Fulcrum: Quantitative, Governed Granularity for Microservice Boundaries with the RVx Inde

Abstract

Microservice migrations often produce the opposite of their promise: a distributed monolith that carries the cost of distribution without its benefits. The root cause is that service boundaries are chosen by qualitative heuristics that ignore a boundary's runtime cost, how often services actually change and execute together, and the cognitive capacity of the owning team.We introduce the RVx Index, a composite, bounded, context-calibrated score for whether a boundary adds value or merely adds distributed complexity. RVx fuses three signals usually analyzed in isolation: Kinetic Efficiency (useful computation over total transaction time, from traces), Semantic Distinctness (functional independence from version-history temporal coupling), and Cognitive Load (static complexity normalized by team capacity). We prove structural properties (boundedness, monotonicity, soft weakest-link behavior, exponent identifiability) and calibrate thresholds per domain profile. The governing principle is Khan's Law: a boundary is only as valuable as its weakest dimension.We present Fulcrum, a sense-decide-actuate-verify governance loop under a safety gate; a Saga Complexity Score for transaction topology; and KM3, a portfolio maturity model. Treating the metric as a gaming target, we give a threat model, adversarial analysis (G1-G14), and conformance requirements (N1-N23). We specify a reproducible protocol and report controlled simulation plus construct validation on a real deployed AWS benchmark.This is a framework and controlled-validation paper, not an organic-production study; predictive claims are stated as falsifiable hypotheses. A labeled extension (RVx-A) applies the same form to agent tool boundaries under the Model Context Protocol. Comments: 98 pages, 10 figures. Methods and framework paper: formal properties, controlled simulation, and construct validation on a deployed AWS benchmark; production study specified as future work. Code and reproduction: https://github.com/vaquarkhan/fulcrum-rvx