA columns as Vec<UserDefinedType> and iterate; an empty Vec makes those loops no-ops without touching consumer code.