feat: provide SCHEDULE-AGENT via ics patch

[laz-001]

What does this PR do?

There is a property (SCHEDULE-AGENT=CLIENT) a CalDAV client can add to the event that would prevent CalDAV servers from sending invitations.

This PR patches the used ics-2.37.0 to provide this functionality.

• Fixes #9485
• /claim #9485

Visual Demo

Mandatory Tasks

• [x] I have self-reviewed the code (A decent size PR without self-review might be rejected).
• [X] I have updated the developer docs in /docs if this PR makes changes that would require a documentation change.
  • N/A (I assume its autogenerated)
• [x] I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

Via API, local CalDAV

• I have validated the changes with the original tests in the ics repo-code (does not break anything)
• I have validated the changes within cal.com (does not break existent tests, new unit tests work as expected)
• I used the Cal.com API endpoint: http://localhost:3000/api/book/event with an admin API key to create an event with SCHEDULE-AGENT=CLIENT, which was correctly propagated to the local CalDAV server.

Via API, Remote CalDAV

( will tomorrow attempt with a remote CalDAV )

• create an event with SCHEDULE-AGENT=CLIENT
• verify the no duplicate email is sent

Via Collaboration

• If someone with a running setup could collaborate to test this quicker, would be nice.
• If someone could provide an e2e test (if project supports), would be excellent.

Via User Interface

My understanding is that this core/backend-level work needs to be complemented by UI work.

Not sure about this, but this could be the location to add a drop-down for SCHEDULE-AGENT

---

Summary by cubic

Added support for the SCHEDULE-AGENT property in calendar events by patching the ics library, allowing CalDAV clients to prevent servers from sending invitations.

• Dependencies
  • Applied a custom patch to [email protected] to support SCHEDULE-AGENT for organizers and attendees.

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[github-actions[bot]]

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 - revert: Reverts a previous commit

[graphite-app[bot]]

Graphite Automations

"Add consumer team as reviewer" took an action on this PR • (06/14/25)

1 reviewer was added to this PR based on Keith Williams's automation.

"Add community label" took an action on this PR • (06/14/25)

1 label was added to this PR based on Keith Williams's automation.

[laz-001]

@TusharBhatt1 , @PeerRich, contrary to #21095, this PR does not use an ics-fork, but an ics-patch. The implementation is different, too. Backend fix that must possibly be complemented/activated by a frontend addition.

[github-actions[bot]]

This PR is being marked as stale due to inactivity.