Algebraic quantum kinematics and SR-selection

We develop, as the first of a six-paper series, an operator-algebraic framework relating non-relativistic quantum mechanics and special relativity. Three structural facts organize the framework. (i)~The photon sector of free QED is a transparent realization: classical Fourier--Maxwell theory supplies a complex Hilbert-space scaffold (inner product, symplectic form, Schr\"odinger-form mode equation, polarization $\mathbb{C}^2$) with no quantum input, and a single canonical commutator with scale $\hbar$ on the mode amplitudes promotes it to single-photon QED, with photon indivisibility, the Planck relation $E=\hbar\omega$, and the spin spectrum $\pm\hbar$ as theorems. (ii)~The constants $c$ and $\hbar$ play non-interchangeable roles: $c$ is intrinsic to each Fourier-conjugate space, while $\hbar$ acts \emph{between} them, converting kinematic phase rates into dynamical observables. (iii)~Lifting the framework to a Haag--Kastler net with sharper-than-equal-time microcausality and positive-energy spectrum is structurally obstructed in the Galilean case; we state this as the SR-selection conjecture and identify three strands of evidence (Hegerfeldt spreading; absence of a known Galilean multi-particle resolution; Reeh--Schlieder failure on Galilean Haag--Kastler nets), the third established as a precise no-go theorem in the second paper of the series. The framework's modular content (Tomita--Takesaki, Bisognano--Wichmann, Unruh as KMS, type-$\mathrm{III}_1$ universality) is collected as the algebraic substrate on which the curved-background, dynamical-metric, and crossed-product extensions of the third through sixth papers operate.