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.
Verify createLinkTitleWindow mutes audio (regression guard for #49505) and
keeps the hardened offscreen defaults, and register the new test file in the
desktop platforms test script.
