A smooth beginning for spacetime III: Wider implications and open horizons

The closing paper of the trilogy "A smooth beginning for spacetime." Papers I and II argued that the Feldbrugge–Lehners–Turok fluctuation catastrophe of the Lorentzian no-boundary path integral is real, unmodifiable, and unnecessary to evade: the de Sitter geometry hosting the biased saddle also hosts the thermodynamic machinery that erases the bias, with the budget closing identically. This third paper surveys the mechanism's reach, ordered by decreasing certainty and visibly tagged. Tier one: a two-branch, CPT-resonant beginning protected by an exact antisymmetry; a de Sitter graviton with no quasinormal tone yet a universal relaxation floor 3H; the reality lock abstracted into a portable screen on cosmogonies. Tier two: the boundary between thermal erasure and backreaction-driven dilution, derived as the adiabaticity condition of the coupled flow, with the erasure dividing the cosmological constant in closed form, Λ_f = Λ_i/(1+σ) — Principle 3, the Principle of Exact Settlement. Tier three: the entanglement thread, a sensitivity inventory for quasi–de Sitter, a two-branch CMB reading bracketing the observed low quadrupole from opposite sides with one conditional B-mode discriminant readable by a LiteBIRD-class survey, and seven open problems anchored to gated objects. The record includes the paper, all figures, the cited working record (programme memo plus gate scripts and logs), and the figure code; every quantitative statement traces to a gate, and Appendix A holds the audit. Drafting and computation were assisted by a large language model (Claude, Anthropic); the author takes sole responsibility. No specific funding was received.