DCRP77/X72R60: Directional-Stretch First Crossing and the Tilt Cost

Continuing from the sole X-free escape candidate left by DCRP76 — the infinite, non-closed 2γ stretch-selection conveyor (the material carrier must stay above DCRP61's neutral Floquet threshold while the Euler observer must stay below it) — this round derives the exact non-aligned directional-stretch equation governing 'crossing this threshold'. Defining λ_ω=ξᵀSξ and the torsion τ_ξ=Sξ-λ_ωξ, it proves the general identity D_sλ_ω+λ_ω+|Ω|²/6=2|D_sξ|²-ξᵀE_pξ, which reduces exactly to DCRP62's aligned formula when D_sξ=0. From this identity it follows that 'first crossing' must pay a hard cost of at least γκ/2: crossing dynamically must be paid for in vorticity tilt or a negative axial X72 pressure response; if 'pure selection' is used instead, drawing on already-highly-stretched material, then the inflow stretching variance and the selection distortion must satisfy a quantitative covariance gap greater than γκ/2, or else new material must be injected. The conclusion is that only two cases remain for the surviving X-free branch — a 'genuinely tilting selection conveyor' or a 'non-compact, pre-selected high-stretch reservoir' — leaving DCRP78 to test whether the tilting action required by the former can stay silent toward the transverse pressure response.