Probability as Geometry: Viewpoint Multiplicity, Typicality, and the Confirmation of the Born Rule in a Block of Histories

Papers 1-2 of this series derived Born weights conditionally from the block’s Riemannian geometry: the canonical volume determines the Hilbert structure, the induced projective geometry determines the ray measure, and Gleason noncontextuality fixes the trace assignment. What remained was the confirmation problem: in a block ontology every compatible history and every compatible observer-instance exists, so probability must be a measure over realised record-relative viewpoints, not a chance of becoming actual. This paper builds the record-theoretic and statistical structure that closes that gap, up to two explicitly priced commitments. The central claim, calibrated. In a non-splitting block ontology, perfect record cells inherit the Born measure and its exact conditional calculus. Under a persistent-prefix distinguishability condition (Assumption PF, stated prominently), interference remains uniformly controlled through arbitrarily deep finite record refinements. The resulting static record filtration obeys martingale concentration without independence assumptions, and — conditional on the explicitly priced viewpoint-typicality principle (Commitment TY) — Born conditional probabilities are exponentially confirmed against persistently different rival policies, including adaptive history-dependent rivals. The supporting structure: an exact perfect-record projector calculus; a closed sequential interference bound whose index is refinement depth, not flowing time; an explicit block-compatible recorder family (translated Gaussian fragments, and intrinsically, normalised heat-kernel packets on the block’s own S3) for which the record-overlap exponents and minimum redundancy thresholds are derived in closed form — the recorder family itself is not yet derived from block dynamics; and a canonical Gram-polar construction that associates to any imperfect record family, at each fixed depth, an exact Boolean hierarchy of projectors within explicitly bounded distance of the raw records — a finite-depth canonical Booleanisation, with cross-depth projective consistency an open problem. The coherent event weight Q is used only comparatively: it is not an additive probability measure for imperfect records, and the paper states the resulting trade-off explicitly. Two commitments carry the non-mathematical load and are priced, not hidden. Commitment OL: observer continuity is represented by record-functional equivalence across compatible continuations. Commitment TY: rational expectation over the record-equivalent continuations follows the canonical conditional measure. Given TY, the block-derived Born measure is internally self-confirming on record-typical viewpoints; without it, the mathematics fixes the measure but not its first-person authority. No collapse, branch creation, privileged actuality, pointer-basis selection, or theory of consciousness is used. Finite-resolution results on the block’s S3 truncation ladder (exact spectral-leakage identities, a conditional Sobolev rate, the Gleason dimension threshold) are collected in Appendix B.