Optics keep track of path dependency info
used in calculating state. When a node is
added/removed in the path via the mod API
(i.e. not schematics, vmanip, etc.) then the
nodes whose state decisions depended on
paths going through there are automatically
triggered for a recheck.
This should make things like furnace sand
auto-loaders respond snappily.
Granted, memory use with this approach is
a concern, but we will just have to monitor it
under normal usage patterns.
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