feat: add deployment foundation and cross-device handoff

internal/state/lock_windows.go

@@ -0,0 +1,30 @@
+//go:build windows
+
+package state
+
+import (
+	"os"
+	"runtime"
+	"syscall"
+	"unsafe"
+)
+
+var lockFileEx = syscall.NewLazyDLL("kernel32.dll").NewProc("LockFileEx")
+
+func lockExclusive(f *os.File) error {
+	var overlapped syscall.Overlapped
+	// LOCKFILE_FAIL_IMMEDIATELY | LOCKFILE_EXCLUSIVE_LOCK, first byte only.
+	ok, _, err := lockFileEx.Call(f.Fd(), 3, 0, 1, 0, uintptr(unsafe.Pointer(&overlapped)))
+	runtime.KeepAlive(f)
+	if ok != 0 {
+		return nil
+	}
+	if err == syscall.Errno(33) {
+		return ErrBusy
+	}
+	return err
+}
+
+// Windows is a development platform. File.Sync is used, but Go does not provide
+// a portable directory fsync here. Do not claim Windows power-loss durability.
+func syncDirectory(*os.Root) error { return nil }