Compiles for Windows x64 via mingw-w64 and still compiles clean on POSIX (darwin/linux) — all Windows code is behind #ifdef _WIN32, POSIX path unchanged. - el_platform_win.h (new): winsock2 + auto WSAStartup, el_closesocket(), dlsym->GetProcAddress, popen/_popen, mkdir/_mkdir, setenv/_putenv_s, timegm/_mkgmtime, localtime_r/gmtime_r. Threading unchanged — mingw winpthreads supplies <pthread.h> + -lpthread. - el_runtime.c: include block guarded; 10 socket-close sites -> el_closesocket(); setsockopt arg4 cast; tm_zone guarded; exec_bg fork/exec -> CreateProcess. Part of feat/windows-port. Core-el change, for Will's review. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>