Linear-size autocatalytic sets are asymptotically absent in the sparse binary polymer model

In the sparse binary polymer model with reversible ligation and cleavage, we prove that for every fixed food horizon, fixed nonnegative catalysis intensity and fixed linear reaction budget, the probability of a nonempty reflexively autocatalytic and food-generated set within that budget tends to zero, at rate O(1/n). The probability that a single molecule catalyses a self-constructing reaction set also vanishes, cleavage included. A productive-prefix argument excludes bounded catalyst counts, while an injective acyclic dependency encoding supplies a factorial saving in the count of productive reaction supports. Consequences include divergence of minimum RAF size relative to polymer length and of minimum catalyst count, together with conditional forms. Combining the lower bound with the published quadratic-witness result of Hordijk and Steel gives a superlinear-to-quadratic window. The principal estimates and consequences are formalized in Lean 4 against the literal split-position model; the published upper-witness input is cited separately.