fitness-functionslisted

# Architectural Fitness Functions ## Overview Architectural fitness functions are periodic automated checks that verify system-wide architectural properties. The concept comes from Ford, Parsons, Kua & Sadalage's *Building Evolutionary Architectures* (O'Reilly, 2017/2022). Their key insight: architecture degrades not through single bad changes but through accumulated small violations. Each individual change looks reasonable in isolation. The damage is cumulative and invisible until it becomes painful. Fitness functions catch the accumulation that per-change constraints miss. They answer questions like: - Has coupling between modules A and B increased over the last month? - Are any files becoming complexity hotspots — high churn correlated with growing cognitive complexity? - Do all modules still respect declared layer boundaries? - Is test coverage declining in the most architecturally significant layers? These checks are too slow or expensive for every PR (full dependency graph analysis, coupling metric computation, churn-complexity correlation). But they are too important to skip entirely. The GC system's weekly cadence is a natural fit. --- ## The Constraint vs Fitness Function Distinction A constraint gates individual changes. A fitness function measures system-wide properties over time. Both are harness enforcement, but at different timescales. | Aspect | Constraint | Fitness Function | | --- | --- | --- | | Scope | Per-change (commit or PR) | System-wide (w