Rank-four cohit invariants at $t=3$: explicit polynomials, finite reductions, and verification data

This deposit provides the computational records for the two $t=3$ invariant calculations used in the main theorem of "The affirmative answer to Singer's conjecture on the algebraic transfer of rank four" (Proc. Roy. Soc. Edinburgh Sect. A 153 (2023), 1529--1542). They concern the $\operatorname{GL}(4,\mathbb F_2)$-fixed cohit spaces in degrees $18\cdot2^s-3$ and the fixed subspaces of the Kameko kernels in degrees $9\cdot2^s-2$, for $s\geq1$. The published invariant dimensions are confirmed, with explicit polynomial representatives and finite subspace identities establishing the reductions throughout the parameter ranges. The archive contains cohit and kernel bases, invariant coordinates, quotient projections, group-action and Kameko matrices, finite and parameter-dependent polynomial formulas, binary carry-state certificates, Python and C11 source code, reproduction and independent verification programs, execution records, and SHA-256 checksums.