refactor(main): execFileAsync helper — unify the 5 spawn-and-read sites

Replace the hand-rolled `new Promise((resolve) => execFile(…, cb))` wrappers in
probe / ytdlp (×2) / ffmpeg / indexer.probeFlat / download.probeMeta with one
lib/exec.ts execFileAsync returning a normalized
{ok,stdout,stderr,timedOut,error} that never rejects. Each caller keeps its own
error mapping (timedOut -> "Timed out …" vs stderr) and JSON parsing; behaviour
is unchanged. windowsHide defaults on; per-call timeout/maxBuffer preserved.

Foundation for CC4/CC5 — the stdout line-buffer half lands with SIMP5, the
net.request half with SIMP16, at which point those checkboxes close.

Unit-tested (exec.test.ts) against the node binary: ok / stderr+nonzero-exit /
missing-binary / timeout. typecheck + 262 tests + eslint + prettier green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/probe.ts

@@ -1,6 +1,6 @@
-import { execFile } from 'child_process'
 import { existsSync } from 'fs'
 import { getYtdlpPath, YTDLP_MISSING_MSG } from './binaries'
+import { execFileAsync } from './lib/exec'
 import { PROBE_MAX_BUFFER, PROBE_TIMEOUT_MS } from './constants'
 import { fmtBytes } from '@shared/format'
 import { cleanError } from './log'
@@ -114,52 +114,40 @@ function buildPlaylist(data: RawInfo): PlaylistInfo {
  * its format list) or, when the URL is a playlist, the flat list of its entries.
  * `--flat-playlist` is a no-op for a lone video, so one call covers both cases.
  */
-export function probeMedia(url: string): Promise<ProbeResult> {
+export async function probeMedia(url: string): Promise<ProbeResult> {
   const ytdlp = getYtdlpPath()
   if (!existsSync(ytdlp)) {
-    return Promise.resolve({
-      ok: false,
-      error: YTDLP_MISSING_MSG
-    })
+    return { ok: false, error: YTDLP_MISSING_MSG }
   }
   let target: string
   try {
     target = assertHttpUrl(url) // normalised form (audit F5)
   } catch (e) {
-    return Promise.resolve({ ok: false, error: (e as Error).message })
+    return { ok: false, error: (e as Error).message }
   }
 
-  return new Promise((resolve) => {
-    execFile(
-      ytdlp,
-      // `--` terminates option parsing so the URL can never be read as a flag.
-      ['-J', '--flat-playlist', '--no-warnings', '--', target],
-      { windowsHide: true, maxBuffer: PROBE_MAX_BUFFER, timeout: PROBE_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          // execFile sets `killed` when it terminated the process on timeout.
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out fetching video info. Check the link or your connection.'
-            : cleanError(stderr) || err.message
-          resolve({ ok: false, error: msg })
-          return
-        }
-        try {
-          const data = JSON.parse(stdout) as RawInfo
-          if (data._type === 'playlist' || Array.isArray(data.entries)) {
-            const playlist = buildPlaylist(data)
-            if (playlist.count === 0) {
-              resolve({ ok: false, error: 'This playlist has no downloadable entries.' })
-              return
-            }
-            resolve({ ok: true, kind: 'playlist', playlist })
-          } else {
-            resolve({ ok: true, kind: 'video', info: buildInfo(data) })
-          }
-        } catch {
-          resolve({ ok: false, error: 'Could not parse video info from yt-dlp.' })
-        }
-      }
-    )
+  // `--` terminates option parsing so the URL can never be read as a flag.
+  const r = await execFileAsync(ytdlp, ['-J', '--flat-playlist', '--no-warnings', '--', target], {
+    maxBuffer: PROBE_MAX_BUFFER,
+    timeout: PROBE_TIMEOUT_MS
   })
+  if (!r.ok) {
+    const msg = r.timedOut
+      ? 'Timed out fetching video info. Check the link or your connection.'
+      : cleanError(r.stderr) || r.error?.message || ''
+    return { ok: false, error: msg }
+  }
+  try {
+    const data = JSON.parse(r.stdout) as RawInfo
+    if (data._type === 'playlist' || Array.isArray(data.entries)) {
+      const playlist = buildPlaylist(data)
+      if (playlist.count === 0) {
+        return { ok: false, error: 'This playlist has no downloadable entries.' }
+      }
+      return { ok: true, kind: 'playlist', playlist }
+    }
+    return { ok: true, kind: 'video', info: buildInfo(data) }
+  } catch {
+    return { ok: false, error: 'Could not parse video info from yt-dlp.' }
+  }
 }