Manually-added tags shouldn't all be removed when robodw (or whatever) adds one

[kaberett]

e.g. dreamwidth/dreamwidth#1466 should have retained all the tags rah added when I tagged it "curated: beginner", instead of losing them.

[kareila]

Although you make a good point, it's a bit of an edge case, in that most people will be adding all relevant labels at once - I think the curated labels are the only ones we would expect to be routinely added after the fact. But we should definitely think about the cases in which we want labels to be automatically removed at all - probably rarely if ever.

In the general case, we probably want all labels to be retained unless directly contradicted by a new label being assigned - e.g. if an issue labelled effort (1) gets a new comment adding effort (2), the effort (1) should be removed but any other labels should remain unchanged.

[kaberett]

So I'm pretty sure dreamwidth/dreamwidth#1509 (comment) also shouldn't happen - I want to be able to claim and tag something simultaneously rather than firing two notifs!