Care reminders can be handed to the owner’s calendar

A yearly vaccination reminder is where in-app scheduling is weakest. ADR-0003 already concedes that neither mechanism fires reliably on aggressive skins without a battery-optimisation exemption, and a WorkManager job is being asked to survive a year of reboots, an OS upgrade and possibly a new phone. The owner’s calendar is built for that horizon and syncs to their account, which makes it the only thing in this app besides a manual export (ADR-0005) that survives losing the phone.

Any care reminder therefore offers Add to calendar: Intent.ACTION_INSERT on CalendarContract.Events.CONTENT_URI with a title, an all-day begin time, and an RRULE matching the reminder’s repeat (FREQ=YEARLY for vaccination). No calendar permission is requested — the owner’s calendar app opens prefilled and they save it themselves.

This is additive, not a replacement. In-app reminders stay primary per ADR-0003, and the hand-off is offered per reminder, never done automatically. It applies to care reminders only: dose reminders keep exact alarms, because ADR-0003 gives them that path for a reason — a late dose has consequences, and a calendar entry is not an alarm.

Consequences

The app does not own the event. No event id is stored, so editing or deleting the reminder in-app leaves the calendar entry untouched, and completing a reminder ticks nothing off the calendar. The button must read as a one-way hand-off, not as syncing.

Tapping it twice creates two events. Record that a hand-off happened, so the button can say “Added to calendar” instead of silently duplicating.

ACTION_INSERT needs a calendar app installed. Guard the startActivity and fail with a message, not a crash.