Horizon Monism: Gauge Symmetry, Chiral Matter and Emergent Gravity from Finite Readouts of an Octonionic Relational Structure

Horizon Monism describes physics as finite, lossy readouts of a single relational totality with no primitive time, metric or probability. Each reference horizon reads a compressed image of the whole rather than of a local region, and the flag $\mathbb{R}\subset\mathbb{C}\subset\mathbb{H}\subset\mathbb{O}$ inside one octonion algebra is its hierarchy of distinguishability; a normed visible-layer principle selects $\mathbb{O}$ as the top layer, and marked flags form the single orbit $G_2/U(2)$. The observable carrier is the exceptional Jordan algebra $\mathfrak{h}_3(\mathbb{O})$, the only simple formally real Jordan algebra without a faithful associative embedding. We construct a positive, trace-preserving expectation onto $\mathfrak{h}_3(\mathbb{C})$ and a Peirce readout onto a qubit corner; these gauge-covariant maps induce ordinary density matrices and Born probabilities and have an explicit positive product-loss defect. The nested Jordan pair fixed by the flag has stabilizer $S(U(3)\times U(2))$; an exterior module gives an anomaly-free chiral generation with a neutral singlet; the two-layer invariant space is three-dimensional, and three-layer invariants contain an exchange-odd sector whose lightest state is stable when the exchange is exact. Strict merges of a finite readout carry a positive distinction deficit that defines an acyclic temporal order. Gravity is treated as an emergent equation of state, not a quantized metric: a heat-kernel response weighted by the horizon misalignment of an octonion automorphism gives positive cosmological and Newtonian coefficients controlled by one weight, $\Lambda=M^2w/(1-w/3)$, with leading coefficient $3/2$, and projector connections realize de Sitter vacua. Masses, mixing angles and relic abundances are not yet fixed; the required dynamical calculations are stated.