Regular Black Holes and EHT Shadow Constraints from First Principles in the SFT Emergent Framework

In this work, we present the formal derivation and phenomenological validation of massive, charged, and completely regular (non-singular) black holes strictly within the SFT Emergent Framework (SFT-EF). Within this unifying paradigm, the macroscopic spacetime metric is not a fundamental entity but emerges dynamically as a discrete lattice condensate from open Bosonic String Field Theory (SFT). To overcome the pathological limitations of purely static metrics in de Rham-Gabadadze-Tolley (dRGT) massive gravity, we adopt a time-dependent ansatz dynamically coupled to the Topological Volume Generation of the vacuum lattice. We demonstrate, both analytically and via high-resolution numerical simulations, that the topological strain stiffening of the vacuum substrate strictly arrests gravitational collapse: the Kretschmann invariant saturates safely in the ultraviolet (UV) regime, forming a dynamically stable Topologically Protected Core (remnant) completely free from the Boulware-Deser ghost. The macroscopic interaction of the emergent black hole with the dark sector is governed by an axial-vector charge Q₅ and modeled via Modified Maxwell (ModMax) non-linear electrodynamics. Crucially, unlike standard phenomenological models where the non-linearity is arbitrarily postulated, we analytically derive the ModMax parameter strictly from first principles (γMM ≈ 0.2) by computing the 1-loop vacuum polarization induced by heavy dark fermions confined within the spacetime condensate. Evaluated in the extended phase space, this emergent macroscopic SFT-EF configuration rigorously satisfies the First Law of Thermodynamics and the extended Smarr relation, exhibiting exotic van der Waals-type continuous phase transitions. To rigorously benchmark the model against contemporary astrophysical observables, we extract the exact null geodesic equations, mapping the photon sphere and the Black Hole Shadow radius. Ray-tracing analysis demonstrates that the ab-initio emergent 1-loop parameter γMM ≈ 0.2 provides a topological optical shield, generating a precise $3%-4%$ fractional geometric deviation in the shadow radius compared to the classical Schwarzschild limit. This exact theoretical prediction exquisitely satisfies the stringent instrumental confidence bounds established by the Event Horizon Telescope (EHT) collaboration for the supermassive black holes Sagittarius A* and M87*. Confrontation with this interferometric data allows us to extract a rigorous physical upper bound on the dark axial charge (Q₅ 0.8) and definitively confirms that the macroscopic kinematic impact of the graviton mass (mg) remains phenomenologically shielded at the horizon scale by the Vainshtein mechanism.