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When collapsed threads is enabled, notifications behave differently - see matrix of scenarios and associated outputs here (full spreadsheet of the chart below)
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Channel vs. Threads badges
In summary of the above chart:
when a root post with an @mention is posted in a channel, the mention badge is displayed on the channel, not the Global Threads sidebar item
When a reply post with an @mention is posted, the mention badge is displayed on the Global Threads menu item in the sidebar.
Channels vs. Threads unread state
When a reply is posted on a root post that has a mention, the mention badge stays on the channel that has the root post, BUT the Threads view now displays as bolded with a new unread message in a thread you follow
Other Implications to existing features (webapp)
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