GCFT CDN-169: The Sound and the Floor — c_s Derived, the CDN-168 Floor Exposed as Artifact

CDN-169 half-pays theory debt D6 and corrects the chain's newest claim. The solid half: plane waves in the CDN-163 linearized spintessence system give the gapless branch Ω² = k²(k²+Δ)/4ω₀², hence a derived sound speed c_s = √Δ/2ω₀ — set by the same anharmonicity that controls the CDN-163 channel split. The Branch-A requirement c_s ~ (2.2–4.8)×10⁻³ maps to Δ/ω₀² ≈ (2–9)×10⁻⁵, a nearly harmonic potential, internally consistent with the fully radial wake found there. The corrective half: the drag peak does not track c_s at small Δ in the σω ≲ 8 regime (floor ≈ 0.15), but re-examination of CDN-168's large-σ data shows F(v) rising monotonically to the last sampled velocity at σω = 16 and 32 — the "quasi-universal floor," the load-bearing step in the canonical-kinetics exclusion, was a grid-edge artifact. The exclusion is withdrawn as unestablished; CDN-168 is downgraded in place (v* = 0.15·c_Ξ valid only for σω ≲ 8; fork retained, both branches open). The decisive run is pre-registered for CDN-170: σω ≥ 32, v ∈ [0.005, 0.1], steady state at the lowest velocities, transient and sponge diagnostics — v* ∝ 1/(σω₀) rescues canonical kinetics and maps the window to Δ via c_s; a persistent floor re-establishes the exclusion. The CDN-167 interval and DR4 velocity sort are unaffected. Figure and results JSON included. By Nicky Hacquier (Aporion Dynamics) — Project Aporion; follows CDN-168 (DOI 10.5281/zenodo.20636460).