Deterministic synthetic RDF

Use generate() by default and inject an independent ShaclValidator. Import
shaclEngineValidator() from @jeswr/synthetic-rdf/validate when shacl-engine is available.
generateUnchecked() is an explicit escape hatch only for exact inputs already validated in CI.

Load-bearing rules

• Pass a stable string seed; never introduce ambient entropy.
• Pass now whenever a temporal default can fire. Do not read the wall clock in a plugin.
• Plugins may draw only from context.random; fork it for logically separate choices.
• Preserve coordinate identity: shape IRI, instance index, predicate path, and occurrence determine
  a stream. Do not add shared sequential random state.
• Use { fragment } for identities that solid-seed will rebase. Use { external } only for real
  absolute IRIs, and exact-list each one in allowedExternalIris.
• Treat an override as replacement of the property's full value set. Never post-process generated
  quads to implement a persona.
• Keep shapes and ontology graphs caller-supplied. The package performs no fetch or RDF parsing.
• Serialize through SyntheticRdfResult.toTurtle() so canonical quad order and prefixes remain
  stable.

Resolution and failures

Resolution order is override, sh:hasValue, sh:in, sh:node/sh:class, datatype facets,
pattern, plugins, defaults. The selected tier drives generation; every other supported constraint
is still checked. Unsupported constraints, recursive shapes, invalid overrides, and failed
independent validation are errors, never best-effort output.

Tests

Pin seed and now in golden tests. For a new constraint, test its driving tier, conflicting
conjunctive facets, deterministic output, and an invalid override. For a plugin, test that changing
an unrelated coordinate does not perturb its output.