A long <xs:simpleType> restriction chain is flat in the document, so the same base was resolved repeatedly: the named simple types were resolved by an N-pass fixpoint, and the facet-applicability variety check re-scanned the schema's children to find each base at every link of every type's chain (compiling a 600-link chain took ~4.4s). Named simple types are now resolved once in dependency order (XSDSimpleTypeOrder), and the variety check uses an O(1) name map and memoizes each type's variety (SchemaSimpleTypeVariety); the same chain now compiles in ~30ms. Behaviour-preserving, verified conformance-neutral over the full W3C XSTS corpus, the determinism differential, and the full suite.
