The installed app only handled mailto: and webcal: launches. The launch
consumer dropped files, and nothing could hand a File to the composer or
the import dialogs, because the pending mailto is JSON in sessionStorage.
- manifest: `shortcuts` named in the browser's language, `file_handlers`
for .eml, .ics and .vcf, and `share_target`, all with the base path and
per-domain branding. Lite's manifest is unchanged.
- `lib/launch-handoff.ts`: the one place files and links wait, in memory
and in the Cache API, so they survive a sign-in that leaves the page.
The desktop bridge can call the same functions, since launchQueue never
fires in Electron. Sign-out clears it.
- launch consumer: routes files by type, and takes a shortcut to an open
window, which focus-existing would otherwise only focus.
- .eml opens in a new host for the preview, also before sign-in, with the
strictest device policy deciding about saving. .ics and .vcf open their
import dialogs through a new `initialFile` prop. A .ics needs the server,
so offline the dialog says so and carries on once back online.
- composer: `initialFiles` goes through `addFiles`, so plugin vetoes and
size limits still apply, also from a Pro compose tab.
- `sw.js` takes the share POST before the offline check and keeps the files
for the page. Without a worker, `/protocol/share` passes text and links
on and the page says the files are lost. `protocol` joins the app
sections and the handler pages join the shell, so a mailto: launch
offline no longer gets a network error.
Browsers without launchQueue or a service worker behave as before.