Summary

• add schema validation for directive definition cycles, including indirect cycles through input types
• keep a minimal SDL pre-check to stop recursive directive construction before schema validation can run
• add SDL and programmatic schema tests covering direct and indirect directive cycles

Testing

• ./gradlew test --tests graphql.schema.idl.SchemaTypeDirectivesCheckerTest --tests graphql.schema.validation.DirectiveReferencesAreValidTest --tests graphql.schema.validation.SchemaValidatorTest
• ./gradlew clean test (run locally with a temporary init-script workaround to remove duplicate main output directories from the test classpath; vanilla ./gradlew test in this workspace currently hits an unrelated ArchUnit classpath issue)