Recurrent Metastable Phase-Space Collapse in Quiet-Sun EUV Dynamics and Its Disruption by Energetic Perturbations

High-cadence Solar Dynamics Observatory (SDO/AIA) 171 Å observations reveal recurrent episodes of \textbf{phase-mediated attractor collapse}, in which the reconstructed EUV phase space transiently funnels into a near-one-dimensional stiff manifold during magnetically quiet conditions. These metastable states recur across multiple days, concentrating $>95\%$ of the variance onto a single stiff axis and exhibiting strongly negative angular Lyapunov proxies, indicative of deep but non-chaotic basin structure. During periods of energetic solar activity, including M- and X-class flares, the depth and frequency of these collapses are systematically suppressed, with the dynamics instead occupying a higher-dimensional, dynamically relaxed regime. This behavior is consistent with externally injected energy widening an otherwise narrow phase-locking channel, rather than inducing global chaotic divergence or destroying the underlying basin. To verify that the observed structure is not generated by cadence-locked or geometric instrumental effects, we quantify orbital contamination explicitly and introduce a global angular recurrence analysis that operates directly on local phase-turning angles without embedding, dimensional reduction, or amplitude-based distance metrics. Orbital phase explains only 1--5\% of variance along stiff axes and 2.37\% of the angular Lyapunov proxy, while phase-coherent recurrence persists across concatenated windows and multiple orbital cycles. These results demonstrate the existence of a robust, intrinsically organized \textbf{phase-mediated metastable regime} in quiet-Sun EUV dynamics that is disrupted—but not erased—by energetic perturbations. The framework isolates collective phase organization rather than physical degree reduction and is not presented as a flare-prediction diagnostic.