# example Audited Bridge Artifact B: Nontrivial Constraint Graph (Mixing Chamber)

## Overview

RU is a certificate engine for universality and obstructions in constrained nonnegative propagation. Host structures supply finite inputs. Outputs are audited certificates or finite obstruction witnesses.

## What is shipped

| Artifact | Role | Path |
|---|---|---|
| Host model | Templates + 2-state constraint graph with a tight-gap separating identity edges | `sources/ru_bridge/fibonacci_constraintgraph_mix_model.json` |
| RU robust certificate | Tight core, Doeblin word, RC1, rate pack, ε* | `sources/ru/robust_certificate_fibonacci_constraintgraph_mix.json` |
| Bridge wrapper | Reduction record pointing to the proof carrier | `sources/ru_bridge/bridge_certificate_fibonacci_constraintgraph_mix.json` |

## Key certified facts (what is actually proved)

- Tight gap γ = alpha > 0 separates identity loops from the tight core.
- Tight core is aperiodic (period 1), so mixing is structurally possible.
- Doeblin word w=(A_tau,A_tau) is strictly positive on the full cone (δ=1, U=2).
- RC1 holds with B=0 on the tight core, so Doeblin blocks are unavoidable.
- Therefore normalized products contract projectively with τ=1/3 and an explicit exponential rate (see rate_pack).

This is “ posture” because the claim is carried by a machine-auditable object, not narrative.

