Fitness Functions

Goal

Make architecture an executable, enforced thing rather than a diagram that rots. A fitness function is an objective, measurable test of an architectural characteristic — the evolutionary-architecture mechanism for governing the "-ilities" the same way unit tests govern logic. Where a unit test asserts a feature works, a fitness function asserts a structural property holds: cyclomatic complexity stays under a limit, the domain layer never imports infrastructure, p99 latency stays inside its budget, afferent/efferent coupling stays bounded. Wired into CI, fitness functions turn architectural intent into automated governance that fails the build the moment the system drifts away from its target characteristics.