Developing wet adhesives integrating rapid interfacial adaptability and superior mechanical stability remains a long-standing hurdle. Existing liquid–liquid phase separation (LLPS)-based adhesives mainly exploit phase condensation for interfacial wetting, while the phase-separated domains rarely participate in active molecular reinforcement or adaptive mechanical regulation. Inspired by the hydration-regulated adaptive transition behavior of snail mucus, we herein constructed an adaptive coacervate adhesive through an phase-confined structure transformation and dual-network reinforcement. Through salt bridge-mediated phase separation between sodium thioctate and polycationic components, dense coacervate condensates are formed via synergistic salt-bridge interactions, providing highly confined microenvironments for realizing the ring-opening polymerization (ROP) of thioctic acid (TA). Consequently, the coacervate adhesive undergoes hydration-regulated reversible mechanical transition, featuring superior wet interfacial adaptability under the hydrated state and substantial dehydration-induced stiffening and cohesive reinforcement analogous to native snail mucus. Unlike conventional tissue sealants and sutures that often suffer from poor wet adaptability or rigid fixation, the adaptive coacervate system dynamically couples rapid interfacial wetting with dehydration-induced cohesive reinforcement (695.31 vs 24.7 N·m?2 of fibrin glue). This work establishes a universal biomimetic strategy for coupling confined molecular structural transformation with adaptive supramolecular mechanics toward designing adaptive biointerfaces.