  We propose an algorithm which builds a concrete dual for large-radius 3d de
Sitter with a timelike York boundary for both gravity and bulk effective
fields. This generalizes the solvable $T\bar T+\Lambda_2$ deformation, whose
finite real spectrum accounts for the refined Gibbons-Hawking entropy as a
microstate count while reproducing the radial static patch geometry. The
required generalization to produce approximately local boundary conditions for
bulk quantum fields requires a scheme for defining double-trace operators dual
to deformed boundary conditions to realize the finite timelike boundary, valid
at finite N. By starting with a small stint of a pure $T\bar T$ trajectory, the
theory becomes finite, enabling well-defined subtractions to define the
double-trace deformation so as to match the large-N prescription of Hartman,
Kruthoff, Shaghoulian, and Tajdini to good approximation. We incorporate the
matter effecting an uplift from negative to positive cosmological constant, and
analyze the effect of matter on the energy spectrum of the theory arising from
time-dependent bulk excitations. This validates the cosmic horizon $dS_3$
microstate count for large-radius $dS_3$ holography, embedding $T\bar
T+\Lambda_2$ concretely into a larger theory consistent with bulk locality for
matter fields. We comment briefly on potential upgrades to four dimensions and
other future directions.
