Include mini apps to open links [Protocol handlers, exchanging data between webxdc]

Let me address your individual questions separately.

  1. The calendar webxdc app already supports importing a .ics file. Instead of clicking on the .ics attachment, export it as a file on the device from the timeline, open the calendar app, and then browse the file from the file picker to put it into your calendar.

  2. One may consider proposing to declare in the webxdc manifest any protocol handlers it can define. Then subject to confirmation on first use in DC, it could apply to either intents coming from the same group, same profile or anywhere within DC.
    protocol_handlers - Web app manifest | MDN

  3. One may consider a feature request for DC clients to declare serving OS-level protocol handlers backed by webxdc selected by the user.