Simplex

object Simplex mixes in SimplexOps (SimplexOps.scala) rather than the trait's methods living as a separate top-level extension clause: extension methods declared in the opaque type's own companion object are found via the receiver type's implicit scope, not via blanket top-level visibility across the package -- the fix for the same-named top-level extension collisions documented in .claude/WORKLOG-extension-companion-objects.md. underlying moved in here for the same reason, even though nothing currently collides on that name -- keeping every Simplex[VertexT]-receiver extension routed through one place is what makes "a future opaque type may reuse this name" actually hold.

asSimplex (below, top-level, NOT moved in here) is a real exception, not an oversight: its RECEIVER is SortedSet[VertexT], not Simplex[VertexT] -- companion-object extension lookup is keyed by the receiver type, so an extension on SortedSet[VertexT] placed inside Simplex's companion is never found from a SortedSet[VertexT] receiver. It was also never part of the naming collision in the first place (asSimplex/asCube don't share a name), so there's no reason to move it either.