Joins phases 1 and 2 and covers phase 3's semantics. RoomTasksDataSource
implements all 14 seam methods; a StorageMode-routing delegate picks it
or the provider per call, since the mode is a setting the user can change
while the process lives.
There is no instances table, so a series is expanded at read time by
RecurrenceExpander and any RECURRENCE-ID override is substituted for the
occurrence it replaces. A timed series carries each occurrence's length
across; a due-anchored one has no start to offset from, so the anchor is
the due date — matching how the provider instantiated the same series.
Editing one occurrence writes a RECURRENCE-ID override sharing the
master's UID (RFC 5545 model (a)). The provider's Detaching.java forked a
brand-new task with its own UID instead — model (d), the one least
compatible with CalDAV. We inherited that without ever choosing it; this
is the choice.
TaskFormWriter states the completion rules directly instead of working
around the provider: progress and status now move together in both
directions, so a task can no longer strand itself "done at 75%".
TaskWriteMapper keeps the workarounds for External mode.
Deletes are hard when the list has no account and tombstones when it
does; master_id cascades, so a deleted series takes its overrides.
Jean-Luc Makiola
2e915da588