The Physics Tax — The Coherency Bill Your Hardware Runs Before the Protocol Speaks
Hardware runs a coherency bill on every distributed system before any protocol is chosen. Cache invalidation, NIC saturation, and memory bus contention set a throughput ceiling that grows quadratically with node count under the Universal Scalability Law — a ceiling no software optimization can move. Tail latency fans out geometrically through every microservice hop, invisible to average-latency dashboards. Both are irreducible. The Pareto Ledger — fitted coherency coefficients kappa+beta, measured N_max, coordinated-omission-free P99 — converts these pre-protocol costs into documented numbers before any architecture decision is made.