M21d Generalised ONS Theory: Olympus Programme, Paper IV: The g-ONS Framework, Anti-Symmetry of the Zeta Flow, No-Off-Line-Birth as a Proved Property, and the Narrowing of the RH Gap to a Single Technical Conjecture

M21d unifies all constructions of the Olympus Programme into a single Generalised Operational Number System (g‑ONS) framework, encompassing symmetric ONS, asymmetric a‑ONS, and real‑valued systems. It identifies the rank‑blind properties shared by all g‑ONS (Operational Theta universality, critical strip, Abel zeta identity) and separates them from rank‑specific features such as commutativity, functional equations, and Bell‑tower behavior. The central technical result is the Anti‑Symmetry Theorem for the Dynamic Zeta Flow: for every ONS étage carrying the self‑dual functional equation, the flow velocity satisfiesF(R,1−s)=−F(R,s). This implies Midpoint Conservation, proving that any zero birth event must occur at ℜ(s)=1/2. From this, No‑Off‑Line‑Birth is established as an unconditional theorem for all ONS étages. Combining these results with the previously established birth‑of‑zeros structure, M21d sharpens the Riemann Hypothesis to a single remaining gap: the Birth Continuity Conjecture. All other steps are proved. RH follows if and only if joint continuity of (R,s)↦ζR(s) is established, equivalently uniform convergence of the rank‑dependent Euler product. The paper precisely formulates this gap and outlines three concrete strategies toward its resolution.