diff --git a/CLAUDE.md b/CLAUDE.md
index e0bb6d3..c2a8dc6 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -10,7 +10,7 @@ C:\Users\98kim\sdk\go1.25.1\bin\go.exe build -ldflags="-H windowsgui -s -w" -o l
 
 ## Tech Stack
 
-- **Go** 단일 파일 (`main.go`)
+- **Go** 4파일 구조 (`main.go`, `ui.go`, `download.go`, `protocol.go`)
 - **Win32 API** — `user32.dll`, `gdi32.dll`, `comctl32.dll`, `uxtheme.dll`, `shell32.dll`
 - `golang.org/x/sys/windows` + `windows/registry`
 
@@ -21,13 +21,18 @@ C:\Users\98kim\sdk\go1.25.1\bin\go.exe build -ldflags="-H windowsgui -s -w" -o l
 
 ## Architecture
 
-모든 로직이 `main.go` 단일 파일에 있음:
+역할별 4파일 구조:
 
-- **`enableDPIAwareness()`** — `SetProcessDpiAwarenessContext(PER_MONITOR_AWARE_V2)` 호출. `main()` 첫 줄에서 실행.
+| 파일 | 담당 |
+|---|---|
+| `main.go` | 진입점(`main`), 단일 인스턴스, `handleURI`, version |
+| `ui.go` | Win32 DLL/proc 선언, WndProc, progress window, DPI, font, msgBox |
+| `download.go` | HTTP 클라이언트, 다운로드/추출/해시, `ensureGame`, `ensureLauncher` |
+| `protocol.go` | 상수, URI 프로토콜 등록/해제, `redeemTicket`, `fetchServerInfo` |
+
+주요 함수:
 - **`downloadWithProgress()`** — Win32 메시지 루프 직접 운영. 반드시 메인 고루틴에서 호출 (`runtime.LockOSThread`).
-- **`progressWndProc()`** — `WM_CTLCOLORSTATIC`으로 다크 테마 적용. `hBrushBg` 전역 변수 참조.
-- **`setProgress(text, pct)`** — 다운로드 고루틴에서 호출해 레이블 텍스트와 진행 막대 동시 업데이트.
-- **`fetchServerInfo()`** — `https://a301.api.tolelom.xyz/api/download/info` 조회.
+- **`fetchServerInfo()`** — 3회 재시도 (exponential backoff).
 - **`ensureGame()`** — `A301.exe` SHA256 해시 비교 후 불일치 시 재다운로드.
 
 ## UI Details
@@ -50,7 +55,7 @@ protocolName  = "a301"        // 기술 식별자
 - `install()` 시 런처를 `%LOCALAPPDATA%\A301\launcher.exe`로 복사 후 해당 경로를 레지스트리에 등록.
 - 게임 파일(`A301.exe` 등)도 `%LOCALAPPDATA%\A301\`에 설치됨.
 - 사용자가 원본 다운로드 파일을 삭제해도 프로토콜 핸들러가 정상 동작.
-- 토큰은 명령줄이 아닌 `A301_TOKEN` 환경변수로 게임에 전달.
+- 토큰은 커맨드라인(`-token`)과 `A301_TOKEN` 환경변수 양쪽으로 게임에 전달.
 
 ## Notes
 
diff --git a/download.go b/download.go
new file mode 100644
index 0000000..ccbb0d7
--- /dev/null
+++ b/download.go
@@ -0,0 +1,479 @@
+package main
+
+import (
+	"archive/zip"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync/atomic"
+	"time"
+)
+
+const maxDownloadSize = 2 << 30    // 2GB
+const maxExtractFileSize = 4 << 30 // 개별 파일 최대 4GB
+
+var downloadCancelled atomic.Bool
+
+var checkRedirect = func(req *http.Request, via []*http.Request) error {
+	if req.URL.Scheme != "https" && req.URL.Scheme != "http" {
+		return fmt.Errorf("허용되지 않는 리다이렉트 스킴: %s", req.URL.Scheme)
+	}
+	if len(via) >= 10 {
+		return fmt.Errorf("리다이렉트 횟수 초과")
+	}
+	return nil
+}
+
+// apiClient: 서버 정보 조회 등 짧은 요청용 (전체 120초 타임아웃)
+var apiClient = &http.Client{
+	Timeout:       120 * time.Second,
+	CheckRedirect: checkRedirect,
+}
+
+// downloadClient: 대용량 파일 다운로드용 (연결 30초 + 유휴 60초, 전체 타임아웃 없음)
+var downloadClient = &http.Client{
+	Transport: &http.Transport{
+		TLSHandshakeTimeout:   30 * time.Second,
+		ResponseHeaderTimeout: 30 * time.Second,
+		IdleConnTimeout:       60 * time.Second,
+	},
+	CheckRedirect: checkRedirect,
+}
+
+// doDownloadRequest sends a GET (with Range if a partial file exists).
+// If the server replies 416, it deletes the stale temp file and retries once.
+func doDownloadRequest(downloadURL, tmpPath string) (*http.Response, error) {
+	for attempt := 0; attempt < 2; attempt++ {
+		var resumeOffset int64
+		if fi, err := os.Stat(tmpPath); err == nil {
+			resumeOffset = fi.Size()
+		}
+
+		req, err := http.NewRequest("GET", downloadURL, nil)
+		if err != nil {
+			return nil, fmt.Errorf("다운로드 요청 생성 실패: %w", err)
+		}
+		if resumeOffset > 0 {
+			req.Header.Set("Range", fmt.Sprintf("bytes=%d-", resumeOffset))
+		}
+
+		resp, err := downloadClient.Do(req)
+		if err != nil {
+			return nil, fmt.Errorf("다운로드 연결 실패: %w", err)
+		}
+
+		if resp.StatusCode == http.StatusRequestedRangeNotSatisfiable {
+			resp.Body.Close()
+			os.Remove(tmpPath)
+			continue
+		}
+		return resp, nil
+	}
+	return nil, fmt.Errorf("다운로드 실패: 재시도 횟수 초과")
+}
+
+func doDownload(downloadURL, destDir string) error {
+	tmpPath := filepath.Join(os.TempDir(), "a301_game.zip")
+
+	resp, err := doDownloadRequest(downloadURL, tmpPath)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	var downloaded int64
+	var total int64
+	var tmpFile *os.File
+
+	var resumeOffset int64
+	if fi, statErr := os.Stat(tmpPath); statErr == nil {
+		resumeOffset = fi.Size()
+	}
+
+	switch resp.StatusCode {
+	case http.StatusPartialContent:
+		downloaded = resumeOffset
+		if resp.ContentLength > 0 {
+			total = resumeOffset + resp.ContentLength
+		}
+		tmpFile, err = os.OpenFile(tmpPath, os.O_WRONLY|os.O_APPEND, 0644)
+	case http.StatusOK:
+		if resp.ContentLength > 0 {
+			total = resp.ContentLength
+		}
+		tmpFile, err = os.Create(tmpPath)
+	default:
+		return fmt.Errorf("다운로드 실패 (HTTP %d)", resp.StatusCode)
+	}
+	if err != nil {
+		return fmt.Errorf("임시 파일 열기 실패: %w", err)
+	}
+
+	if total > maxDownloadSize {
+		tmpFile.Close()
+		os.Remove(tmpPath)
+		return fmt.Errorf("파일이 너무 큽니다 (%d bytes)", total)
+	}
+
+	buf := make([]byte, 32*1024)
+
+	var lastSpeedUpdate time.Time
+	var lastBytes int64
+	var speedBytesPerSec float64
+
+	for {
+		if downloadCancelled.Load() {
+			tmpFile.Close()
+			return fmt.Errorf("다운로드가 취소되었습니다")
+		}
+		n, err := resp.Body.Read(buf)
+		if n > 0 {
+			if _, werr := tmpFile.Write(buf[:n]); werr != nil {
+				tmpFile.Close()
+				return fmt.Errorf("파일 쓰기 실패: %w", werr)
+			}
+			downloaded += int64(n)
+			if downloaded > maxDownloadSize {
+				tmpFile.Close()
+				os.Remove(tmpPath)
+				return fmt.Errorf("다운로드 크기가 제한을 초과했습니다")
+			}
+
+			now := time.Now()
+			if now.Sub(lastSpeedUpdate) >= 500*time.Millisecond {
+				elapsed := now.Sub(lastSpeedUpdate).Seconds()
+				if elapsed > 0 {
+					speedBytesPerSec = float64(downloaded-lastBytes) / elapsed
+				}
+				lastBytes = downloaded
+				lastSpeedUpdate = now
+			}
+
+			if total > 0 {
+				pct := int(downloaded * 100 / total)
+				if pct > 100 {
+					pct = 100
+				}
+
+				speedMB := speedBytesPerSec / 1024 / 1024
+				text := fmt.Sprintf("다운로드 중... %d%%  (%.1f MB/s)", pct, speedMB)
+				if speedBytesPerSec > 0 {
+					remaining := float64(total-downloaded) / speedBytesPerSec
+					if remaining < 60 {
+						text = fmt.Sprintf("다운로드 중... %d%%  (%.1f MB/s, %d초 남음)", pct, speedMB, int(remaining))
+					} else {
+						text = fmt.Sprintf("다운로드 중... %d%%  (%.1f MB/s, %d분 남음)", pct, speedMB, int(remaining/60))
+					}
+				}
+				setProgress(text, pct)
+			}
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			tmpFile.Close()
+			return fmt.Errorf("다운로드 중 오류: %w", err)
+		}
+	}
+	tmpFile.Close()
+	defer os.Remove(tmpPath)
+
+	setProgress("압축을 해제하는 중...", -1)
+
+	tmpExtractDir, err := os.MkdirTemp("", "a301_extract_")
+	if err != nil {
+		return fmt.Errorf("임시 추출 디렉토리 생성 실패: %w", err)
+	}
+
+	if err := extractZip(tmpPath, tmpExtractDir); err != nil {
+		os.RemoveAll(tmpExtractDir)
+		return err
+	}
+
+	if err := moveContents(tmpExtractDir, destDir); err != nil {
+		os.RemoveAll(tmpExtractDir)
+		return fmt.Errorf("파일 이동 실패: %w", err)
+	}
+	os.RemoveAll(tmpExtractDir)
+	return nil
+}
+
+func extractZip(zipPath, destDir string) error {
+	r, err := zip.OpenReader(zipPath)
+	if err != nil {
+		return fmt.Errorf("zip 열기 실패: %w", err)
+	}
+	defer r.Close()
+
+	selfName := strings.ToLower(filepath.Base(os.Args[0]))
+
+	for _, f := range r.File {
+		clean := filepath.ToSlash(f.Name)
+		parts := strings.SplitN(clean, "/", 2)
+		var rel string
+		if len(parts) == 2 && parts[1] != "" {
+			rel = parts[1]
+		} else if len(parts) == 1 && !strings.Contains(clean, "/") && parts[0] != "" {
+			rel = parts[0]
+		} else {
+			continue
+		}
+
+		if filepath.IsAbs(rel) {
+			return fmt.Errorf("잘못된 zip 경로 (절대 경로): %s", rel)
+		}
+		if strings.Contains(rel, ":") {
+			return fmt.Errorf("잘못된 zip 경로 (ADS): %s", rel)
+		}
+
+		if strings.ToLower(filepath.Base(rel)) == selfName {
+			continue
+		}
+
+		dest := filepath.Join(destDir, filepath.FromSlash(rel))
+
+		cleanDest := filepath.Clean(dest)
+		cleanBase := filepath.Clean(destDir) + string(os.PathSeparator)
+		if !strings.HasPrefix(cleanDest, cleanBase) && cleanDest != filepath.Clean(destDir) {
+			return fmt.Errorf("잘못된 zip 경로: %s", rel)
+		}
+
+		if f.FileInfo().Mode()&os.ModeSymlink != 0 {
+			continue
+		}
+
+		if f.FileInfo().IsDir() {
+			os.MkdirAll(dest, 0755)
+			continue
+		}
+
+		if err := os.MkdirAll(filepath.Dir(dest), 0755); err != nil {
+			return err
+		}
+
+		rc, err := f.Open()
+		if err != nil {
+			return err
+		}
+		out, err := os.Create(dest)
+		if err != nil {
+			rc.Close()
+			return err
+		}
+		_, err = io.Copy(out, io.LimitReader(rc, maxExtractFileSize))
+		closeErr := out.Close()
+		rc.Close()
+		if err != nil {
+			return err
+		}
+		if closeErr != nil {
+			return fmt.Errorf("파일 닫기 실패: %w", closeErr)
+		}
+	}
+	return nil
+}
+
+func moveContents(srcDir, dstDir string) error {
+	entries, err := os.ReadDir(srcDir)
+	if err != nil {
+		return err
+	}
+	for _, e := range entries {
+		src := filepath.Join(srcDir, e.Name())
+		dst := filepath.Join(dstDir, e.Name())
+		if e.IsDir() {
+			if err := os.MkdirAll(dst, 0755); err != nil {
+				return err
+			}
+			if err := moveContents(src, dst); err != nil {
+				return err
+			}
+		} else {
+			os.Remove(dst)
+			if err := os.Rename(src, dst); err != nil {
+				if err := copyFile(src, dst); err != nil {
+					os.Remove(dst)
+					return err
+				}
+				os.Remove(src)
+			}
+		}
+	}
+	return nil
+}
+
+func copyFile(src, dst string) error {
+	in, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+	out, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	if _, err = io.Copy(out, in); err != nil {
+		out.Close()
+		return err
+	}
+	return out.Close()
+}
+
+func hashFile(path string) (string, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	h := sha256.New()
+	if _, err := io.Copy(h, f); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}
+
+func ensureGame(gameDir, gamePath string, serverInfo *downloadInfo) error {
+	if serverInfo.FileHash == "" {
+		return fmt.Errorf("서버에서 유효한 파일 정보를 받지 못했습니다")
+	}
+
+	needsDownload := false
+
+	if _, err := os.Stat(gamePath); os.IsNotExist(err) {
+		needsDownload = true
+	} else if err != nil {
+		return fmt.Errorf("게임 파일 확인 실패: %w", err)
+	} else {
+		localHash, err := hashFile(gamePath)
+		if err != nil {
+			return fmt.Errorf("파일 검증 실패: %w", err)
+		}
+		if !strings.EqualFold(localHash, serverInfo.FileHash) {
+			needsDownload = true
+		}
+	}
+
+	if needsDownload {
+		if serverInfo.URL == "" {
+			return fmt.Errorf("다운로드 URL이 없습니다")
+		}
+		u, err := url.Parse(serverInfo.URL)
+		if err != nil || (u.Scheme != "https" && u.Scheme != "http") {
+			return fmt.Errorf("유효하지 않은 다운로드 URL")
+		}
+		if err := downloadWithProgress(serverInfo.URL, gameDir); err != nil {
+			return fmt.Errorf("게임 설치 실패: %w", err)
+		}
+		if serverInfo.FileHash != "" {
+			newHash, err := hashFile(gamePath)
+			if err != nil {
+				return fmt.Errorf("다운로드 후 파일 검증 실패: %w", err)
+			}
+			if !strings.EqualFold(newHash, serverInfo.FileHash) {
+				os.Remove(gamePath)
+				return fmt.Errorf("다운로드된 파일의 해시가 일치하지 않습니다 (파일이 손상되었을 수 있습니다)")
+			}
+		}
+	}
+
+	return nil
+}
+
+// downloadFile downloads a file from url to destPath using apiClient.
+func downloadFile(dlURL, destPath string) error {
+	resp, err := apiClient.Get(dlURL)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("HTTP %d", resp.StatusCode)
+	}
+	f, err := os.Create(destPath)
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(f, io.LimitReader(resp.Body, maxDownloadSize))
+	if closeErr := f.Close(); closeErr != nil && err == nil {
+		err = closeErr
+	}
+	return err
+}
+
+// ensureLauncher checks if the installed launcher is up-to-date and replaces it if not.
+func ensureLauncher(serverInfo *downloadInfo) (updated bool, err error) {
+	if serverInfo.LauncherHash == "" {
+		return false, nil
+	}
+
+	installedPath, err := launcherPath()
+	if err != nil {
+		return false, nil
+	}
+
+	localHash, err := hashFile(installedPath)
+	if err != nil {
+		return false, nil
+	}
+
+	if strings.EqualFold(localHash, serverInfo.LauncherHash) {
+		return false, nil
+	}
+
+	dlURL := serverInfo.LauncherURL
+	if dlURL == "" {
+		return false, nil
+	}
+
+	newPath := installedPath + ".new"
+	if err := downloadFile(dlURL, newPath); err != nil {
+		os.Remove(newPath)
+		return false, fmt.Errorf("런처 업데이트 다운로드 실패: %w", err)
+	}
+
+	newHash, err := hashFile(newPath)
+	if err != nil {
+		os.Remove(newPath)
+		return false, fmt.Errorf("런처 검증 실패: %w", err)
+	}
+	if !strings.EqualFold(newHash, serverInfo.LauncherHash) {
+		os.Remove(newPath)
+		return false, fmt.Errorf("런처 해시 불일치")
+	}
+
+	oldPath := installedPath + ".old"
+	os.Remove(oldPath)
+	if err := os.Rename(installedPath, oldPath); err != nil {
+		os.Remove(newPath)
+		return false, fmt.Errorf("런처 교체 실패: %w", err)
+	}
+	if err := os.Rename(newPath, installedPath); err != nil {
+		if restoreErr := os.Rename(oldPath, installedPath); restoreErr != nil {
+			return false, fmt.Errorf("런처 교체 실패 및 복원 불가: %w (원인: %v)", restoreErr, err)
+		}
+		return false, fmt.Errorf("런처 교체 실패: %w", err)
+	}
+
+	return true, nil
+}
+
+// cleanupOldFiles removes .old and .new leftover files from previous launcher updates.
+func cleanupOldFiles(dir string) {
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return
+	}
+	for _, e := range entries {
+		name := e.Name()
+		if strings.HasSuffix(name, ".old") || strings.HasSuffix(name, ".new") {
+			os.Remove(filepath.Join(dir, name))
+		}
+	}
+}
diff --git a/main.go b/main.go
index ced4cfe..fdf5751 100644
--- a/main.go
+++ b/main.go
@@ -1,1087 +1,17 @@
 package main
 
 import (
-	"archive/zip"
-	"crypto/sha256"
-	"encoding/hex"
-	"encoding/json"
-	"errors"
 	"fmt"
-	"io"
-	"net/http"
 	"net/url"
 	"os"
 	"os/exec"
 	"path/filepath"
-	"runtime"
 	"strings"
-	"sync/atomic"
-	"syscall"
-	"time"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-	"golang.org/x/sys/windows/registry"
 )
 
 // version is set at build time via -ldflags "-X main.version=x.y.z"
 var version = "dev"
 
-const (
-	protocolName     = "a301"
-	gameExeName      = "A301.exe"
-	serverInfoURL    = "https://a301.api.tolelom.xyz/api/download/info"
-	redeemTicketURL  = "https://a301.api.tolelom.xyz/api/auth/redeem-ticket"
-)
-
-const maxDownloadSize = 2 << 30 // 2GB
-const maxExtractFileSize = 4 << 30 // 개별 파일 최대 4GB
-
-var checkRedirect = func(req *http.Request, via []*http.Request) error {
-	if req.URL.Scheme != "https" && req.URL.Scheme != "http" {
-		return fmt.Errorf("허용되지 않는 리다이렉트 스킴: %s", req.URL.Scheme)
-	}
-	if len(via) >= 10 {
-		return fmt.Errorf("리다이렉트 횟수 초과")
-	}
-	return nil
-}
-
-// apiClient: 서버 정보 조회 등 짧은 요청용 (전체 120초 타임아웃)
-var apiClient = &http.Client{
-	Timeout:       120 * time.Second,
-	CheckRedirect: checkRedirect,
-}
-
-// downloadClient: 대용량 파일 다운로드용 (연결 30초 + 유휴 60초, 전체 타임아웃 없음)
-var downloadClient = &http.Client{
-	Transport: &http.Transport{
-		TLSHandshakeTimeout:   30 * time.Second,
-		ResponseHeaderTimeout: 30 * time.Second,
-		IdleConnTimeout:       60 * time.Second,
-	},
-	CheckRedirect: checkRedirect,
-}
-
-// Win32 constants
-const (
-	wmDestroy        uint32 = 0x0002
-	wmClose          uint32 = 0x0010
-	wmSetFont        uint32 = 0x0030
-	wmSetText        uint32 = 0x000C
-	wmCtlColorStatic uint32 = 0x0138
-	wmAppDone        uint32 = 0x8001
-
-	wsPopup   uintptr = 0x80000000
-	wsCaption uintptr = 0x00C00000
-	wsSysMenu uintptr = 0x00080000
-	wsChild   uintptr = 0x40000000
-	wsVisible uintptr = 0x10000000
-	ssCenter  uintptr = 0x00000001
-
-	pbsSmooth      uintptr = 0x01
-	pbmSetRange32  uint32  = 0x0406
-	pbmSetPos      uint32  = 0x0402
-	pbmSetBarColor uint32  = 0x0409
-	pbmSetBkColor  uint32  = 0x2001
-
-	setBkModeTransparent = 1
-
-	swShow     = 5
-	smCxScreen = 0
-	smCyScreen = 1
-
-	mbOK    uintptr = 0x00000000
-	mbInfo  uintptr = 0x00000040
-	mbError uintptr = 0x00000010
-	mbYesNo uintptr = 0x00000004
-	mbQ     uintptr = 0x00000020
-	idYes           = 6
-
-	iccProgressClass uint32 = 0x00000020
-)
-
-// rgb builds a COLORREF from R, G, B components.
-func rgb(r, g, b uint8) uintptr {
-	return uintptr(r) | (uintptr(g) << 8) | (uintptr(b) << 16)
-}
-
-// 웹사이트 색상과 동일한 팔레트
-var (
-	colorBg         = rgb(46, 44, 47)   // #2E2C2F
-	colorText       = rgb(200, 200, 200) // 밝은 회색
-	colorAccent     = rgb(186, 205, 176) // #BACDB0
-	colorProgressBg = rgb(65, 63, 67)   // bg보다 약간 밝은 색
-)
-
-var (
-	user32   = windows.NewLazySystemDLL("user32.dll")
-	kernel32 = windows.NewLazySystemDLL("kernel32.dll")
-	gdi32    = windows.NewLazySystemDLL("gdi32.dll")
-	comctl32 = windows.NewLazySystemDLL("comctl32.dll")
-	uxtheme  = windows.NewLazySystemDLL("uxtheme.dll")
-
-	messageBoxWProc                   = user32.NewProc("MessageBoxW")
-	registerClassExWProc              = user32.NewProc("RegisterClassExW")
-	createWindowExWProc               = user32.NewProc("CreateWindowExW")
-	showWindowProc                    = user32.NewProc("ShowWindow")
-	updateWindowProc                  = user32.NewProc("UpdateWindow")
-	getMessageWProc                   = user32.NewProc("GetMessageW")
-	translateMsgProc                  = user32.NewProc("TranslateMessage")
-	dispatchMsgWProc                  = user32.NewProc("DispatchMessageW")
-	sendMessageWProc                  = user32.NewProc("SendMessageW")
-	postMessageWProc                  = user32.NewProc("PostMessageW")
-	defWindowProcWProc                = user32.NewProc("DefWindowProcW")
-	destroyWindowProc                 = user32.NewProc("DestroyWindow")
-	postQuitMsgProc                   = user32.NewProc("PostQuitMessage")
-	getSystemMetricsProc              = user32.NewProc("GetSystemMetrics")
-	getDpiForSystemProc               = user32.NewProc("GetDpiForSystem")
-	setProcessDpiAwarenessContextProc = user32.NewProc("SetProcessDpiAwarenessContext")
-	findWindowWProc                   = user32.NewProc("FindWindowW")
-	setForegroundWindowProc           = user32.NewProc("SetForegroundWindow")
-	createMutexWProc                  = kernel32.NewProc("CreateMutexW")
-	getModuleHandleWProc              = kernel32.NewProc("GetModuleHandleW")
-	createFontIndirectWProc           = gdi32.NewProc("CreateFontIndirectW")
-	createSolidBrushProc              = gdi32.NewProc("CreateSolidBrush")
-	setTextColorProc                  = gdi32.NewProc("SetTextColor")
-	setBkModeProc                     = gdi32.NewProc("SetBkMode")
-	deleteObjectProc                  = gdi32.NewProc("DeleteObject")
-	initCommonControlsExProc          = comctl32.NewProc("InitCommonControlsEx")
-	setWindowThemeProc                = uxtheme.NewProc("SetWindowTheme")
-
-	wndProcCb         uintptr
-	titleLabelHwnd    uintptr
-	progressLabelHwnd uintptr
-	progressBarHwnd   uintptr
-	hBrushBg          uintptr
-	downloadCancelled atomic.Bool
-)
-
-type wndClassExW struct {
-	cbSize        uint32
-	style         uint32
-	lpfnWndProc   uintptr
-	cbClsExtra    int32
-	cbWndExtra    int32
-	hInstance     uintptr
-	hIcon         uintptr
-	hCursor       uintptr
-	hbrBackground uintptr
-	lpszMenuName  *uint16
-	lpszClassName *uint16
-	hIconSm       uintptr
-}
-
-type msgW struct {
-	hwnd    uintptr
-	message uint32
-	wParam  uintptr
-	lParam  uintptr
-	time    uint32
-	ptX     int32
-	ptY     int32
-}
-
-type initCommonControlsExS struct {
-	dwSize uint32
-	dwICC  uint32
-}
-
-type logFontW struct {
-	lfHeight         int32
-	lfWidth          int32
-	lfEscapement     int32
-	lfOrientation    int32
-	lfWeight         int32
-	lfItalic         byte
-	lfUnderline      byte
-	lfStrikeOut      byte
-	lfCharSet        byte
-	lfOutPrecision   byte
-	lfClipPrecision  byte
-	lfQuality        byte
-	lfPitchAndFamily byte
-	lfFaceName       [32]uint16
-}
-
-func init() {
-	wndProcCb = syscall.NewCallback(progressWndProc)
-}
-
-// ── DPI helpers ──────────────────────────────────────────────────────────────
-
-func enableDPIAwareness() {
-	// DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 = -4 (Windows 10 1703+)
-	setProcessDpiAwarenessContextProc.Call(^uintptr(3))
-}
-
-func getSystemDPI() uint32 {
-	dpi, _, _ := getDpiForSystemProc.Call()
-	if dpi == 0 {
-		return 96
-	}
-	return uint32(dpi)
-}
-
-// dpiScale scales a base-96-DPI pixel value to the system DPI.
-// Uses floating-point to avoid precision loss on non-standard DPI values.
-func dpiScale(px int, dpi uint32) uintptr {
-	return uintptr(int(float64(px)*float64(dpi)/96.0 + 0.5))
-}
-
-// ── Font helpers ─────────────────────────────────────────────────────────────
-
-func createUIFont(pointSize int, dpi uint32, bold bool) uintptr {
-	weight := int32(400) // FW_NORMAL
-	if bold {
-		weight = 700 // FW_BOLD
-	}
-	lf := logFontW{
-		lfHeight:  -int32(pointSize) * int32(dpi) / 72,
-		lfWeight:  weight,
-		lfCharSet: 1, // DEFAULT_CHARSET
-		lfQuality: 5, // CLEARTYPE_QUALITY
-	}
-	face, _ := windows.UTF16FromString("Segoe UI")
-	copy(lf.lfFaceName[:], face)
-	font, _, _ := createFontIndirectWProc.Call(uintptr(unsafe.Pointer(&lf)))
-	// font가 0이면 시스템 기본 폰트가 사용됨 (WM_SETFONT에 0 전달 시 기본값)
-	return font
-}
-
-// ── Common controls ──────────────────────────────────────────────────────────
-
-func initCommonControls() {
-	icc := initCommonControlsExS{
-		dwSize: uint32(unsafe.Sizeof(initCommonControlsExS{})),
-		dwICC:  iccProgressClass,
-	}
-	initCommonControlsExProc.Call(uintptr(unsafe.Pointer(&icc)))
-}
-
-// ── Win32 helpers ────────────────────────────────────────────────────────────
-
-func msgBox(title, text string, flags uintptr) int {
-	t, err := windows.UTF16PtrFromString(title)
-	if err != nil {
-		return 0
-	}
-	m, err := windows.UTF16PtrFromString(text)
-	if err != nil {
-		return 0
-	}
-	ret, _, _ := messageBoxWProc.Call(0, uintptr(unsafe.Pointer(m)), uintptr(unsafe.Pointer(t)), flags)
-	return int(ret)
-}
-
-// ── Progress window ──────────────────────────────────────────────────────────
-
-func progressWndProc(hwnd, uMsg, wParam, lParam uintptr) uintptr {
-	switch uint32(uMsg) {
-	case wmClose:
-		ret := msgBox("One of the plans 런처", "다운로드를 취소하시겠습니까?", mbYesNo|mbQ)
-		if ret == idYes {
-			downloadCancelled.Store(true)
-			destroyWindowProc.Call(hwnd)
-		}
-		return 0
-	case wmDestroy:
-		postQuitMsgProc.Call(0)
-		return 0
-	case wmAppDone:
-		destroyWindowProc.Call(hwnd)
-		return 0
-	case wmCtlColorStatic:
-		// 다크 테마: 배경 브러시 + 텍스트 색 지정
-		hdc := wParam
-		setBkModeProc.Call(hdc, setBkModeTransparent)
-		if lParam == titleLabelHwnd {
-			setTextColorProc.Call(hdc, colorAccent)
-		} else {
-			setTextColorProc.Call(hdc, colorText)
-		}
-		return hBrushBg
-	}
-	ret, _, _ := defWindowProcWProc.Call(hwnd, uMsg, wParam, lParam)
-	return ret
-}
-
-func setProgress(text string, pct int) {
-	if text != "" {
-		t, err := windows.UTF16PtrFromString(text)
-		if err == nil {
-			sendMessageWProc.Call(progressLabelHwnd, uintptr(wmSetText), 0, uintptr(unsafe.Pointer(t)))
-		}
-	}
-	if pct >= 0 {
-		sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetPos), uintptr(pct), 0)
-	}
-}
-
-// downloadWithProgress shows a DPI-aware dark-themed progress window and downloads+extracts the zip.
-// Must be called from the main goroutine (Win32 message loop requirement).
-func downloadWithProgress(downloadURL, destDir string) error {
-	runtime.LockOSThread()
-	defer runtime.UnlockOSThread()
-
-	initCommonControls()
-	dpi := getSystemDPI()
-	s := func(px int) uintptr { return dpiScale(px, dpi) }
-
-	// 배경 브러시 생성 (window proc에서도 사용)
-	hBrushBg, _, _ = createSolidBrushProc.Call(colorBg)
-	defer deleteObjectProc.Call(hBrushBg)
-
-	hInstance, _, _ := getModuleHandleWProc.Call(0)
-
-	className, _ := windows.UTF16PtrFromString("A301Progress")
-	wc := wndClassExW{
-		cbSize:        uint32(unsafe.Sizeof(wndClassExW{})),
-		lpfnWndProc:   wndProcCb,
-		hInstance:     hInstance,
-		lpszClassName: className,
-		hbrBackground: hBrushBg,
-	}
-	atom, _, _ := registerClassExWProc.Call(uintptr(unsafe.Pointer(&wc)))
-	if atom == 0 {
-		return fmt.Errorf("윈도우 클래스 등록 실패")
-	}
-
-	screenW, _, _ := getSystemMetricsProc.Call(smCxScreen)
-	screenH, _, _ := getSystemMetricsProc.Call(smCyScreen)
-	winW := s(440)
-	winH := s(152)
-	x := (screenW - winW) / 2
-	y := (screenH - winH) / 2
-
-	// 창 타이틀은 비워서 타이틀바를 최소화
-	titleStr, _ := windows.UTF16PtrFromString("One of the plans 런처")
-	hwnd, _, _ := createWindowExWProc.Call(
-		0,
-		uintptr(unsafe.Pointer(className)),
-		uintptr(unsafe.Pointer(titleStr)),
-		wsPopup|wsCaption|wsSysMenu|wsVisible,
-		x, y, winW, winH,
-		0, 0, hInstance, 0,
-	)
-	if hwnd == 0 {
-		return fmt.Errorf("다운로드 창 생성 실패")
-	}
-
-	titleFont := createUIFont(13, dpi, true)
-	defer deleteObjectProc.Call(titleFont)
-	statusFont := createUIFont(9, dpi, false)
-	defer deleteObjectProc.Call(statusFont)
-
-	staticClass, _ := windows.UTF16PtrFromString("STATIC")
-
-	// ── "A301" 타이틀 레이블 ──
-	// 클라이언트 영역 레이아웃 (base 96 DPI):
-	//   y=14  h=28  → "A301" 타이틀 (13pt bold, 강조색)
-	//   y=52  h=20  → 상태 텍스트   (9pt, 밝은 회색)
-	//   y=82  h=18  → 진행 막대
-	titleText, _ := windows.UTF16PtrFromString("One of the plans")
-	titleLabelHwnd, _, _ = createWindowExWProc.Call(
-		0,
-		uintptr(unsafe.Pointer(staticClass)),
-		uintptr(unsafe.Pointer(titleText)),
-		wsChild|wsVisible|ssCenter,
-		s(20), s(14), winW-s(40), s(28),
-		hwnd, 0, hInstance, 0,
-	)
-	sendMessageWProc.Call(titleLabelHwnd, uintptr(wmSetFont), titleFont, 1)
-
-	// ── 상태 레이블 ──
-	initText, _ := windows.UTF16PtrFromString("게임 파일을 다운로드하는 중...")
-	progressLabelHwnd, _, _ = createWindowExWProc.Call(
-		0,
-		uintptr(unsafe.Pointer(staticClass)),
-		uintptr(unsafe.Pointer(initText)),
-		wsChild|wsVisible|ssCenter,
-		s(20), s(52), winW-s(40), s(20),
-		hwnd, 0, hInstance, 0,
-	)
-	sendMessageWProc.Call(progressLabelHwnd, uintptr(wmSetFont), statusFont, 1)
-
-	// ── 진행 막대 ──
-	progressClass, _ := windows.UTF16PtrFromString("msctls_progress32")
-	progressBarHwnd, _, _ = createWindowExWProc.Call(
-		0,
-		uintptr(unsafe.Pointer(progressClass)),
-		0,
-		wsChild|wsVisible|pbsSmooth,
-		s(20), s(82), winW-s(40), s(18),
-		hwnd, 0, hInstance, 0,
-	)
-	sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetRange32), 0, 100)
-
-	// 비주얼 스타일 비활성화 → PBM_SETBARCOLOR/PBM_SETBKCOLOR 적용 가능
-	empty, _ := windows.UTF16PtrFromString("")
-	setWindowThemeProc.Call(progressBarHwnd, uintptr(unsafe.Pointer(empty)), uintptr(unsafe.Pointer(empty)))
-	sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetBarColor), 0, colorAccent)
-	sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetBkColor), 0, colorProgressBg)
-
-	showWindowProc.Call(hwnd, swShow)
-	updateWindowProc.Call(hwnd)
-
-	downloadCancelled.Store(false)
-
-	errCh := make(chan error, 1)
-	go func() {
-		errCh <- doDownload(downloadURL, destDir)
-		// 윈도우가 이미 파괴된 경우(취소) PostMessage는 무시됨
-		postMessageWProc.Call(hwnd, uintptr(wmAppDone), 0, 0)
-	}()
-
-	var m msgW
-	for {
-		ret, _, _ := getMessageWProc.Call(uintptr(unsafe.Pointer(&m)), 0, 0, 0)
-		if ret == 0 || ret == ^uintptr(0) {
-			break
-		}
-		translateMsgProc.Call(uintptr(unsafe.Pointer(&m)))
-		dispatchMsgWProc.Call(uintptr(unsafe.Pointer(&m)))
-	}
-
-	return <-errCh
-}
-
-// doDownloadRequest sends a GET (with Range if a partial file exists).
-// If the server replies 416, it deletes the stale temp file and retries once.
-func doDownloadRequest(downloadURL, tmpPath string) (*http.Response, error) {
-	for attempt := 0; attempt < 2; attempt++ {
-		var resumeOffset int64
-		if fi, err := os.Stat(tmpPath); err == nil {
-			resumeOffset = fi.Size()
-		}
-
-		req, err := http.NewRequest("GET", downloadURL, nil)
-		if err != nil {
-			return nil, fmt.Errorf("다운로드 요청 생성 실패: %w", err)
-		}
-		if resumeOffset > 0 {
-			req.Header.Set("Range", fmt.Sprintf("bytes=%d-", resumeOffset))
-		}
-
-		resp, err := downloadClient.Do(req)
-		if err != nil {
-			return nil, fmt.Errorf("다운로드 연결 실패: %w", err)
-		}
-
-		if resp.StatusCode == http.StatusRequestedRangeNotSatisfiable {
-			resp.Body.Close()
-			os.Remove(tmpPath)
-			continue // 임시 파일 삭제 후 처음부터 재시도
-		}
-		return resp, nil
-	}
-	return nil, fmt.Errorf("다운로드 실패: 재시도 횟수 초과")
-}
-
-func doDownload(downloadURL, destDir string) error {
-	tmpPath := filepath.Join(os.TempDir(), "a301_game.zip")
-
-	resp, err := doDownloadRequest(downloadURL, tmpPath)
-	if err != nil {
-		return err
-	}
-	defer resp.Body.Close()
-
-	var downloaded int64
-	var total int64
-	var tmpFile *os.File
-
-	// 이어받기: 기존 임시 파일 크기 확인
-	var resumeOffset int64
-	if fi, statErr := os.Stat(tmpPath); statErr == nil {
-		resumeOffset = fi.Size()
-	}
-
-	switch resp.StatusCode {
-	case http.StatusPartialContent:
-		// 서버가 Range 요청 수락 → 이어받기
-		downloaded = resumeOffset
-		if resp.ContentLength > 0 {
-			total = resumeOffset + resp.ContentLength
-		}
-		tmpFile, err = os.OpenFile(tmpPath, os.O_WRONLY|os.O_APPEND, 0644)
-	case http.StatusOK:
-		// 서버가 Range 미지원이거나 파일이 변경됨 → 처음부터
-		if resp.ContentLength > 0 {
-			total = resp.ContentLength
-		}
-		tmpFile, err = os.Create(tmpPath)
-	default:
-		return fmt.Errorf("다운로드 실패 (HTTP %d)", resp.StatusCode)
-	}
-	if err != nil {
-		return fmt.Errorf("임시 파일 열기 실패: %w", err)
-	}
-
-	if total > maxDownloadSize {
-		tmpFile.Close()
-		os.Remove(tmpPath)
-		return fmt.Errorf("파일이 너무 큽니다 (%d bytes)", total)
-	}
-
-	buf := make([]byte, 32*1024)
-
-	var lastSpeedUpdate time.Time
-	var lastBytes int64
-	var speedBytesPerSec float64
-
-	for {
-		if downloadCancelled.Load() {
-			tmpFile.Close()
-			// 취소 시 임시 파일 유지 (이어받기 가능)
-			return fmt.Errorf("다운로드가 취소되었습니다")
-		}
-		n, err := resp.Body.Read(buf)
-		if n > 0 {
-			if _, werr := tmpFile.Write(buf[:n]); werr != nil {
-				tmpFile.Close()
-				return fmt.Errorf("파일 쓰기 실패: %w", werr)
-			}
-			downloaded += int64(n)
-			if downloaded > maxDownloadSize {
-				tmpFile.Close()
-				os.Remove(tmpPath)
-				return fmt.Errorf("다운로드 크기가 제한을 초과했습니다")
-			}
-
-			now := time.Now()
-			if now.Sub(lastSpeedUpdate) >= 500*time.Millisecond {
-				elapsed := now.Sub(lastSpeedUpdate).Seconds()
-				if elapsed > 0 {
-					speedBytesPerSec = float64(downloaded-lastBytes) / elapsed
-				}
-				lastBytes = downloaded
-				lastSpeedUpdate = now
-			}
-
-			if total > 0 {
-				pct := int(downloaded * 100 / total)
-				if pct > 100 {
-					pct = 100
-				}
-
-				speedMB := speedBytesPerSec / 1024 / 1024
-				text := fmt.Sprintf("다운로드 중... %d%%  (%.1f MB/s)", pct, speedMB)
-				if speedBytesPerSec > 0 {
-					remaining := float64(total-downloaded) / speedBytesPerSec
-					if remaining < 60 {
-						text = fmt.Sprintf("다운로드 중... %d%%  (%.1f MB/s, %d초 남음)", pct, speedMB, int(remaining))
-					} else {
-						text = fmt.Sprintf("다운로드 중... %d%%  (%.1f MB/s, %d분 남음)", pct, speedMB, int(remaining/60))
-					}
-				}
-				setProgress(text, pct)
-			}
-		}
-		if err == io.EOF {
-			break
-		}
-		if err != nil {
-			tmpFile.Close()
-			// 네트워크 오류 시 임시 파일 유지 (이어받기 가능)
-			return fmt.Errorf("다운로드 중 오류: %w", err)
-		}
-	}
-	tmpFile.Close()
-	defer os.Remove(tmpPath)
-
-	setProgress("압축을 해제하는 중...", -1)
-
-	// 임시 디렉토리에 먼저 추출 후 성공 시 이동 (실패 시 잔여 파일 방지)
-	tmpExtractDir, err := os.MkdirTemp("", "a301_extract_")
-	if err != nil {
-		return fmt.Errorf("임시 추출 디렉토리 생성 실패: %w", err)
-	}
-
-	if err := extractZip(tmpPath, tmpExtractDir); err != nil {
-		os.RemoveAll(tmpExtractDir)
-		return err
-	}
-
-	if err := moveContents(tmpExtractDir, destDir); err != nil {
-		os.RemoveAll(tmpExtractDir)
-		return fmt.Errorf("파일 이동 실패: %w", err)
-	}
-	os.RemoveAll(tmpExtractDir)
-	return nil
-}
-
-func extractZip(zipPath, destDir string) error {
-	r, err := zip.OpenReader(zipPath)
-	if err != nil {
-		return fmt.Errorf("zip 열기 실패: %w", err)
-	}
-	defer r.Close()
-
-	// 런처 자신의 파일명 (덮어쓰기 방지)
-	selfName := strings.ToLower(filepath.Base(os.Args[0]))
-
-	for _, f := range r.File {
-		// zip 내 최상위 디렉토리 제거 (A301/A301.exe → A301.exe)
-		clean := filepath.ToSlash(f.Name)
-		parts := strings.SplitN(clean, "/", 2)
-		var rel string
-		if len(parts) == 2 && parts[1] != "" {
-			rel = parts[1]
-		} else if len(parts) == 1 && !strings.Contains(clean, "/") && parts[0] != "" {
-			// 최상위에 직접 있는 파일 (디렉토리 없는 zip)
-			rel = parts[0]
-		} else {
-			// 최상위 디렉토리 자체("A301/") 등 → 스킵
-			continue
-		}
-
-		// 절대 경로 거부
-		if filepath.IsAbs(rel) {
-			return fmt.Errorf("잘못된 zip 경로 (절대 경로): %s", rel)
-		}
-		// NTFS ADS 방어: 경로에 ':' 포함 시 거부
-		if strings.Contains(rel, ":") {
-			return fmt.Errorf("잘못된 zip 경로 (ADS): %s", rel)
-		}
-
-		// 런처 파일 건너뜀
-		if strings.ToLower(filepath.Base(rel)) == selfName {
-			continue
-		}
-
-		dest := filepath.Join(destDir, filepath.FromSlash(rel))
-
-		// Zip Slip 방지: 추출 경로가 대상 디렉토리 안인지 검증
-		cleanDest := filepath.Clean(dest)
-		cleanBase := filepath.Clean(destDir) + string(os.PathSeparator)
-		if !strings.HasPrefix(cleanDest, cleanBase) && cleanDest != filepath.Clean(destDir) {
-			return fmt.Errorf("잘못된 zip 경로: %s", rel)
-		}
-
-		// Symlink 차단: zip 내 심볼릭 링크를 통한 경로 탈출 방지
-		if f.FileInfo().Mode()&os.ModeSymlink != 0 {
-			continue
-		}
-
-		if f.FileInfo().IsDir() {
-			os.MkdirAll(dest, 0755)
-			continue
-		}
-
-		if err := os.MkdirAll(filepath.Dir(dest), 0755); err != nil {
-			return err
-		}
-
-		rc, err := f.Open()
-		if err != nil {
-			return err
-		}
-		out, err := os.Create(dest)
-		if err != nil {
-			rc.Close()
-			return err
-		}
-		_, err = io.Copy(out, io.LimitReader(rc, maxExtractFileSize))
-		closeErr := out.Close()
-		rc.Close()
-		if err != nil {
-			return err
-		}
-		if closeErr != nil {
-			return fmt.Errorf("파일 닫기 실패: %w", closeErr)
-		}
-	}
-	return nil
-}
-
-func moveContents(srcDir, dstDir string) error {
-	entries, err := os.ReadDir(srcDir)
-	if err != nil {
-		return err
-	}
-	for _, e := range entries {
-		src := filepath.Join(srcDir, e.Name())
-		dst := filepath.Join(dstDir, e.Name())
-		if e.IsDir() {
-			if err := os.MkdirAll(dst, 0755); err != nil {
-				return err
-			}
-			if err := moveContents(src, dst); err != nil {
-				return err
-			}
-		} else {
-			os.Remove(dst) // 기존 파일 제거 (Rename 실패 방지)
-			if err := os.Rename(src, dst); err != nil {
-				// 드라이브가 다를 경우 복사 후 삭제
-				if err := copyFile(src, dst); err != nil {
-					os.Remove(dst) // 실패한 부분 파일 제거
-					return err
-				}
-				os.Remove(src) // 복사 성공 후 원본 삭제
-			}
-		}
-	}
-	return nil
-}
-
-func copyFile(src, dst string) error {
-	in, err := os.Open(src)
-	if err != nil {
-		return err
-	}
-	defer in.Close()
-	out, err := os.Create(dst)
-	if err != nil {
-		return err
-	}
-	if _, err = io.Copy(out, in); err != nil {
-		out.Close()
-		return err
-	}
-	return out.Close()
-}
-
-// ── Server info ──────────────────────────────────────────────────────────────
-
-// errNoRetry wraps errors that should not be retried (e.g. 4xx responses).
-type errNoRetry struct {
-	err error
-}
-
-func (e *errNoRetry) Error() string { return e.err.Error() }
-func (e *errNoRetry) Unwrap() error { return e.err }
-
-type downloadInfo struct {
-	FileHash     string `json:"fileHash"`
-	URL          string `json:"url"`
-	LauncherURL  string `json:"launcherUrl"`
-	LauncherHash string `json:"launcherHash"`
-}
-
-func fetchServerInfoOnce() (*downloadInfo, error) {
-	resp, err := apiClient.Get(serverInfoURL)
-	if err != nil {
-		return nil, fmt.Errorf("서버 연결 실패: %w", err)
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode == 404 {
-		return nil, &errNoRetry{fmt.Errorf("게임이 아직 준비되지 않았습니다")}
-	}
-	if resp.StatusCode >= 400 {
-		return nil, &errNoRetry{fmt.Errorf("서버 오류 (HTTP %d)", resp.StatusCode)}
-	}
-
-	var info downloadInfo
-	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&info); err != nil {
-		return nil, fmt.Errorf("서버 응답 파싱 실패: %w", err)
-	}
-	return &info, nil
-}
-
-func fetchServerInfo() (*downloadInfo, error) {
-	const maxRetries = 3
-	var lastErr error
-	for i := range maxRetries {
-		info, err := fetchServerInfoOnce()
-		if err == nil {
-			return info, nil
-		}
-		lastErr = err
-		// 4xx 에러는 재시도해도 의미 없음
-		var noRetry *errNoRetry
-		if errors.As(err, &noRetry) {
-			return nil, err
-		}
-		time.Sleep(time.Duration(1<<i) * time.Second) // 1s, 2s, 4s
-	}
-	return nil, fmt.Errorf("서버 연결 실패 (%d회 재시도): %w", maxRetries, lastErr)
-}
-
-// redeemTicket exchanges a one-time launch ticket for a fresh JWT access token.
-// The ticket has a 30-second TTL on the server and can only be used once.
-// 재시도 불필요 — ticket은 일회용이므로 한 번 사용(또는 만료)되면 소멸.
-func redeemTicket(ticket string) (string, error) {
-	return redeemTicketFrom(redeemTicketURL, ticket)
-}
-
-func redeemTicketFrom(url, ticket string) (string, error) {
-	client := &http.Client{Timeout: 10 * time.Second}
-	body := fmt.Sprintf(`{"ticket":"%s"}`, ticket)
-	resp, err := client.Post(url, "application/json", strings.NewReader(body))
-	if err != nil {
-		return "", fmt.Errorf("서버에 연결할 수 없습니다: %w", err)
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode != http.StatusOK {
-		return "", fmt.Errorf("런처 인증에 실패했습니다 (HTTP %d)", resp.StatusCode)
-	}
-
-	var result struct {
-		Token string `json:"token"`
-	}
-	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&result); err != nil {
-		return "", fmt.Errorf("서버 응답을 처리할 수 없습니다: %w", err)
-	}
-	if result.Token == "" {
-		return "", fmt.Errorf("서버가 토큰을 반환하지 않았습니다")
-	}
-	return result.Token, nil
-}
-
-func hashFile(path string) (string, error) {
-	f, err := os.Open(path)
-	if err != nil {
-		return "", err
-	}
-	defer f.Close()
-	h := sha256.New()
-	if _, err := io.Copy(h, f); err != nil {
-		return "", err
-	}
-	return hex.EncodeToString(h.Sum(nil)), nil
-}
-
-// ── Launcher path ────────────────────────────────────────────────────────────
-
-// installDir returns the fixed install directory: %LOCALAPPDATA%\A301
-func installDir() (string, error) {
-	localAppData := os.Getenv("LOCALAPPDATA")
-	if localAppData == "" {
-		return "", fmt.Errorf("LOCALAPPDATA 환경변수를 찾을 수 없습니다")
-	}
-	return filepath.Join(localAppData, "A301"), nil
-}
-
-// launcherPath returns the current executable's absolute path.
-func launcherPath() (string, error) {
-	exe, err := os.Executable()
-	if err != nil {
-		return "", err
-	}
-	return filepath.Abs(exe)
-}
-
-// ── Protocol install / uninstall ─────────────────────────────────────────────
-
-func install() error {
-	srcPath, err := launcherPath()
-	if err != nil {
-		return fmt.Errorf("실행 파일 경로를 찾을 수 없습니다: %w", err)
-	}
-
-	dir, err := installDir()
-	if err != nil {
-		return err
-	}
-	if err := os.MkdirAll(dir, 0755); err != nil {
-		return fmt.Errorf("설치 디렉토리 생성 실패: %w", err)
-	}
-
-	dstPath := filepath.Join(dir, "launcher.exe")
-
-	// 이미 설치 위치에서 실행 중이 아니면 복사
-	if !strings.EqualFold(srcPath, dstPath) {
-		if err := copyFile(srcPath, dstPath); err != nil {
-			return fmt.Errorf("런처 설치 실패: %w", err)
-		}
-	}
-
-	// 설치된 경로를 레지스트리에 등록
-	key, _, err := registry.CreateKey(registry.CURRENT_USER, `Software\Classes\`+protocolName, registry.SET_VALUE)
-	if err != nil {
-		return fmt.Errorf("레지스트리 키 생성 실패: %w", err)
-	}
-	defer key.Close()
-	if err := key.SetStringValue("", "URL:One of the plans Protocol"); err != nil {
-		return fmt.Errorf("프로토콜 값 설정 실패: %w", err)
-	}
-	if err := key.SetStringValue("URL Protocol", ""); err != nil {
-		return fmt.Errorf("URL Protocol 값 설정 실패: %w", err)
-	}
-
-	cmdKey, _, err := registry.CreateKey(registry.CURRENT_USER, `Software\Classes\`+protocolName+`\shell\open\command`, registry.SET_VALUE)
-	if err != nil {
-		return fmt.Errorf("command 키 생성 실패: %w", err)
-	}
-	defer cmdKey.Close()
-	return cmdKey.SetStringValue("", fmt.Sprintf(`"%s" "%%1"`, dstPath))
-}
-
-func uninstall() error {
-	paths := []string{
-		`Software\Classes\` + protocolName + `\shell\open\command`,
-		`Software\Classes\` + protocolName + `\shell\open`,
-		`Software\Classes\` + protocolName + `\shell`,
-		`Software\Classes\` + protocolName,
-	}
-	for _, p := range paths {
-		if err := registry.DeleteKey(registry.CURRENT_USER, p); err != nil && err != registry.ErrNotExist {
-			return err
-		}
-	}
-	return nil
-}
-
-// ── Game update check + download ─────────────────────────────────────────────
-
-func ensureGame(gameDir, gamePath string, serverInfo *downloadInfo) error {
-	if serverInfo.FileHash == "" {
-		return fmt.Errorf("서버에서 유효한 파일 정보를 받지 못했습니다")
-	}
-
-	needsDownload := false
-
-	if _, err := os.Stat(gamePath); os.IsNotExist(err) {
-		needsDownload = true
-	} else if err != nil {
-		return fmt.Errorf("게임 파일 확인 실패: %w", err)
-	} else {
-		localHash, err := hashFile(gamePath)
-		if err != nil {
-			return fmt.Errorf("파일 검증 실패: %w", err)
-		}
-		if !strings.EqualFold(localHash, serverInfo.FileHash) {
-			needsDownload = true
-		}
-	}
-
-	if needsDownload {
-		if serverInfo.URL == "" {
-			return fmt.Errorf("다운로드 URL이 없습니다")
-		}
-		u, err := url.Parse(serverInfo.URL)
-		if err != nil || (u.Scheme != "https" && u.Scheme != "http") {
-			return fmt.Errorf("유효하지 않은 다운로드 URL")
-		}
-		if err := downloadWithProgress(serverInfo.URL, gameDir); err != nil {
-			return fmt.Errorf("게임 설치 실패: %w", err)
-		}
-		if serverInfo.FileHash != "" {
-			newHash, err := hashFile(gamePath)
-			if err != nil {
-				return fmt.Errorf("다운로드 후 파일 검증 실패: %w", err)
-			}
-			if !strings.EqualFold(newHash, serverInfo.FileHash) {
-				os.Remove(gamePath)
-				return fmt.Errorf("다운로드된 파일의 해시가 일치하지 않습니다 (파일이 손상되었을 수 있습니다)")
-			}
-		}
-	}
-
-	return nil
-}
-
-// ── Launcher self-update ─────────────────────────────────────────────────────
-
-// downloadFile downloads a file from url to destPath using apiClient.
-func downloadFile(dlURL, destPath string) error {
-	resp, err := apiClient.Get(dlURL)
-	if err != nil {
-		return err
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode != http.StatusOK {
-		return fmt.Errorf("HTTP %d", resp.StatusCode)
-	}
-	f, err := os.Create(destPath)
-	if err != nil {
-		return err
-	}
-	_, err = io.Copy(f, io.LimitReader(resp.Body, maxDownloadSize))
-	if closeErr := f.Close(); closeErr != nil && err == nil {
-		err = closeErr
-	}
-	return err
-}
-
-// ensureLauncher checks if the installed launcher is up-to-date and replaces it if not.
-// Since a running exe cannot overwrite itself on Windows, we:
-// 1. Download the new launcher to a .new temp file
-// 2. Rename the current exe to .old
-// 3. Rename .new to the current exe path
-// 4. Return updated=true so the caller can re-exec
-func ensureLauncher(serverInfo *downloadInfo) (updated bool, err error) {
-	if serverInfo.LauncherHash == "" {
-		return false, nil // server doesn't provide launcher hash, skip
-	}
-
-	installedPath, err := launcherPath()
-	if err != nil {
-		return false, nil // can't determine own path, skip
-	}
-
-	localHash, err := hashFile(installedPath)
-	if err != nil {
-		return false, nil
-	}
-
-	if strings.EqualFold(localHash, serverInfo.LauncherHash) {
-		return false, nil // already up-to-date
-	}
-
-	// Determine download URL
-	dlURL := serverInfo.LauncherURL
-	if dlURL == "" {
-		return false, nil // no launcher URL available
-	}
-
-	// Download new launcher to temp file
-	newPath := installedPath + ".new"
-	if err := downloadFile(dlURL, newPath); err != nil {
-		os.Remove(newPath)
-		return false, fmt.Errorf("런처 업데이트 다운로드 실패: %w", err)
-	}
-
-	// Verify downloaded file hash
-	newHash, err := hashFile(newPath)
-	if err != nil {
-		os.Remove(newPath)
-		return false, fmt.Errorf("런처 검증 실패: %w", err)
-	}
-	if !strings.EqualFold(newHash, serverInfo.LauncherHash) {
-		os.Remove(newPath)
-		return false, fmt.Errorf("런처 해시 불일치")
-	}
-
-	// Replace: current → .old, new → current
-	oldPath := installedPath + ".old"
-	os.Remove(oldPath) // remove previous .old if exists
-	if err := os.Rename(installedPath, oldPath); err != nil {
-		os.Remove(newPath)
-		return false, fmt.Errorf("런처 교체 실패: %w", err)
-	}
-	if err := os.Rename(newPath, installedPath); err != nil {
-		// Try to restore
-		if restoreErr := os.Rename(oldPath, installedPath); restoreErr != nil {
-			return false, fmt.Errorf("런처 교체 실패 및 복원 불가: %w (원인: %v)", restoreErr, err)
-		}
-		return false, fmt.Errorf("런처 교체 실패: %w", err)
-	}
-
-	return true, nil
-}
-
-// ── Cleanup helpers ──────────────────────────────────────────────────────────
-
-// cleanupOldFiles removes .old and .new leftover files from previous launcher updates.
-func cleanupOldFiles(dir string) {
-	entries, err := os.ReadDir(dir)
-	if err != nil {
-		return
-	}
-	for _, e := range entries {
-		name := e.Name()
-		if strings.HasSuffix(name, ".old") || strings.HasSuffix(name, ".new") {
-			os.Remove(filepath.Join(dir, name))
-		}
-	}
-}
-
-// ── URI handler ──────────────────────────────────────────────────────────────
-
 func handleURI(rawURI string) error {
 	parsed, err := url.Parse(rawURI)
 	if err != nil {
@@ -1145,7 +75,6 @@ func handleURI(rawURI string) error {
 	if updated, updateErr := ensureLauncher(serverInfo); updateErr != nil {
 		_ = updateErr // 업데이트 실패는 치명적이지 않음
 	} else if updated {
-		// 새 런처로 재실행
 		cmd := exec.Command(os.Args[0], os.Args[1:]...)
 		if err := cmd.Start(); err != nil {
 			return fmt.Errorf("새 런처 시작 실패: %w", err)
@@ -1166,29 +95,8 @@ func handleURI(rawURI string) error {
 	return nil
 }
 
-// ── Entry point ──────────────────────────────────────────────────────────────
-
-func activateExistingWindow() {
-	className, _ := windows.UTF16PtrFromString("A301Progress")
-	hwnd, _, _ := findWindowWProc.Call(uintptr(unsafe.Pointer(className)), 0)
-	if hwnd != 0 {
-		setForegroundWindowProc.Call(hwnd)
-	}
-}
-
-func acquireSingleInstance() bool {
-	name, _ := windows.UTF16PtrFromString("Global\\A301LauncherMutex")
-	_, _, err := createMutexWProc.Call(0, 0, uintptr(unsafe.Pointer(name)))
-	// ERROR_ALREADY_EXISTS = 183
-	if errno, ok := err.(syscall.Errno); ok && errno == 183 {
-		return false
-	}
-	return true
-}
-
 func main() {
 	// DLL Hijacking 방어: 시스템 디렉토리에서만 DLL 로드
-	// SetDefaultDllDirectories는 Windows 8+ (KB2533623)에서 사용 가능
 	const loadLibrarySearchSystem32 = 0x00000800
 	kernel32.NewProc("SetDefaultDllDirectories").Call(loadLibrarySearchSystem32)
 
diff --git a/protocol.go b/protocol.go
new file mode 100644
index 0000000..ae840d8
--- /dev/null
+++ b/protocol.go
@@ -0,0 +1,181 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+const (
+	protocolName    = "a301"
+	gameExeName     = "A301.exe"
+	serverInfoURL   = "https://a301.api.tolelom.xyz/api/download/info"
+	redeemTicketURL = "https://a301.api.tolelom.xyz/api/auth/redeem-ticket"
+)
+
+// errNoRetry wraps errors that should not be retried (e.g. 4xx responses).
+type errNoRetry struct {
+	err error
+}
+
+func (e *errNoRetry) Error() string { return e.err.Error() }
+func (e *errNoRetry) Unwrap() error { return e.err }
+
+type downloadInfo struct {
+	FileHash     string `json:"fileHash"`
+	URL          string `json:"url"`
+	LauncherURL  string `json:"launcherUrl"`
+	LauncherHash string `json:"launcherHash"`
+}
+
+// installDir returns the fixed install directory: %LOCALAPPDATA%\A301
+func installDir() (string, error) {
+	localAppData := os.Getenv("LOCALAPPDATA")
+	if localAppData == "" {
+		return "", fmt.Errorf("LOCALAPPDATA 환경변수를 찾을 수 없습니다")
+	}
+	return filepath.Join(localAppData, "A301"), nil
+}
+
+// launcherPath returns the current executable's absolute path.
+func launcherPath() (string, error) {
+	exe, err := os.Executable()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Abs(exe)
+}
+
+func install() error {
+	srcPath, err := launcherPath()
+	if err != nil {
+		return fmt.Errorf("실행 파일 경로를 찾을 수 없습니다: %w", err)
+	}
+
+	dir, err := installDir()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return fmt.Errorf("설치 디렉토리 생성 실패: %w", err)
+	}
+
+	dstPath := filepath.Join(dir, "launcher.exe")
+
+	if !strings.EqualFold(srcPath, dstPath) {
+		if err := copyFile(srcPath, dstPath); err != nil {
+			return fmt.Errorf("런처 설치 실패: %w", err)
+		}
+	}
+
+	key, _, err := registry.CreateKey(registry.CURRENT_USER, `Software\Classes\`+protocolName, registry.SET_VALUE)
+	if err != nil {
+		return fmt.Errorf("레지스트리 키 생성 실패: %w", err)
+	}
+	defer key.Close()
+	if err := key.SetStringValue("", "URL:One of the plans Protocol"); err != nil {
+		return fmt.Errorf("프로토콜 값 설정 실패: %w", err)
+	}
+	if err := key.SetStringValue("URL Protocol", ""); err != nil {
+		return fmt.Errorf("URL Protocol 값 설정 실패: %w", err)
+	}
+
+	cmdKey, _, err := registry.CreateKey(registry.CURRENT_USER, `Software\Classes\`+protocolName+`\shell\open\command`, registry.SET_VALUE)
+	if err != nil {
+		return fmt.Errorf("command 키 생성 실패: %w", err)
+	}
+	defer cmdKey.Close()
+	return cmdKey.SetStringValue("", fmt.Sprintf(`"%s" "%%1"`, dstPath))
+}
+
+func uninstall() error {
+	paths := []string{
+		`Software\Classes\` + protocolName + `\shell\open\command`,
+		`Software\Classes\` + protocolName + `\shell\open`,
+		`Software\Classes\` + protocolName + `\shell`,
+		`Software\Classes\` + protocolName,
+	}
+	for _, p := range paths {
+		if err := registry.DeleteKey(registry.CURRENT_USER, p); err != nil && err != registry.ErrNotExist {
+			return err
+		}
+	}
+	return nil
+}
+
+func fetchServerInfoOnce() (*downloadInfo, error) {
+	resp, err := apiClient.Get(serverInfoURL)
+	if err != nil {
+		return nil, fmt.Errorf("서버 연결 실패: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == 404 {
+		return nil, &errNoRetry{fmt.Errorf("게임이 아직 준비되지 않았습니다")}
+	}
+	if resp.StatusCode >= 400 {
+		return nil, &errNoRetry{fmt.Errorf("서버 오류 (HTTP %d)", resp.StatusCode)}
+	}
+
+	var info downloadInfo
+	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&info); err != nil {
+		return nil, fmt.Errorf("서버 응답 파싱 실패: %w", err)
+	}
+	return &info, nil
+}
+
+func fetchServerInfo() (*downloadInfo, error) {
+	const maxRetries = 3
+	var lastErr error
+	for i := range maxRetries {
+		info, err := fetchServerInfoOnce()
+		if err == nil {
+			return info, nil
+		}
+		lastErr = err
+		var noRetry *errNoRetry
+		if errors.As(err, &noRetry) {
+			return nil, err
+		}
+		time.Sleep(time.Duration(1<<i) * time.Second)
+	}
+	return nil, fmt.Errorf("서버 연결 실패 (%d회 재시도): %w", maxRetries, lastErr)
+}
+
+// redeemTicket exchanges a one-time launch ticket for a fresh JWT access token.
+func redeemTicket(ticket string) (string, error) {
+	return redeemTicketFrom(redeemTicketURL, ticket)
+}
+
+func redeemTicketFrom(url, ticket string) (string, error) {
+	client := &http.Client{Timeout: 10 * time.Second}
+	body := fmt.Sprintf(`{"ticket":"%s"}`, ticket)
+	resp, err := client.Post(url, "application/json", strings.NewReader(body))
+	if err != nil {
+		return "", fmt.Errorf("서버에 연결할 수 없습니다: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("런처 인증에 실패했습니다 (HTTP %d)", resp.StatusCode)
+	}
+
+	var result struct {
+		Token string `json:"token"`
+	}
+	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&result); err != nil {
+		return "", fmt.Errorf("서버 응답을 처리할 수 없습니다: %w", err)
+	}
+	if result.Token == "" {
+		return "", fmt.Errorf("서버가 토큰을 반환하지 않았습니다")
+	}
+	return result.Token, nil
+}
diff --git a/ui.go b/ui.go
new file mode 100644
index 0000000..e9c4d6b
--- /dev/null
+++ b/ui.go
@@ -0,0 +1,387 @@
+package main
+
+import (
+	"fmt"
+	"runtime"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+// Win32 constants
+const (
+	wmDestroy        uint32 = 0x0002
+	wmClose          uint32 = 0x0010
+	wmSetFont        uint32 = 0x0030
+	wmSetText        uint32 = 0x000C
+	wmCtlColorStatic uint32 = 0x0138
+	wmAppDone        uint32 = 0x8001
+
+	wsPopup   uintptr = 0x80000000
+	wsCaption uintptr = 0x00C00000
+	wsSysMenu uintptr = 0x00080000
+	wsChild   uintptr = 0x40000000
+	wsVisible uintptr = 0x10000000
+	ssCenter  uintptr = 0x00000001
+
+	pbsSmooth      uintptr = 0x01
+	pbmSetRange32  uint32  = 0x0406
+	pbmSetPos      uint32  = 0x0402
+	pbmSetBarColor uint32  = 0x0409
+	pbmSetBkColor  uint32  = 0x2001
+
+	setBkModeTransparent = 1
+
+	swShow     = 5
+	smCxScreen = 0
+	smCyScreen = 1
+
+	mbOK    uintptr = 0x00000000
+	mbInfo  uintptr = 0x00000040
+	mbError uintptr = 0x00000010
+	mbYesNo uintptr = 0x00000004
+	mbQ     uintptr = 0x00000020
+	idYes           = 6
+
+	iccProgressClass uint32 = 0x00000020
+)
+
+// rgb builds a COLORREF from R, G, B components.
+func rgb(r, g, b uint8) uintptr {
+	return uintptr(r) | (uintptr(g) << 8) | (uintptr(b) << 16)
+}
+
+// 웹사이트 색상과 동일한 팔레트
+var (
+	colorBg         = rgb(46, 44, 47)   // #2E2C2F
+	colorText       = rgb(200, 200, 200) // 밝은 회색
+	colorAccent     = rgb(186, 205, 176) // #BACDB0
+	colorProgressBg = rgb(65, 63, 67)   // bg보다 약간 밝은 색
+)
+
+var (
+	user32   = windows.NewLazySystemDLL("user32.dll")
+	kernel32 = windows.NewLazySystemDLL("kernel32.dll")
+	gdi32    = windows.NewLazySystemDLL("gdi32.dll")
+	comctl32 = windows.NewLazySystemDLL("comctl32.dll")
+	uxtheme  = windows.NewLazySystemDLL("uxtheme.dll")
+
+	messageBoxWProc                   = user32.NewProc("MessageBoxW")
+	registerClassExWProc              = user32.NewProc("RegisterClassExW")
+	createWindowExWProc               = user32.NewProc("CreateWindowExW")
+	showWindowProc                    = user32.NewProc("ShowWindow")
+	updateWindowProc                  = user32.NewProc("UpdateWindow")
+	getMessageWProc                   = user32.NewProc("GetMessageW")
+	translateMsgProc                  = user32.NewProc("TranslateMessage")
+	dispatchMsgWProc                  = user32.NewProc("DispatchMessageW")
+	sendMessageWProc                  = user32.NewProc("SendMessageW")
+	postMessageWProc                  = user32.NewProc("PostMessageW")
+	defWindowProcWProc                = user32.NewProc("DefWindowProcW")
+	destroyWindowProc                 = user32.NewProc("DestroyWindow")
+	postQuitMsgProc                   = user32.NewProc("PostQuitMessage")
+	getSystemMetricsProc              = user32.NewProc("GetSystemMetrics")
+	getDpiForSystemProc               = user32.NewProc("GetDpiForSystem")
+	setProcessDpiAwarenessContextProc = user32.NewProc("SetProcessDpiAwarenessContext")
+	findWindowWProc                   = user32.NewProc("FindWindowW")
+	setForegroundWindowProc           = user32.NewProc("SetForegroundWindow")
+	createMutexWProc                  = kernel32.NewProc("CreateMutexW")
+	getModuleHandleWProc              = kernel32.NewProc("GetModuleHandleW")
+	createFontIndirectWProc           = gdi32.NewProc("CreateFontIndirectW")
+	createSolidBrushProc              = gdi32.NewProc("CreateSolidBrush")
+	setTextColorProc                  = gdi32.NewProc("SetTextColor")
+	setBkModeProc                     = gdi32.NewProc("SetBkMode")
+	deleteObjectProc                  = gdi32.NewProc("DeleteObject")
+	initCommonControlsExProc          = comctl32.NewProc("InitCommonControlsEx")
+	setWindowThemeProc                = uxtheme.NewProc("SetWindowTheme")
+
+	wndProcCb         uintptr
+	titleLabelHwnd    uintptr
+	progressLabelHwnd uintptr
+	progressBarHwnd   uintptr
+	hBrushBg          uintptr
+)
+
+type wndClassExW struct {
+	cbSize        uint32
+	style         uint32
+	lpfnWndProc   uintptr
+	cbClsExtra    int32
+	cbWndExtra    int32
+	hInstance     uintptr
+	hIcon         uintptr
+	hCursor       uintptr
+	hbrBackground uintptr
+	lpszMenuName  *uint16
+	lpszClassName *uint16
+	hIconSm       uintptr
+}
+
+type msgW struct {
+	hwnd    uintptr
+	message uint32
+	wParam  uintptr
+	lParam  uintptr
+	time    uint32
+	ptX     int32
+	ptY     int32
+}
+
+type initCommonControlsExS struct {
+	dwSize uint32
+	dwICC  uint32
+}
+
+type logFontW struct {
+	lfHeight         int32
+	lfWidth          int32
+	lfEscapement     int32
+	lfOrientation    int32
+	lfWeight         int32
+	lfItalic         byte
+	lfUnderline      byte
+	lfStrikeOut      byte
+	lfCharSet        byte
+	lfOutPrecision   byte
+	lfClipPrecision  byte
+	lfQuality        byte
+	lfPitchAndFamily byte
+	lfFaceName       [32]uint16
+}
+
+func init() {
+	wndProcCb = syscall.NewCallback(progressWndProc)
+}
+
+func enableDPIAwareness() {
+	// DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 = -4 (Windows 10 1703+)
+	setProcessDpiAwarenessContextProc.Call(^uintptr(3))
+}
+
+func getSystemDPI() uint32 {
+	dpi, _, _ := getDpiForSystemProc.Call()
+	if dpi == 0 {
+		return 96
+	}
+	return uint32(dpi)
+}
+
+// dpiScale scales a base-96-DPI pixel value to the system DPI.
+func dpiScale(px int, dpi uint32) uintptr {
+	return uintptr(int(float64(px)*float64(dpi)/96.0 + 0.5))
+}
+
+func createUIFont(pointSize int, dpi uint32, bold bool) uintptr {
+	weight := int32(400) // FW_NORMAL
+	if bold {
+		weight = 700 // FW_BOLD
+	}
+	lf := logFontW{
+		lfHeight:  -int32(pointSize) * int32(dpi) / 72,
+		lfWeight:  weight,
+		lfCharSet: 1, // DEFAULT_CHARSET
+		lfQuality: 5, // CLEARTYPE_QUALITY
+	}
+	face, _ := windows.UTF16FromString("Segoe UI")
+	copy(lf.lfFaceName[:], face)
+	font, _, _ := createFontIndirectWProc.Call(uintptr(unsafe.Pointer(&lf)))
+	// font가 0이면 시스템 기본 폰트가 사용됨 (WM_SETFONT에 0 전달 시 기본값)
+	return font
+}
+
+func initCommonControls() {
+	icc := initCommonControlsExS{
+		dwSize: uint32(unsafe.Sizeof(initCommonControlsExS{})),
+		dwICC:  iccProgressClass,
+	}
+	initCommonControlsExProc.Call(uintptr(unsafe.Pointer(&icc)))
+}
+
+func msgBox(title, text string, flags uintptr) int {
+	t, err := windows.UTF16PtrFromString(title)
+	if err != nil {
+		return 0
+	}
+	m, err := windows.UTF16PtrFromString(text)
+	if err != nil {
+		return 0
+	}
+	ret, _, _ := messageBoxWProc.Call(0, uintptr(unsafe.Pointer(m)), uintptr(unsafe.Pointer(t)), flags)
+	return int(ret)
+}
+
+func progressWndProc(hwnd, uMsg, wParam, lParam uintptr) uintptr {
+	switch uint32(uMsg) {
+	case wmClose:
+		ret := msgBox("One of the plans 런처", "다운로드를 취소하시겠습니까?", mbYesNo|mbQ)
+		if ret == idYes {
+			downloadCancelled.Store(true)
+			destroyWindowProc.Call(hwnd)
+		}
+		return 0
+	case wmDestroy:
+		postQuitMsgProc.Call(0)
+		return 0
+	case wmAppDone:
+		destroyWindowProc.Call(hwnd)
+		return 0
+	case wmCtlColorStatic:
+		hdc := wParam
+		setBkModeProc.Call(hdc, setBkModeTransparent)
+		if lParam == titleLabelHwnd {
+			setTextColorProc.Call(hdc, colorAccent)
+		} else {
+			setTextColorProc.Call(hdc, colorText)
+		}
+		return hBrushBg
+	}
+	ret, _, _ := defWindowProcWProc.Call(hwnd, uMsg, wParam, lParam)
+	return ret
+}
+
+func setProgress(text string, pct int) {
+	if text != "" {
+		t, err := windows.UTF16PtrFromString(text)
+		if err == nil {
+			sendMessageWProc.Call(progressLabelHwnd, uintptr(wmSetText), 0, uintptr(unsafe.Pointer(t)))
+		}
+	}
+	if pct >= 0 {
+		sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetPos), uintptr(pct), 0)
+	}
+}
+
+// downloadWithProgress shows a DPI-aware dark-themed progress window and downloads+extracts the zip.
+// Must be called from the main goroutine (Win32 message loop requirement).
+func downloadWithProgress(downloadURL, destDir string) error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	initCommonControls()
+	dpi := getSystemDPI()
+	s := func(px int) uintptr { return dpiScale(px, dpi) }
+
+	hBrushBg, _, _ = createSolidBrushProc.Call(colorBg)
+	defer deleteObjectProc.Call(hBrushBg)
+
+	hInstance, _, _ := getModuleHandleWProc.Call(0)
+
+	className, _ := windows.UTF16PtrFromString("A301Progress")
+	wc := wndClassExW{
+		cbSize:        uint32(unsafe.Sizeof(wndClassExW{})),
+		lpfnWndProc:   wndProcCb,
+		hInstance:     hInstance,
+		lpszClassName: className,
+		hbrBackground: hBrushBg,
+	}
+	atom, _, _ := registerClassExWProc.Call(uintptr(unsafe.Pointer(&wc)))
+	if atom == 0 {
+		return fmt.Errorf("윈도우 클래스 등록 실패")
+	}
+
+	screenW, _, _ := getSystemMetricsProc.Call(smCxScreen)
+	screenH, _, _ := getSystemMetricsProc.Call(smCyScreen)
+	winW := s(440)
+	winH := s(152)
+	x := (screenW - winW) / 2
+	y := (screenH - winH) / 2
+
+	titleStr, _ := windows.UTF16PtrFromString("One of the plans 런처")
+	hwnd, _, _ := createWindowExWProc.Call(
+		0,
+		uintptr(unsafe.Pointer(className)),
+		uintptr(unsafe.Pointer(titleStr)),
+		wsPopup|wsCaption|wsSysMenu|wsVisible,
+		x, y, winW, winH,
+		0, 0, hInstance, 0,
+	)
+	if hwnd == 0 {
+		return fmt.Errorf("다운로드 창 생성 실패")
+	}
+
+	titleFont := createUIFont(13, dpi, true)
+	defer deleteObjectProc.Call(titleFont)
+	statusFont := createUIFont(9, dpi, false)
+	defer deleteObjectProc.Call(statusFont)
+
+	staticClass, _ := windows.UTF16PtrFromString("STATIC")
+
+	titleText, _ := windows.UTF16PtrFromString("One of the plans")
+	titleLabelHwnd, _, _ = createWindowExWProc.Call(
+		0,
+		uintptr(unsafe.Pointer(staticClass)),
+		uintptr(unsafe.Pointer(titleText)),
+		wsChild|wsVisible|ssCenter,
+		s(20), s(14), winW-s(40), s(28),
+		hwnd, 0, hInstance, 0,
+	)
+	sendMessageWProc.Call(titleLabelHwnd, uintptr(wmSetFont), titleFont, 1)
+
+	initText, _ := windows.UTF16PtrFromString("게임 파일을 다운로드하는 중...")
+	progressLabelHwnd, _, _ = createWindowExWProc.Call(
+		0,
+		uintptr(unsafe.Pointer(staticClass)),
+		uintptr(unsafe.Pointer(initText)),
+		wsChild|wsVisible|ssCenter,
+		s(20), s(52), winW-s(40), s(20),
+		hwnd, 0, hInstance, 0,
+	)
+	sendMessageWProc.Call(progressLabelHwnd, uintptr(wmSetFont), statusFont, 1)
+
+	progressClass, _ := windows.UTF16PtrFromString("msctls_progress32")
+	progressBarHwnd, _, _ = createWindowExWProc.Call(
+		0,
+		uintptr(unsafe.Pointer(progressClass)),
+		0,
+		wsChild|wsVisible|pbsSmooth,
+		s(20), s(82), winW-s(40), s(18),
+		hwnd, 0, hInstance, 0,
+	)
+	sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetRange32), 0, 100)
+
+	empty, _ := windows.UTF16PtrFromString("")
+	setWindowThemeProc.Call(progressBarHwnd, uintptr(unsafe.Pointer(empty)), uintptr(unsafe.Pointer(empty)))
+	sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetBarColor), 0, colorAccent)
+	sendMessageWProc.Call(progressBarHwnd, uintptr(pbmSetBkColor), 0, colorProgressBg)
+
+	showWindowProc.Call(hwnd, swShow)
+	updateWindowProc.Call(hwnd)
+
+	downloadCancelled.Store(false)
+
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- doDownload(downloadURL, destDir)
+		postMessageWProc.Call(hwnd, uintptr(wmAppDone), 0, 0)
+	}()
+
+	var m msgW
+	for {
+		ret, _, _ := getMessageWProc.Call(uintptr(unsafe.Pointer(&m)), 0, 0, 0)
+		if ret == 0 || ret == ^uintptr(0) {
+			break
+		}
+		translateMsgProc.Call(uintptr(unsafe.Pointer(&m)))
+		dispatchMsgWProc.Call(uintptr(unsafe.Pointer(&m)))
+	}
+
+	return <-errCh
+}
+
+func activateExistingWindow() {
+	className, _ := windows.UTF16PtrFromString("A301Progress")
+	hwnd, _, _ := findWindowWProc.Call(uintptr(unsafe.Pointer(className)), 0)
+	if hwnd != 0 {
+		setForegroundWindowProc.Call(hwnd)
+	}
+}
+
+func acquireSingleInstance() bool {
+	name, _ := windows.UTF16PtrFromString("Global\\A301LauncherMutex")
+	_, _, err := createMutexWProc.Call(0, 0, uintptr(unsafe.Pointer(name)))
+	// ERROR_ALREADY_EXISTS = 183
+	if errno, ok := err.(syscall.Errno); ok && errno == 183 {
+		return false
+	}
+	return true
+}