Hilbert Plateau Contract for Ultrafast Squeezing: G–Σ–P–L Falsifiability with Four-Solves-Three Closure

After an extensive search, and to the best of the author’s knowledge, no prior instances of “Hilbert subspace Extended” or “Four-Solves-Three closure” appear in the ultrafast-squeezing literature and quite probably well beyond. A concise, portable protocol for ultrafast squeezing: Four-Solves-Three closure combined with a Hilbert Plateau Contract (G–Σ–P–L) and reversible triad tokens. Three phase-locked channels drive degenerate χ(3) four-wave mixing in fused silica; the nonlinearity supplies an effective fourth field, closing the system while preserving a programmable squeeze-angle knob. We map an R≈1 plateau with preregistered acceptance lines (flatness F, Delta-k·L, hysteresis, angle hygiene) and enforce falsifiers (flip-only Z, Disable-L timing slip, monotone→plateau) to create a testable contract. Each zero-centered triad is encoded as a byte-exact 24-bit token, N = R + 256G + 65536B, with a roll-up N_ALL for grouped sets; this makes replication and audit trivial. The package includes a VIS-anchor triad with ±A center shifts, a reproducibility pack (filenames, codes, CI levels), and a dated provenance note (non-assertion) documenting exactly what was prepared and made reproducible. After an extensive search, and to the best of the author’s knowledge, no prior instances of “Hilbert subspace Extended” or “Four-Solves-Three closure” appear in the ultrafast-squeezing literature (and none were found beyond it). Prior “contract-style” Hilbert uses (e.g., Bell/CHSH, entanglement witnesses) do not combine plateau geometry, falsifiability gates (G–Σ–P–L), and portable encoding.