No External Dimensional Scale at the Level of Admissibility

The admissibility structure of Foundation M is built on a single primitive dimensional scale cBI entering the Born Infeld bound (A3 A4). We establish a structural rigidity result (Level 1): any deformation of the admissibility constraints that introduces a dimensional parameter independent of cBI breaks at least one of BFS-consistent spectral scaling, structural non-injectivity (A2/ENI), or bounded admissibility closure (A3 A4). As an immediate corollary, dynamical fields carrying an independent dimensional coupling cannot be consistently coupled to the projection Π; this provides the structural underpinning for the exclusion of Reissner Nordstr\"om and Schwarzschild de Sitter geometries invoked in the companion paper Q6b. A stronger Level 2 statement, asserting full functional determination of all emergent scales, is beyond the scope of the present note and is identified as an open problem.