Bug: warning/error dialog box auto disappears even though it has an ACK button

If an invalid message ID is used (or the id is valid but the message is not available to the current user) then a message dialog box is shown with a green "Got it!" button.

For example:

https://lists.apache.org/thread.html/abcd@defg

This is confusing - why have a button if it is not needed?
Also the message may be missed if the user does not switch to the tab immediately.

The same applies to other error/warning dialogs, e.g. mixed public/private lists.

Reproduce the invalid or unavailable message ID case, then check the equivalent mixed public/private-list warning dialog. Trace the frontend dialog handling entry point, and confirm that each warning or error remains visible until the user activates the "Got it!" ACK button.

Written by the indexing model from the issue text.