Registered usernames that are duplicates or invalid should trigger aggressive warning

[holmesworcester]

We should validate that data written to the user table meets our criteria, and show an aggressive warning if it does not.

1. All users should validate that username entries are correct, by the same criteria as the registrar frontend (alphanumeric, character limits, etc.)
2. All users should validate that there are not duplicate username registrations.
3. Seeing a message from a user with a duplicate registration signed by the admin should trigger a warning, even if there is only one registration in the user table. This does not apply to unregistered users, or an unregistered user having the same name of a registered user. This aggressive warning should only show when we have two messages from registered users signed by different public keys with the same name.
4. The warning should show on startup or, in the future, whenever someone switches to the community.
5. The warning should include a "leave community" button.

https://www.figma.com/file/TV9pF84Ob8pLYRLu83gNol/Joining-when-owner-is-offline?type=design&node-id=311-6979&mode=design&t=eS9WDLYpQNod1Acl-4

[EmiM]

@holmesworcester

1. I don't see designs for this "prominent non-closeable warning banner". I only see designs for closeable modal.
   There is a comment Warn user of duplicate official name #1647 (comment) saying "I think it makes sense to redesign this to be an alert banner that displays all the time rather than a full screen thing. Or it could be a full screen warning followed by an alert banner that displays all the time. Let's knock this back to 'needs design' and move it out of the sprint.". Since this task is marked as duplicate of 119 and I don't see a redesign I assume that we still need a design and a decision.

2. [EPIC] User should be able to join when owner is not online (discuss together and close) #1340 (comment) You wrote that the modal should be displayed on every restart. I wonder about this case:

• New unregistered user joins but does not connect to owner, connects to other unregistered users
• Turns out that new user chose username that is already taken
• The unregistered user is marked as "duplicated", other users see the modal(?)
• The unregistered user can ignore the fact that has duplicated username or simply close the Quiet and never come back
• The rest of community will be receiving "WARNING" popup on each Quiet start up indefinitely?

3. What do I see as a user with duplicated username? Modal? Popup? Said banner (AD 1)?