Minimal Spherical Kinematic Description of the Observable Cosmic Record: A Reduction Method Separating the Photonic Trace from the Dynamical Scale

This paper investigates how far the observable cosmic record can be described while introducing the smallest possible number of prior conceptual assumptions. The starting construction is a spherical observational domain centered on a local reference point. The sphere is not introduced as a claim about the geometry of the entire Universe, but as an organization of radially accessible information. A strict distinction is made between the radial boundary of accessible observation, a possible dynamical boundary of the model, the photon frequency carrying information, and the cosmic expansion rate H(z). Using DESI DR2 BAO data, two dimensionless quantities are defined, Gγ = 1/(1+z) and ΦD = H(z)rd/c = 1/(DH/rd). Their product P = ΦD·Gγ is proportional to ȧ within standard cosmological kinematics, while the logarithmic slope Qs = -d ln(P)/d ln(Gγ) is mathematically identical to the standard deceleration parameter q. The work therefore does not claim a new cosmological parameter, but proposes a controlled methodological separation of observation, mathematical transformation, kinematic inference, and physical interpretation.