fix(main): L136 — enforce incognito in main (no errorlog / toast / cookie leak)

Incognito lived only in the renderer (history skip), so a "private" download
still leaked in main: errorlog entries (title+URL), OS toasts showing the title,
and the signed-in cookies attached — the UI promised "no logging, no history, no
cookies" but only history held.

Plumb `incognito` through StartDownloadOptions and enforce it in main:
- logFailure skips the errorlog write (and the pre-spawn errorlog in ipc.ts).
- notify uses a generic outcome title and drops the detail body, so no title/URL
  lands in the Windows Action Center.
- both cookie sources (--cookies login jar, --cookies-from-browser) are withheld,
  so a private download can't be tied to the user's identity.

typecheck + 262 tests + eslint + prettier green.

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

src/main/download.ts

@@ -90,9 +90,12 @@ function send(wc: WebContents, ev: DownloadEvent): void {
 }
 
 /** Native OS notification on completion/failure, gated by Settings.notifyOnComplete. */
-function notify(wc: WebContents, title: string, body: string): void {
+function notify(wc: WebContents, title: string, body: string, incognito = false): void {
   if (!getSettings().notifyOnComplete || !Notification.isSupported()) return
-  const n = new Notification({ title, body, icon: getAppIconImage() })
+  // L136: an incognito ("private") download must not leak its title/URL into an OS
+  // toast (it persists in the Windows Action Center). Callers pass a generic outcome
+  // title for the private case; here we additionally drop the detail body.
+  const n = new Notification({ title, body: incognito ? '' : body, icon: getAppIconImage() })
   n.on('click', () => {
     if (wc.isDestroyed()) return
     const win = BrowserWindow.fromWebContents(wc)
@@ -106,6 +109,9 @@ function notify(wc: WebContents, title: string, body: string): void {
 }
 
 function logFailure(opts: StartDownloadOptions, title: string | undefined, error: string): void {
+  // L136: incognito downloads are never recorded — not even a failure entry, which
+  // would persist the title + URL in the user-facing diagnostics log.
+  if (opts.incognito) return
   addErrorLog({
     id: opts.id,
     title,
@@ -199,7 +205,9 @@ export function buildCommand(opts: StartDownloadOptions, cookiesFile?: string):
     proxy: settings.proxy,
     rateLimit: settings.rateLimit,
     aria2cPath,
-    cookiesFromBrowser: settings.cookieSource === 'browser' ? settings.cookiesBrowser : undefined,
+    // L136/M6: incognito attaches no cookies from the browser either.
+    cookiesFromBrowser:
+      !opts.incognito && settings.cookieSource === 'browser' ? settings.cookiesBrowser : undefined,
     cookiesFile,
     restrictFilenames: settings.restrictFilenames,
     downloadArchivePath: settings.downloadArchive ? getDownloadArchivePath() : undefined,
@@ -279,7 +287,9 @@ export function startDownload(wc: WebContents, opts: StartDownloadOptions): Star
   // yt-dlp reads --cookies once at startup; we delete it the moment the download
   // settles, so the plaintext never lingers at rest.
   let cookiesFile: string | undefined
-  if (getSettings().cookieSource === 'login' && hasStoredCookies()) {
+  // L136/M6: an incognito download attaches no saved login cookies (the UI promises
+  // "no cookies"), so it can't be tied to the user's signed-in identity.
+  if (!opts.incognito && getSettings().cookieSource === 'login' && hasStoredCookies()) {
     // Unique per spawn (not just per id): a retry/resume reuses opts.id, and the
     // superseded download's cleanupCookies() must not unlink the new spawn's jar.
     const tmp = join(tmpdir(), `aerofetch-cookies-${opts.id}-${++spawnSeq}.txt`)
@@ -390,7 +400,12 @@ function wireChildProcess(params: {
       const msg = `Download stalled — no activity for ${Math.round(STALL_TIMEOUT_MS / 60_000)} min. Stopped; retry to resume.`
       send(wc, { type: 'error', id: opts.id, error: msg })
       logFailure(opts, getTitle(), msg)
-      notify(wc, getTitle() ?? 'Download failed', msg)
+      notify(
+        wc,
+        opts.incognito ? 'Download stopped' : (getTitle() ?? 'Download failed'),
+        msg,
+        opts.incognito
+      )
     }, STALL_TIMEOUT_MS)
   }
   bumpWatchdog()
@@ -434,7 +449,12 @@ function wireChildProcess(params: {
     if (!rec.canceled && !rec.paused) {
       send(wc, { type: 'error', id: opts.id, error: err.message })
       logFailure(opts, getTitle(), err.message)
-      notify(wc, getTitle() ?? 'Download failed', err.message)
+      notify(
+        wc,
+        opts.incognito ? 'Download failed' : (getTitle() ?? 'Download failed'),
+        err.message,
+        opts.incognito
+      )
     }
   })
 
@@ -449,12 +469,22 @@ function wireChildProcess(params: {
     if (rec.canceled || rec.paused) return
     if (code === 0) {
       send(wc, { type: 'done', id: opts.id, filePath })
-      notify(wc, getTitle() ?? 'Download complete', 'Finished downloading.')
+      notify(
+        wc,
+        opts.incognito ? 'Download complete' : (getTitle() ?? 'Download complete'),
+        'Finished downloading.',
+        opts.incognito
+      )
     } else {
       const msg = cleanError(stderrTail) || `yt-dlp exited with code ${code}`
       send(wc, { type: 'error', id: opts.id, error: msg })
       logFailure(opts, getTitle(), msg)
-      notify(wc, getTitle() ?? 'Download failed', msg)
+      notify(
+        wc,
+        opts.incognito ? 'Download failed' : (getTitle() ?? 'Download failed'),
+        msg,
+        opts.incognito
+      )
     }
   })
 }

src/main/ipc.ts

@@ -111,8 +111,9 @@ export function registerIpcHandlers(getMainWindow: () => BrowserWindow | null):
   ipcMain.handle(IpcChannels.downloadStart, (e, opts: StartDownloadOptions) => {
     const result = startDownload(e.sender, opts)
     // Pre-spawn failures (missing yt-dlp.exe, bad URL, duplicate id) never reach
-    // download.ts's own close/error handlers, so log them here instead.
-    if (!result.ok) {
+    // download.ts's own close/error handlers, so log them here instead — unless the
+    // download is incognito, which is never recorded (L136).
+    if (!result.ok && !opts.incognito) {
       addErrorLog({
         id: opts.id,
         url: opts.url,

src/renderer/src/store/downloads.ts

@@ -114,6 +114,9 @@ export const useDownloads = create<DownloadState>((set, get) => {
         options: item.options,
         extraArgs: item.extraArgs,
         trim: item.trim,
+        // Carry the private flag to main so it also skips errorlog, notification
+        // detail, and cookies — not just the renderer's history skip (L136).
+        incognito: item.incognito,
         meta: item.probedMeta,
         collection: item.collection
       })

src/shared/ipc.ts

@@ -423,6 +423,13 @@ export interface StartDownloadOptions {
   formatId?: string
   /** whether the chosen format already includes audio (skips +bestaudio) */
   formatHasAudio?: boolean
+  /**
+   * Incognito ("private") download. Main enforces the promise the UI makes ("no
+   * logging, no history, no cookies"): it writes no errorlog entry, reveals no
+   * title/URL in an OS notification, and attaches no saved login / browser
+   * cookies — not just the renderer's history skip (L136 / M6).
+   */
+  incognito?: boolean
   /** per-download post-processing override; main falls back to settings defaults */
   options?: DownloadOptions
   /**