Summary

This PR enables the Microsoft Outlook (Office365) calendar cache to reduce the number of Microsoft Graph API calls when checking calendar availability on public event type pages.

Problem

Currently, for Microsoft Outlook calendars, Cal.com checks every single connected calendar whenever a user event type public page is visited. This works well for most cases but can become expensive as more calendars are added, especially for team events where multiple users' calendars need to be checked for round-robin scheduling.

Solution

This PR implements the following optimizations:

1. Enable Office365 Calendar Cache (CalendarCacheEventService.isCalendarTypeSupported)

The calendar cache was explicitly disabled for Office365 calendars. This change enables it:

static isCalendarTypeSupported(type: string | null): boolean {
  if (!type) return false;
  return ["google_calendar", "office365_calendar"].includes(type);
}

2. Expand Subscription to Individual Users (SelectedCalendarRepository.findNextSubscriptionBatch)

Previously, the subscription batch query only returned calendars for users in teams with the feature flag enabled. This change also includes users not in any team, ensuring individual users also benefit from cached calendar data:

// Include both:
// 1. Users in teams with the feature flag enabled (teamId in teamIds)
// 2. Users not in any team at all (to ensure individual users also get subscriptions)
const userTeamFilter: Prisma.SelectedCalendarWhereInput = {
  OR: [
    {
      user: {
        teams: {
          some: {
            accepted: true,
            teamId: { in: teamIds },
          },
        },
      },
    },
    {
      user: {
        teams: {
          none: {},
        },
      },
    },
  ],
};

How It Works

1. When the calendar-subscription-cache feature flag is enabled for a user, the CalendarCacheWrapper is used instead of the raw calendar service
2. The CalendarCacheWrapper.getAvailability() method splits calendars into two groups:
   • With sync: Calendars with both syncToken and syncSubscribedAt → served from the local database cache
   • Without sync: Calendars missing either → queried from Microsoft Graph directly
3. Microsoft Graph change notifications are used to keep the cache up-to-date:
   • When a calendar event changes, Microsoft Graph sends a webhook notification
   • The webhook handler processes the notification and updates the local cache
4. The cron job /api/cron/calendar-subscriptions periodically creates new subscriptions for calendars that don't have one yet

Testing

Updated the corresponding test to expect office365_calendar to return true for isCalendarTypeSupported.

Related Issues

• Fixes Outlook Cache – Bounty-to-Hire calcom/cal.com#21050
• Related: Microsoft Graph Outlook change notifications (https://learn.microsoft.com/en-us/graph/outlook-change-notifications-overview)