Popup a confirmation box when adding risky user to confidential issue

We should consider a feature to help prevent accidental tags on confidential issues. In many platforms something like this is common, for example when you are sending a meeting invitation in Gmail, if the user is not someone you have emailed before you get a popup confirming this is intended.

We could achieve this in a few ways:

• If the user is not at least a "Developer" in the group
• If you have never tagged that user before
• probably more

Design

To have users notice that they mention a person who doesn't have the permission to see the confidential issue:

• On "Write" tab, it has the person's permission level after the username.

• e.g. @username(guest).

• In the dropdown list of members, it has an eye-slash icon after the person's username.
• On "Preview" tab, the person's username has a red background(#FBE5E1).

Dropdown list	Write tab	Preview tab