* fix(caldav): pull Google Calendar events from the events collection, not the /user principal
Google serves its CalDAV principal at .../caldav/v2/<id>/user but events live
under .../caldav/v2/<id>/events. The caldav library's principal->home-set
discovery does not reliably enumerate calendars from Google's /user endpoint,
so _sync_blocking fell into its 'treat the URL as a single calendar' fallback
and ran every calendar-query REPORT against the principal URL. /user holds no
VEVENTs, so the REPORT returned a clean but empty 200 for every date range:
auth succeeded, the calendar stayed empty (Apple Calendar works because iCloud
exposes standard discovery at the pasted URL).
Add _google_caldav_events_url() to map a recognised Google principal URL to its
events collection, and route both discovery-less fallbacks through
_open_url_as_calendar() so Google syncs hit /events while other servers' URLs
are used unchanged.
Fixes#2507
* fix(caldav): also map Google's legacy www.google.com/calendar/dav principal URL
Some Google accounts authenticate against the older CalDAV endpoint
(https://www.google.com/calendar/dav/<id>/user) rather than the newer
apidata.googleusercontent.com/caldav/v2 form (reported on #2507). Both have the
same principal-vs-events split, so map the legacy /user URL to its /events
collection as well. The legacy branch is gated on the /calendar/dav/ path so an
unrelated www.google.com URL ending in /user is left untouched.
The CalDAV pull prunes events in the synced calendar+window whose UID the
server didn't just return, to propagate upstream deletions. But CalendarEvent
had no field distinguishing a server-pulled row from a locally-created one, so
the prune also deleted events that were never on the server: events created by
the agent / email triage (which never write back to the server) and UI events
whose best-effort write-back failed. Result: silent, unrecoverable loss of the
user's appointments (hard db.delete, no soft-delete).
Add an 'origin' column to calendar_events (lightweight idempotent migration,
mirroring _migrate_add_calendar_is_utc), set origin='caldav' on rows the sync
inserts/updates, and gate the prune on origin == 'caldav'. Locally-created
events carry origin NULL and are never pruned. On the first sync after the
migration nothing is pruned (all rows NULL until re-marked), erring toward
keeping data.
Fixes#2704
L1