[Bug]: Sharing "task-only" calendars fails from Tasks page

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

To-do list sharing behaviour is inconsistent:

• In the Calendar view, it works
• In the Tasks view, it doesn't

Steps to reproduce

1. Create a new calendar that is only for VTODO items (not VEVENTS):
   • In a desktop/laptop web browser, go to your server's Tasks page (e.g. https://my.nextcloud.server/apps/tasks/ )
   • Click + Add List...
   • Type the name for your new todo list, such as test_list, and press the ↵ key on your keyboard
2. Click that new list's share icon (tooltip says "Share this list")
3. In the resulting Share with users or groups field, start typing the username of another user of your Nextcloud instance
4. Bug (unexpected result): no results are shown
5. You might think this means the list is simply not shareable, but...
6. In the same browser, go to your server's Calendar page (e.g. https://my.nextcloud.server/apps/calendar/ )
7. Mouse over the todo list you created earlier (e.g. test_list) and click the pencil icon (tooltip says "Edit and share calendar")
8. In the resulting Share with users or groups field, start typing the username of another user of your Nextcloud instance
9. The user is found, and the todo list can be shared with them.

Expected behavior

In the Tasks view, sharing the todo list should succeed just as it does in the Calendar view.

Nextcloud Server version

32.0.8.2

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

This is a hosted Nextcloud instance, so I cannot control which version of Nextcloud it runs. However, I have searched all bug reports and pull requests and did not notice any addressing this bug so presumably it is still a problem.

Start by reproducing the sharing search in the Tasks page and compare it with the working Calendar page. Trace the user-search request and handling from both entry points; the work is done when users can be found and a task-only calendar can be shared from Tasks as it is from Calendar.