The Irreversibility Threshold: When Structural Recovery Becomes Impossible

La Profilée’s intervention logic (Paper 67) establishes that structural recovery from overload IR > 1 requires two phases: stabilization (ΔR) followed by restitution (ΔI, ΔF, ΔC). Paper 67 further establishes that intervention failure is structurally necessary when stabilization is delayed, restitution is incomplete, or the restitution sequence is violated within T_visible. The present paper derives the structural consequence of prolonged intervention failure: the Irreversibility Threshold. When effective integration capacity IK = F · I · C falls below a critical value I_crit, the system can no longer restore IK through its own restitution processes — even if transformation load R is reduced to zero. This follows from the self-referential character of restitution: the capacity required to rebuild I, F, and C is itself a function of current IK. Below I_crit, this self-referential process collapses. The paper establishes: (1) why I_crit exists as a structural necessity, (2) the distinction between reversible overload (IK > I_crit) and irreversible overload (IK ≤ I_crit), (3) what occurs structurally after I_crit is crossed, and (4) the relationship between I_crit and T_visible. Irreversibility is not a gradual endpoint. It is a structural threshold with a precise architectural meaning: the point at which the Frame–Module–Coupling architecture can no longer sustain the processes required for its own restoration.