=== Problem to solve
The tool does not provide the users visual feedback if the tool has broken, is loading, or if the user has done something incorrect.
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=== Acceptance criteria
* In the same place as the loading indicator () display the following messages:
** If only one username has been provided, or if the wiki has not been provided — "Please provide two usernames and wiki to begin."
*** This can be displayed on the timeline by default as a zero state.
** If there are no edits to show but the users have interacted in the past — "These two users have interacted, but there are no edits to show during the selected date range."
** If the users have never interacted in the past — "These two users have never interacted on the selected wiki."
* Use a [[https://doc.wikimedia.org/oojs-ui/master/demos/?page=dialogs&theme=wikimediaui&direction=ltr&platform=desktop|quick alert]] dialog to display these errors:
** General timeout/failure
** Invalid date range (e.g. start date is 2017 while end date is 2016)
* Do not allow users to type in the Users input box if there are already two names
* TBD: Log the errors
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=== Notes
* The inputs already prevent selecting invalid usernames and wiki.