Two years after launching our Bluetooth-only iOS integration, we expanded Phone Link to support Microsoft Account (MSA) sign-in—unlocking advanced features like cross-device file sharing between iPhones and Windows PCs. I led the engineering effort to evolve our onboarding system into a hybrid model supporting both Bluetooth and MSA-based pairing. This was a critical-path dependency for launching file sharing, as highlighted in The Verge’s coverage. This onboarding flow introduced substantial UX and architectural complexity. I collaborated closely with product managers and designers to craft an experience that was flexible yet intuitive. Users could onboard via an App Clip-powered Bluetooth flow—requiring no app install—or opt into a full app experience for enhanced capabilities like file sharing via MSA. Full app onboarding also supported both methods from the outset, and the Phone Link Windows app had to accommodate all permutations seamlessly. My work enabled millions of users to get connected in seconds while providing a smooth path to richer features like file sharing—delivered on top of the robust foundation I built.