Gravitational-Wave Recoil as Medium Dynamics: RBH‑1 as a Test of Space‑Phase (SP3)

Gravitational-wave recoil of black holes is conventionally described within GeneralRelativity as a consequence of anisotropic radiation of spacetime curvature. Operationally,however, this process already endows spacetime with properties characteristic of a physicalmedium: the ability to carry momentum, store stress transiently, and deliver a net impulse.In this paper we argue that the recently confirmed runaway supermassive black holeRBH‑1, observed with JWST/NIRSpec as a supersonic bow shock and kiloparsec-scale wake,provides a unique laboratory for probing what else this effective medium does. We frameRBH‑1 within Space‑Phase (SP3) theory, in which spacetime is treated as a carrier capableof conditioning, corridor formation, and memory. While gravitational-wave recoil orthree‑body slingshot interactions plausibly supply the initial kick, the observed wakemorphology, coherence, and persistence motivate discriminating tests between a purelydiffusive geometric interpretation and a structured medium with relaxation times. Twoschematic figures are provided to delineate observational discriminants that can be testedwith existing and forthcoming data.