Metaglass

The material is a branch point between raw blocks and systems that use glass; plan it as a stock target only after checking its actual consumers.

When it fits: Add it when a recipe or building plan calls for metaglass.

The tradeoff: One source recipe run makes 1 and lists 1 Lead, 1 Sand at Kiln; 1 recipe variant(s) for this output are grouped together. Verify access where the pack is incomplete. Processing capacity and the feed materials are separate from the finished material amount; don't treat it as a building with an operating rate.