Turbo's offline/service worker sets an x_user_agent cookie with the
original browser user agent. This ensures platform detection works
correctly for Hotwire Native apps where service worker requests may
not carry the overridden user agent header.
Yes, Platform Agent is overkill for just this but there isn't a one-size JS solution for updating both input placeholders and other HTML text and we're likely to need it later for other things like displaying platform-specific PWA prompts.