Every component of one sheet instance, by its design-time id. Keyed by the bare int INSIDE a ComponentId, and reached only through the SimGraph module below, which takes and returns the wrapped type. F#'s Map takes its comparer from LanguagePrimitives.FastGenericComparer, which has hard-coded fast paths for genuine primitives and a boxing fallback for everything else - so an int key is 2.4x faster than a reference wrapper and a struct wrapper is slower than either, boxing BOTH operands on every comparison. Unwrapping at this one boundary buys the primitive path and keeps the types at every call site, which is what lets ComponentId be [] without this map being the thing that pays.