A growth-sector observational target for GCV on the GR-exact branch: Fixed ruler-free geometry, small coherent perturbation-sector response

Mirror record This OSF entry mirrors the Zenodo publication of the paper: Germund Johansson (2026). A growth-sector observational target for GCV on the GR-exact branch. Version 1.0.0. Canonical publication DOI: https://zenodo.org/records/18933386 The Zenodo DOI should be used for citation. This OSF record is provided as a stable mirror and for project-level archiving within the broader GCV research program. This note identifies the most natural near-term observational target of the Gauged Constant Vacuum-Mode (GCV) framework on the GR-exact branch. The central idea is simple. If the GR-exact GCV branch is the correct late-time description, then late-time ruler-free geometry remains consistent with general relativity plus a constant cosmological term once Lambda_eff is fixed by data. Any residual observable signal is expected to appear first in the perturbation sector, not as a large persistent background drift. In practical terms: geometry stays Lambda-like; growth tilts. Using the existing GCV linear-response template, UV-mapped benchmark amplitudes, and the public DESI DR1 compressed growth-ratio block, this note formulates a concrete survey-facing target: a small coherent low-redshift-enhanced growth response, with a corresponding lensing-side effect that should be correlated in sign and broad trend. The paper introduces a theory-matched low-z versus high-z tilt diagnostic, a matched-template compression, and a Fisher-style detectability estimate for the current public six-bin growth block. The main result is deliberately modest. Current public compressed growth data do not detect the benchmark GCV response, but they also do not exclude it. The matched-template and Fisher analysis show that the current public growth block is already close to optimal for this template, yet still far too noisy to test the benchmark amplitudes directly. The value of the present data is therefore target definition rather than discovery. This note does not claim evidence for modified growth, does not provide a full joint growth+lensing likelihood, and does not reinterpret current dark-energy preferences as evidence for GCV. Its purpose is narrower and cleaner: to define a falsifier interface. If future data continue to prefer ruler-free GR+Lambda geometry while growth and lensing reveal a common small low-redshift-enhanced tilt of the predicted type, that pattern would match the natural observational target of the GCV response sector. If instead geometry requires robust non-Lambda behavior, or perturbation observables prefer large, persistent, or qualitatively incompatible departures, then the minimal GR-exact branch or its bounded response sector is under pressure. Companion position within the GCV stack: this note sits alongside the GR-exact backbone, the residual-Lambda_eff interpretation, the RulerFree late-time interface, the DESI compressed growth-response constraint note, the semi-explicit UV existence proof and response mapping, the bounded-departure claim-boundary note, and the flagship CCP synthesis record. Project homepage: https://johansson.digital Project overview hub: https://github.com/gcv-framework/gcv-vacuum-energy