**There is no spec for this yet.**
See original discussion in T7380. Currently, there's no convenient way to access threads other than the 6 you most recently participated in.
- The likely fix for this is a 7th `[...]` button which provides some options.
- However, exactly what lives there is murky. We should complete more features in the iteration before locking it down.
- We don't need to figure this out to test/develop the column, and it's a long way away from shipping anyway.