chore: checkpoint stable battle and eidolon progression

internal/common/persistent_lock_windows.go

@@ -0,0 +1,30 @@
+//go:build windows
+
+package common
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// LockFileEx's exclusive byte-range lock is released by Windows if either
+// process exits. The shared lock file coordinates SDK and game server saves.
+func lockPersistentFile() (func(), error) {
+	file, err := os.OpenFile("persistent.lock", os.O_CREATE|os.O_RDWR, 0600)
+	if err != nil {
+		return nil, err
+	}
+	dll := syscall.NewLazyDLL("kernel32.dll")
+	lock := dll.NewProc("LockFileEx")
+	unlock := dll.NewProc("UnlockFileEx")
+	overlapped := new(syscall.Overlapped)
+	const lockfileExclusiveLock = 2 // Win32 LOCKFILE_EXCLUSIVE_LOCK.
+	ok, _, callErr := lock.Call(file.Fd(), lockfileExclusiveLock, 0, 1, 0, uintptr(unsafe.Pointer(overlapped)))
+	if ok == 0 {
+		file.Close()
+		return nil, fmt.Errorf("lock persistent: %w", callErr)
+	}
+	return func() { unlock.Call(file.Fd(), 0, 1, 0, uintptr(unsafe.Pointer(overlapped))); file.Close() }, nil
+}