Wire yt-dlp.exe prep into resource pack installer

Add src/installer-rp/ytdlp.ts that downloads
https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp.exe
into %appdata%/.mc_custom/yt-dlp.exe (fixed path, Windows-only since
the installer is shipped as .exe). If the file is already there and
--version works it is reused; otherwise it is re-downloaded and
verified. The server's existing OS-aware ensureYtDlp stays intact.

The install IPC handler now calls ensureYtDlpExe() in step 2-1 and
logs the resolved path. Music / image / zip / place steps are still
stubbed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/installer-rp/main.ts

@@ -8,6 +8,7 @@ import { URL } from 'node:url'
 import type { Manifest, PackList } from '../shared/types.js'
 import { getAppDataDir, getMcCustomDir } from '../shared/paths.js'
 import type { RpFetchedPack } from './types.js'
+import { ensureYtDlpExe } from './ytdlp.js'
 
 interface RpInstallerState {
   manifestUrl: string
@@ -141,9 +142,10 @@ ipcMain.handle('rp:install:start', async (): Promise<{ resourcepackPath: string
   await fsp.mkdir(tempRoot, { recursive: true })
 
   try {
-    // 2-1. yt-dlp 준비
+    // 2-1. yt-dlp 준비 (%appdata%/.mc_custom/yt-dlp.exe)
-    sendLog('yt-dlp 준비 중… (TODO)')
+    sendLog('yt-dlp 준비 중…')
-    // TODO: ensureYtDlp() — shared 모듈로 분리 예정.
+    const ytDlpBin = await ensureYtDlpExe(sendLog)
+    sendLog(`yt-dlp 경로: ${ytDlpBin}`)
     throwIfCancelled()
 
     // 2-2. 음악 다운로드 (1번부터 순차, ogg 변환)

src/installer-rp/ytdlp.ts

@@ -0,0 +1,109 @@
+import { spawn } from 'node:child_process'
+import { promises as fs, createWriteStream, constants as fsConst } from 'node:fs'
+import path from 'node:path'
+import https from 'node:https'
+import http from 'node:http'
+import { getMcCustomDir } from '../shared/paths.js'
+
+/**
+ * 리소스팩 간편설치기는 Windows .exe 로 배포되므로 yt-dlp.exe 한 종류만 사용.
+ * 경로: %appdata%/.mc_custom/yt-dlp.exe
+ */
+export function getYtDlpExePath(): string {
+  return path.join(getMcCustomDir(), 'yt-dlp.exe')
+}
+
+const YT_DLP_DOWNLOAD_URL =
+  'https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp.exe'
+
+let installPromise: Promise<string> | null = null
+
+/**
+ * %appdata%/.mc_custom/yt-dlp.exe 가 없거나 실행 불가능하면 GitHub Releases
+ * 의 최신 yt-dlp.exe 를 받아 설치하고, 그 절대경로를 돌려준다.
+ */
+export async function ensureYtDlpExe(
+  log?: (line: string) => void
+): Promise<string> {
+  const target = getYtDlpExePath()
+  if (await canExecute(target)) {
+    log?.(`yt-dlp.exe 이미 있음: ${target}`)
+    return target
+  }
+  if (installPromise) return installPromise
+
+  installPromise = (async () => {
+    try {
+      await fs.mkdir(path.dirname(target), { recursive: true })
+      log?.(`yt-dlp.exe 다운로드 중: ${YT_DLP_DOWNLOAD_URL}`)
+      await downloadToFile(YT_DLP_DOWNLOAD_URL, target)
+      const okVersion = await probeVersion(target)
+      if (!okVersion) {
+        throw new Error('yt-dlp.exe 다운로드는 됐지만 실행 검증에 실패했습니다.')
+      }
+      log?.(`yt-dlp.exe 준비 완료: ${target}`)
+      return target
+    } catch (err) {
+      // 부분 다운로드 흔적 정리
+      try { await fs.unlink(target) } catch { /* noop */ }
+      throw new Error(
+        'yt-dlp.exe 자동 설치 실패: ' +
+          (err instanceof Error ? err.message : String(err))
+      )
+    } finally {
+      installPromise = null
+    }
+  })()
+  return installPromise
+}
+
+async function canExecute(filePath: string): Promise<boolean> {
+  try {
+    await fs.access(filePath, fsConst.F_OK)
+  } catch {
+    return false
+  }
+  return probeVersion(filePath)
+}
+
+function probeVersion(bin: string): Promise<boolean> {
+  return new Promise((resolve) => {
+    const child = spawn(bin, ['--version'], { stdio: ['ignore', 'pipe', 'pipe'] })
+    let ok = false
+    child.stdout.on('data', () => { ok = true })
+    child.on('error', () => resolve(false))
+    child.on('close', (code) => resolve(ok && code === 0))
+  })
+}
+
+/** GitHub Releases 의 latest URL 은 302 리다이렉트를 사용하므로 따라가며 받음. */
+function downloadToFile(url: string, dest: string, redirects = 0): Promise<void> {
+  return new Promise((resolve, reject) => {
+    if (redirects > 8) {
+      reject(new Error('redirect 가 너무 많습니다.'))
+      return
+    }
+    const lib = url.startsWith('https://') ? https : http
+    const req = lib.get(url, {
+      headers: { 'user-agent': 'mc-music-quiz-rp-installer' }
+    }, (res) => {
+      const code = res.statusCode || 0
+      if (code >= 300 && code < 400 && res.headers.location) {
+        res.resume()
+        downloadToFile(res.headers.location, dest, redirects + 1).then(resolve, reject)
+        return
+      }
+      if (code !== 200) {
+        res.resume()
+        reject(new Error(`HTTP ${code} (${url})`))
+        return
+      }
+      const out = createWriteStream(dest)
+      res.pipe(out)
+      out.on('finish', () => out.close((err) => err ? reject(err) : resolve()))
+      out.on('error', reject)
+      res.on('error', reject)
+    })
+    req.on('error', reject)
+  })
+}