Digital transformation challenges the traditional foundations of national constitutionalism, creating a dialectical tension between adaptability and protectionism. The paper analyzes their interaction as two complementary strategies for ensuring the sustainability of the legal system: the first operates through a flexible interpretation of norms and institutional adaptation to digital challenges, the second — through the protection of the core of constitutional identity from normative diffusion. Through a comparative analysis of the legal practices of Germany, France, Italy, the United States, Russia, and China, the author identifies constitutional filtration as the key mechanism for synthesizing constitutional protectionism and adaptive constitutionalism. This mechanism consists of the selective and reflexive incorporation of external norms, including soft law norms and decisions of supranational courts, filtered through national constitutional values, procedural legitimacy, and the principle of proportionality. The effectiveness of modern legal systems hinges on their ability to engage in critical selection. German Identitätskontrolle (identity control), French constitutional review of the Avia law, Russian data localization requirements, and American regulatory pragmatism toward digital platforms each implement this mechanism through distinct approaches, yet they converge on a single outcome — the preservation of sovereignty without resorting to isolationism. The risks of legal relativism when using the terms «digital sovereignty» without judicial review and proportionality are highlighted. A model of reflexive legal immunity is proposed, where constitutional filtering becomes not just a technique, but a form of sustainable development of constitutional law in the era of algorithmic power. The results of the study substantiate the need for an interdisciplinary approach to digital constitutionalism, algorithmic justice, and platform sovereignty.