From Collinear Null Flow to Finite Black-Hole Interior Dynamics in Constrained Null Geometry

This work develops and numerically tests a black-hole sector of Constrained Null Geometry, beginning from a collinear null accumulation rather than from an assumed curved metric, stress-energy tensor, or pre-existing horizon. The construction follows a continuous geometric sequence from collinear null flow, through internal null-fiber fluctuations and first loss, to the emergence of a three-channel domain, global geometric response, curvature, and a trapped null boundary. A discrete escape-action operator is derived from the realized three-channel geometry and its birth-support structure. The numerical certificate produces a finite connected trapped region with a transparent exterior and strongly suppressed outward null admissibility. The weakest fully certified state remains far beyond the adopted numerical reporting level. The simulation is then continued beyond horizon formation without introducing new locks, additional mass, interior equations of state, phenomenological regularizations, or a separate horizon prescription. Across the tested continuation, the interior remains finite, compact, trapped, and dynamically reorganizing. No deconfinement, numerical singular runaway, or terminal static state is observed. The exterior global monopole flux remains constant across all tested interior snapshots. This shows that the internal reorganization does not produce a time-dependent monopole signal in the exterior. The black hole therefore remains locally one-way for outgoing null realization while preserving a constant global gravitational contribution. The empirical comparison is restricted to the exterior sector. Public M87* Event Horizon Telescope data support a coherent finite-band boundary-log ridge and the protected fixed cutoff at mode eight in the principal certificate windows. These results support the external protected-boundary geometry up to the horizon. They do not constitute a direct observation or reconstruction of the black-hole interior. Phase-specific, temporal-order, and direct raw-closure tests of the simulated interior do not pass. The finite dynamical interior beyond the horizon is therefore presented as a theoretical prediction of the same derived CNG operator chain, not as an empirically reconstructed interior. The principal result is divided explicitly into two parts: the exterior protected geometry through horizon formation is supported by the numerical and EHT boundary certificates; the finite dynamical interior beyond the horizon is a theoretical prediction of the same geometric construction. The accompanying supplementary archive contains supporting numerical tables, figures, decision files, checksums, and reproducibility material. It does not contain the manuscript PDF or manuscript LaTeX source.