Grace and timeout timers in runRenderTitleJob can call getTitle after
finish() tears down the hidden BrowserWindow, throwing in the main
process when the Artifacts page resolves many link titles concurrently.
The hidden BrowserWindow used by fetchLinkTitle to scrape page titles
had no will-download handler on its session. When a link artifact URL
responds with Content-Disposition: attachment, Electron fires will-download
and the file is saved for real — explaining the spurious download on the
Artifacts page.
Add guardLinkTitleSession() (parallel to the existing audio-mute guard for
#49505) that installs a will-download handler which immediately cancels
every download item on the hermes:link-titles session. Call it from
getLinkTitleSession() right after the request-type blocklist is wired up.
Tier-2 link-title resolution loads the URL in an offscreen BrowserWindow to
read its <title> when curl can't. That window was never muted, so pages that
autoplay media (e.g. YouTube `watch` URLs) leaked ~2s of audio every time a
session containing such links was re-rendered. Move the window creation into a
dedicated helper that calls `webContents.setAudioMuted(true)` immediately after
construction, so the offscreen probe can never emit sound.
Fixes#49505
