Requirement atom

One solution-agnostic, testable requirement under a goal pillar, with done criteria and a failure mode.

Each atom names a state variable, a failure shape, the perturbation classes that would expose it, a timescale (acute, subacute, chronic or decadal), the classes of meter that could measure it, and a multiple-realizability check requiring at least three distinct architectures that could satisfy it. Atoms carry the same role split as pillars: an identification atom guards against the answer being wrong (the set miscounted, a rival set never compared).