com.t0ronto.commons.attestation

A single attestation in the t0ronto data commons: one quad asserting that `subject` stands in relation `predicate` to an object. Subject is an at-uri (a project entity, or another attestation in the retracts case). Predicate is an at-uri to a project predicate entity (see scripts/predicate_seed.json). Object is exactly one of `objectRef` (an at-uri reference to another entity — an edge in the graph), `objectLit` (a scalar literal — a property value; external IRIs live here as xsd:anyURI), or `objectStruct` (a compound value such as an address or social handle). Provenance is intrinsic and is NOT carried as fields: the record is signed by the repo's DID and stamped by the commit, so who-attested-it and when fall out of the substrate. Append-only by convention — corrections are new attestations (see the retracts predicate), not edits. rkey is a TID. Phase 8: every identity in the model — subject, predicate, objectRef — is an at-uri; the only strings are literals.