Fix: non-destructive calendar updates, attendee support, RFC 5545 compliance

[JonathanGodley]

Summary

• Bug fix: updateCalendarEvent destroyed all non-standard properties (attendees, reminders, recurrence rules, X-GOOGLE-* etc.) by rebuilding VEVENT from scratch. Now patches in-place, preserving everything not explicitly changed.
• Bug fix: createCalendarEvent silently failed for all-day events (produced midnight UTC instead of VALUE=DATE)
• Bug fix: JMAP calendar handlers used a try/catch JMAP-then-CalDAV fallback pattern, but the JMAP Calendars spec (JSCalendar / RFC 8984) is not yet finalized and Fastmail has not enabled JMAP calendar support. The JMAP calendar code also has known bugs (participants sent as array instead of RFC 8984 object/map, startDate/endDate not passed through, participants: [] sent when none provided). Replaced with direct CalDAV calls; JMAP calendar code retained with bug fixes and TODO markers for when Fastmail enables support.
• Feature: Attendee/organizer parsing with PARTSTAT, ROLE, CUTYPE, RSVP
• Feature: Participant support on create and update (with email validation to prevent injection)
• Feature: Recurring event safety — confirmRecurring flag required for time changes, orphaned exceptions pruned via RRULE expansion
• Feature: DURATION parsing, timezone preservation, RFC 5545 compliance (SEQUENCE increment, LAST-MODIFIED, value type consistency)

What changed

src/caldav-client.ts (+966 lines)

• Non-destructive patch-based updates using line-based VEVENT editing with VALARM depth tracking
• New functions: parseAllICalProperties, parseAttendee, findValueBoundary (quote-aware), replaceICalProperty, removeAllICalProperties, insertBeforeEndVEvent, removeOrphanedVTimezones, removeExceptionVEvents, parseICalDuration, formatDateTimeProperty, validateAttendeeEmail, quoteParamValue, detectLineEnding, toICalUTC (with date-only guard), foldICalLine (with configurable line ending)
• extractVEvent returns null instead of full input when no VEVENT found (was silently parsing VTIMEZONE properties)
• Participant interface and CalendarEvent extended with organizer? and participants?
• parseCalendarObject takes optional { includeParticipants } (only get_calendar_event enables it, keeping list responses compact)

src/caldav-client.test.ts (+1475 lines, 171 new tests)

Comprehensive coverage including CRLF/LF preservation, VALARM sub-component skipping, injection prevention, recurring event orphan detection, quote-aware parsing, and all edge cases.

src/index.ts

• JMAP calendar fallback removed — CalDAV called directly with comment explaining why
• update_calendar_event and delete_calendar_event tool schemas and handlers added
• create_calendar_event now passes participants through to CalDAV (was silently dropped)
• get_calendar_event uses getCalendarEventById with participant parsing

src/contacts-calendar.ts

• Fixed participants: [] being sent when none provided (JMAP bug)
• Added TODO markers on known JMAP calendar issues

package.json

• Added rrule dependency for RRULE expansion during recurring event orphan detection
  • Single transitive dependency (tslib), built-in TypeScript types
  • Alternative: if this dependency is undesirable, the orphan detection can be replaced with "delete ALL exceptions on time change" (matching Google Calendar behavior). The code has a comment at the import explaining this tradeoff.

README.md

• Calendar known limitations section
• FASTMAIL_CALDAV_DISPLAY_NAME env var documented
• Updated tool descriptions

Supersedes

This PR supersedes #45 (iCal encoding fix) — those fixes are included and extended here.

Test plan

• npx tsc --noEmit passes
• All 171 new CalDAV tests pass (224 total pass; 3 pre-existing validateSavePath failures on Windows unrelated to this PR)
• npm run build compiles
• get_calendar_event on event with Google-synced attendees — participants visible with PARTSTAT/ROLE/CUTYPE
• update_calendar_event changing only title — attendees survive, timezone preserved, SEQUENCE unchanged
• create_calendar_event with participants — ORGANIZER and ATTENDEE lines present
• create_calendar_event with date-only start — all-day event, not midnight UTC

[JonathanGodley]

Couldn't see attendees, and that sent me down one hell of a rabbit hole when I found other issues.

Got everything working with CalDAV and intentionally disabled JMAP calendar support. Reasoning was that JMAP isn't actually supported by FastMail, existing implementation appears to have bugs, and when Fastmail DO enable support, significant testing and likely bugfixing will be required.

IMO - safer to explicitly disable it until the the JMAP implementation is enabled, so that it can be properly tested and feature parity can be ensured.

Tried to closely follow the RFC specs, or other existing implementations where possible.

As per the pull request - i have brought in an additional dependency to try and intelligently handle calendar entries in repeated series - but a workaround is feasible (albeit a bit of a blunt instrument).

[JonathanGodley]

Pushed a follow-up commit (de56612) addressing #56 and a related bug found alongside it:

• Empty-string overwrite (update_calendar_event silently overwrites fields with empty strings #56): title/description/location are now loud-rejected on empty/whitespace/null instead of silently blanking the property. A new clearFields array (description, location) handles deliberate deletion; setting and clearing the same field in one call is rejected.
• Orphaned ORGANIZER: participants: [] previously removed all ATTENDEEs but left a dangling ORGANIZER (a malformed scheduling VEVENT). It now strips ORGANIZER too, gated on the empty case so the participant-add path still emits one.

Both come with unit tests (the existing participants: [] test was flipped to assert ORGANIZER removal), and the validation helpers are self-contained in caldav-client.ts. Closes #56 when this merges.