This paper presents a minimal demonstrator of boundary-first ecological coherence sensing, translating previously proposed architectural principles into a practical, testable implementation. The system combines distributed boundary sensing, local hexagonal filtering, inward signal compression, and toroidal phase integration to produce an Ecological Coherence Index (ECI) from continuous environmental signals. The demonstrator is intentionally small in scope and focuses on validating the operational loop rather than large-scale ecological deployment. Measurable outputs include variance reduction during coherence filtering, boundary-to-interior detection timing differences, and coherence dependency tests using phase scrambling controls. These measurements provide empirical grounding for the TRIDENT-Z0 validation framework introduced in earlier work, enabling explicit testing of interior locking, boundary flow, constraint behaviour, and coherence collapse. The goal of this work is to establish a reproducible reference implementation that bridges conceptual architecture and real-world experimentation. By demonstrating a functional sensing loop with measurable outputs, the paper acts as an expansion node within the broader boundary-first ecological sensing corpus, supporting future replication, scaling, and comparative studies. boundary-first sensing; ecological coherence; reference implementation; passive sensing; hexagonal lattice; toroidal integration; phase-based monitoring; distributed sensing; coherence index; validation framework; TRIDENT-Z0; biomimetic sensing; ecological monitoring; systems demonstrator; reproducible framework; passive environmental sensing