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/ytdlp.ts

@@ -1,7 +1,7 @@
-import { execFile } from 'child_process'
 import { existsSync, mkdirSync, copyFileSync } from 'fs'
 import { dirname } from 'path'
 import { getYtdlpPath, getBundledYtdlpPath, YTDLP_MISSING_MSG } from './binaries'
+import { execFileAsync } from './lib/exec'
 import { VERSION_TIMEOUT_MS, YTDLP_UPDATE_TIMEOUT_MS } from './constants'
 import { getSettings, setSettings } from './settings'
 import { shouldAutoCheckYtdlp } from './ytdlpPolicy'
@@ -34,33 +34,21 @@ export function ensureManagedYtdlp(): void {
 }
 
 /** Spawn the bundled yt-dlp and read back its `--version` for the Settings panel. */
-export function getYtdlpVersion(): Promise<YtdlpVersionResult> {
+export async function getYtdlpVersion(): Promise<YtdlpVersionResult> {
   const ytdlpPath = getYtdlpPath()
 
   if (!existsSync(ytdlpPath)) {
-    return Promise.resolve({
-      ok: false,
-      error: YTDLP_MISSING_MSG
-    })
+    return { ok: false, error: YTDLP_MISSING_MSG }
   }
 
-  return new Promise((resolve) => {
-    execFile(
-      ytdlpPath,
-      ['--version'],
-      { windowsHide: true, timeout: VERSION_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out running yt-dlp.'
-            : (stderr || err.message).trim()
-          resolve({ ok: false, error: msg })
-          return
-        }
-        resolve({ ok: true, version: stdout.trim() })
-      }
-    )
-  })
+  const r = await execFileAsync(ytdlpPath, ['--version'], { timeout: VERSION_TIMEOUT_MS })
+  if (!r.ok) {
+    const msg = r.timedOut
+      ? 'Timed out running yt-dlp.'
+      : (r.stderr || r.error?.message || '').trim()
+    return { ok: false, error: msg }
+  }
+  return { ok: true, version: r.stdout.trim() }
 }
 
 /**
@@ -69,13 +57,13 @@ export function getYtdlpVersion(): Promise<YtdlpVersionResult> {
  * yt-dlp.exe lives in, which holds for both the dev resources/bin checkout and
  * a per-user install; it would fail under a locked-down system install.
  */
-export function updateYtdlp(channel: YtdlpUpdateChannel): Promise<YtdlpUpdateResult> {
+export async function updateYtdlp(channel: YtdlpUpdateChannel): Promise<YtdlpUpdateResult> {
   // Validate against the channel allowlist BEFORE the value reaches `--update-to`.
   // That flag also accepts `OWNER/REPO@TAG`, which would download and install an
   // arbitrary binary over yt-dlp.exe — so an unrecognised value (e.g. forged by a
   // compromised renderer over IPC) must never be forwarded. (audit F1)
   if (!isYtdlpUpdateChannel(channel)) {
-    return Promise.resolve({ ok: false, error: 'Unsupported update channel.' })
+    return { ok: false, error: 'Unsupported update channel.' }
   }
 
   // Self-heal: restore the managed copy from the bundled seed before updating, so
@@ -84,29 +72,19 @@ export function updateYtdlp(channel: YtdlpUpdateChannel): Promise<YtdlpUpdateRes
   const ytdlpPath = getYtdlpPath()
 
   if (!existsSync(ytdlpPath)) {
-    return Promise.resolve({
-      ok: false,
-      error: YTDLP_MISSING_MSG
-    })
+    return { ok: false, error: YTDLP_MISSING_MSG }
   }
 
-  return new Promise((resolve) => {
-    execFile(
-      ytdlpPath,
-      ['--update-to', channel],
-      { windowsHide: true, timeout: YTDLP_UPDATE_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out updating yt-dlp.'
-            : (stderr || err.message).trim()
-          resolve({ ok: false, error: msg })
-          return
-        }
-        resolve({ ok: true, output: stdout.trim() })
-      }
-    )
+  const r = await execFileAsync(ytdlpPath, ['--update-to', channel], {
+    timeout: YTDLP_UPDATE_TIMEOUT_MS
   })
+  if (!r.ok) {
+    const msg = r.timedOut
+      ? 'Timed out updating yt-dlp.'
+      : (r.stderr || r.error?.message || '').trim()
+    return { ok: false, error: msg }
+  }
+  return { ok: true, output: r.stdout.trim() }
 }
 
 /**