We introduce G-walk nucleonics: the application of orbit-occupancy theory to nuclear reactions. The state of a nucleus is represented as an orbit-occupancy vector $\mathbf{v} = (\nu_1, \nu_2, \ldots, \nu_k)$ on the shell-model single-particle levels, and elementary nuclear reactions are ISA opcodes acting on $\mathbf{v}$: FLIP (neutron/proton capture), FLOP ($\beta$-decay), SPLAT (fusion), SPLIT (fission), TWIST (nuclear isomerism), and ORBIT (closed reaction cycle). Three zero-parameter benchmarks are demonstrated. (i) All seven established nuclear magic numbers (2, 8, 20, 28, 50, 82, 126) are identified as tropical vertices of the nucleon orbit-occupancy register — orbit-complete configurations at large single-particle energy gaps — by direct analogy with noble-gas stability in chemistry (7/7). (ii) The rate-limiting step of the CNO stellar fusion cycle is correctly identified as the ${}^{14}\mathrm{N}(p,\gamma){}^{15}\mathrm{O}$ capture from the minimum log-rate criterion $\log S_0 + \Gamma_\mathrm{Gamow}$, without nuclear structure calculation. (iii) The three r-process abundance peaks at $A \approx 80, 130, 195$ are predicted as tropical fixed points of the FLIP/FLOP dynamics at magic neutron numbers $N = 50, 82, 126$, with $|\Delta A| \leq 1$ (3/3). In the Maslov–Gibbs Einsum framework, the peak location is the tropical fixed point (zero parameters); the peak width is controlled by the inverse temperature $\beta$ at r-process conditions. The quark model and lattice QCD describe sub-orbit structure; G-walk nucleonics describes which orbit is occupied — the same coarse-graining that makes G-walk chemistry a replacement for DFT in coordination chemistry, now applied one level deeper in the hierarchy of matter. The lanthanide production responsible for kilonova reddening in GW170817 is the fingerprint of the $N=82$ tropical fixed point confirmed by gravitational-wave astrophysics without any parameter fitting. Keywords nuclear shell model, magic numbers, tropical geometry, orbit occupancy, CNO cycle, r-process nucleosynthesis, stellar nucleosynthesis, kilonova, GW170817, Origami ISA, Maslov–Gibbs Einsum, beta decay, nuclear fusion, nuclear fission, isomerism, Fano plane, TRS framework