The Standard Coherence Fidelity Layer (SCFL) Companion Field Guide V1₂

---The Standard Coherence Fidelity Layer (SCFL) Field Companion v1.2 is the operational specification for a candidate measurement standard designed to quantify coherence degradation and rupture precursors across complex systems. The document formalizes the full measurement architecture of the SCFL: canonical definitions of four time-varying functions — C(t) (coherence field), F(t) (fragmentation), D(t) (drift), and R(t) (rupture envelope) — together with the Coherence Degradation Index (CDI), a scalar instrument bounded on 0,1 that aggregates stability, phase alignment, fragmentation entropy, drift velocity, and rupture-envelope proximity into a single reproducible reading. The Field Companion describes the canonical operator module, a complete field measurement protocol, a validation checklist, and a structured falsification criteria set intended to make the instrument assessable rather than merely applicable. The document is not a forecasting model and is not software. Its claim is methodological: that coherence, appropriately formalized, constitutes a measurable upstream property whose degradation geometry is consistent across substrates and timescales, and that this consistency can be tested.The motivating result reported in the companion corpus is a consistent four-stage degradation geometry — Early Fragmentation, Phase Misalignment, Drift Acceleration, Rupture Cascade — observed across systems spanning four orders of magnitude in temporal scale. Two canonical cases are analyzed in detail: the ERCOT grid instability event (real-time infrastructure) and the Flint water crisis (slow-time governance failure). In both cases, CDI trajectories exhibit the same geometric progression preceding rupture despite the cadence difference. This cadence invariance is presented as a candidate property of the instrument, not a confirmed universal law, and is subject to the falsification conditions specified in the companion falsification protocol (Brogdon, 2026, https://doi.org/10.5281/zenodo.19426211). A structured 27-signature universality trial, reported in the Virtual Lab specification (Brogdon, 2026, https://doi.org/10.5281/zenodo.19722528), found 19 of 27 candidate coherence signatures surviving cross-domain testing, establishing a constrained — not universal — basis for candidate invariance. The Field Companion’s domain deployment guide and proof structure draw directly on these results while acknowledging that cross-substrate generalization beyond tested domains remains an open empirical question, as noted in the preregistered validation protocol (Brogdon, 2026, https://doi.org/10.5281/zenodo.19474694).The SCFL is positioned in relation to existing work on complex systems and early-warning measurement. Scheffer et al. (2009, Nature) established the theoretical basis for early-warning signals preceding critical transitions; Carpenter and Brock (2006) and Dakos et al. (2008) formalized rising variance and critical slowing down as measurable precursors to regime shifts. The SCFL’s CDI draws on these foundations while attempting to extend them into a unified, substrate-agnostic measurement layer rather than a domain-specific indicator. The coherence field formalism is informed by network science treatments of coupled systems (Barabási) and follows conventions from established psychophysiological instrumentation, including HRV measurement standards (Task Force, 1996, Circulation). The Field Companion makes no claim that SCFL supersedes or replaces these frameworks. It proposes a complementary instrumentation layer whose relationship to existing early-warning methods requires independent empirical adjudication. Coherence measurement is treated here as a candidate discipline — not an established standard — and the instrument is offered in that spirit.The Field Companion is released to invite critical evaluation. The canonical falsification condition for the SCFL is Invariant Disagreement Under Controlled Equivalence: two independent operators working from identical structural inputs and boundary conditions must derive identical invariant behavior. If they do not, the instrument fails at the root. Researchers who identify conditions under which CDI geometry does not hold, under which the four-stage degradation sequence does not precede rupture, or under which independent operators applying the protocol reach structurally inconsistent results are encouraged to document and publish those findings. The value of this Field Companion depends entirely on whether the measurement standard it specifies survives contact with data and independent replication. SCFL Reference Implementation Notebook file.