Thank you everyone - I think that this discussion has now successfully aired the underlying issues quite nicely, as well as a few quite workable ways to tackle this ‘gardening’ (and I feel heard).
However, I’m not sure a megatopic is the best way forwards for this; if we are maximally flexing Discourse features, then a Chat Channel with threading is a much better fit in my mind.
This sort of stuff is definitely ephemeral; once a ‘small thing’ is fixed, there is zero value in keeping a record of the fact on a Topic. Likewise, there would be no value in these trivial / gardening things turning up in search at all.
It would also make it a reasonably easy thing to find, and relatively unobtrusive. It would also allow a convenient emoji to mark when something was sorted. Maybe TL2 and above to keep it from cluttering things up for newbies?