RLDS V: Microphysical Emergence of Regime-Limited Dark-Sector Dynamics — A Representative Reduction from Interacting Field Theory to the RLDS Attractor

Part V of the RLDS series. This paper develops a representative microphysical descent to the RLDS framework. Starting from an interacting dark-sector field-theoretic picture, it shows how the effective RLDS attractor dynamics can emerge at the reduced level and clarifies the relation between microphysical interaction, effective coupling, switching behaviour, and the one-dimensional autonomous RLDS ODE. The paper is not presented as a unique final microphysical completion, but as a representative reduction that demonstrates the physical plausibility of the RLDS attractor framework and its connection to interacting dark-sector dynamics. Paper I: singular-attractor prototype mathematics. Paper II: canonical RLDS framework and reduction criteria. Paper III: paired observational signature. Paper IV: cosmological consequences under RLDS closure. Paper V (this work): representative microphysical descent to RLDS.