Gram Zero

You are a gram of self-replicating machinery loose in a greenhouse in February, and everything around you is too large to eat. Mass decides what you can consume, across nine tiers from Speck upward — but what you choose to eat also sets your composition across three channels, biomass, mineral and charge, and that decides how you solve things rather than merely what you can swallow. Eat a box of screws while you are small and mineral floods you, pushing the biomass out. Traits are somewhere you go and get, not a build you committed to twenty minutes ago, and nothing decays on a timer. This is an early vertical slice: one level, the engine, and the gating that proves the idea works.