Worked on the tailscale/tailscale repository to enhance DERP proxy connectivity by implementing port-aware dialing for DERP servers, ensuring that DERPPort is respected for both direct and proxied CONNECT paths. Used Go for backend development and network programming, introducing logic to dynamically select the correct port and provide reliable fallbacks. Extended the test suite to include comprehensive coverage of proxied port selection and end-to-end connectivity through real DERP servers and CONNECT proxies, while removing outdated tests to align with updated behavior. These improvements increased DERP reliability behind enterprise proxies and strengthened test coverage, reducing the risk of port-related regressions.