A flat chain of <xs:group> references is not bounded by the parser's maxDepth (the definitions are siblings, not nested), so the compositional UPA determinism check's lazy per-reference recursion overflowed the native 8 MB stack while compiling a legal schema. Group summaries form an acyclic graph, so they are now precomputed bottom-up in dependency order (GroupDependencyOrder): the walk's group lookup is a cache hit and recursion is bounded by a single group's own model nesting. The precomputed reachable set is identical to the lazy walk's, so the verdict is unchanged. Verified verdict-equivalent over the full W3C XSTS corpus, the libxml2 determinism differential (0 FP, same 3 FN), the full suite, and an adversarial critic. Residual, tracked: the particle compiler that inlines a group reference still overflows on a far longer chain; closing it needs a content-model nesting-depth limit with a located error.
Mihaela Mihaljevic
1f8d99adfc