Dependency-free Java representation of JSON:API v1.1 documents, with local construction invariants and aggregate document validation.

ResourceObject resource = ResourceObject.of("articles", "1");
JsonApiDocument document = JsonApiDocument.withData(
    new DocumentData.SingleResource(resource));

new JsonApiDocumentValidator().validate(document, ValidationContext.defaults());

Construct model values first; their constructors enforce invariants that need only the value being created. Run JsonApiDocumentValidator for identity uniqueness, full linkage, document usage, endpoint role, link context, and extension/profile policy. The conformance checklist owns the current rule inventory.

Java null on a containing component means that a member is absent. Sealed model variants represent explicit JSON null, single, and collection forms. Present-empty wrappers and collections remain distinct from absence. ErrorObject.builder() and ErrorSource.builder() construct the same immutable core values as direct constructors.

• Core has no functional third-party runtime dependency; JSpecify is compile-only metadata.
• It provides no Jackson codec or mapping, HTTP adapter, query parser, persistence integration, or extension-specific semantics.
• Valid extension and @ members are preserved without interpretation.
• Validation failures use JsonApiValidationException, a stable ValidationRuleCode, and a JSON Pointer-like path.
• The package dependency direction is aggregate → model/internal/validation, model → internal/validation, and internal → validation; reverse edges are forbidden.

See the architecture overview, ADR-002, and ADR-003.