System Addressbook does not respect "Restrict users to only share with users in their groups" sharing option

Describe the bug

Hello team,
it's probably not considered a bug. But to operators like me, a serious issue.

I've just noticed that a system address book has been introduced some versions ago. Generally, I appreciate this feature. There is just one thing that annoys me on it: It doesn't respect the setting "Restrict users to only share with users in their groups.". This option has also limited the visibility of users that aren't within the same groups. This is a serious privacy setting on some of the instances that I manage. It's the only way to isolate core members from guests. Now with the system address book, it's suddenly possible to discover all other users again.

Steps to reproduce

Have two groups of users and the setting "Restrict users to only share with users in their groups." enabled.

Expected behavior

From my point of view, there should be one of these two options. The system address book …

• … can be disabled globally
• … respects the aforementioned setting

Actual behavior

Every user on the instance is visible in the address book.

Contact version

5.5.1

Operating system

27.1.3

PHP engine version

None

Web server

Apache (supported)

Database

MariaDB

Additional info

No response

Start by reproducing the issue with two user groups and "Restrict users to only share with users in their groups" enabled, then inspect the system address book behavior. Done means the address book either can be disabled globally or hides users outside the current user's groups while preserving the privacy setting.