Where a driven signal sits in the build's array of drivers. [] as well as []. Unlike FastCompIndex this one IS a Map key - WaveData's fetch cache and WaveDrawn's memo of the SVGs, plus a Set of them for pruning - so the note above does price it. It costs nothing as shipped because both of those are RENDERER stores, where [] has already made the key a bare number and the Map is an ordinary int-keyed one. Moving either store to the .NET side would start paying for it; nothing else here would notice. SignalHandle is this index PLUS the build it belongs to: a handle can be quoted back by a reader, an index cannot, which is what stops one simulation's index reading another's data.