pub const DECLARED_PRIMARY_KEY_COLUMNS: [&str; 8];Expand description
The primary-key (tag) columns, in key order. Starting with the source endpoint
makes out-edge lookup (WHERE src_type=? AND src_id=?) a key-prefix scan;
provenance and generation_id are in the key so a declared edge and a
(future) derived edge for the same pair coexist without clobbering.