Successful build - Chance fights ever on the side of the prudent.

Link to build: https://jenkins.wildfiregames.com/job/docker-differential/2849/display/redirect

That folder contains special entities for campaign maps.

They're less special than e.g. territory_pull_30.xml, which is used only in the campaign_test_map.xml scenario, yet it is not located in the campaigns/ folder.

they will be hard to identify and find in atlas

Just type campaign and all six will show up, this patch doesn't change that.

Even more, they are not exactly structures or regular units.

They inherit from template_structure.xml and template_unit.xml and don't really have any lines other structures or units don't have.

I agree with @Angen here, these entities are not really something similar to structures or units in the sense of those in the specific folders.
The fact that they inherit from template_structure and template_unit is rather arbitrary I'd say.

The fact that they inherit from template_structure and template_unit is rather arbitrary I'd say.

Is it? What makes it arbitrary?

these entities are not really something similar to structures or units in the sense of those in the specific folders.

Aren't they? If you open those templates, you'll see lines that units or structures have too, and no lines that structures or units don't have.
Moreover, maps/scenarios/campaign_test_map.xml contains a athen_support_trader and athen_campaign_city.xml can explicitly train more of those.

If you open them in Atlas one can clearly see they were not designed to be on the RTS map, but rather as entities on a campaign map ^^ As the tooltip of the "units" implies.

While campaign_city_test.xml and campaign_city_minor_test.xml indeed have an actor on a visibly different scale, campaign_religious_test.xml uses the same actor as the athen_temple.xml template. Anyway, actors are just art.
What should matter is their current function in game. These campaign entities have attack, health, territory influence, etc., like other structures and units.

I disagree with the change for the same reasons as Angen and Freagarach. IMO the only meaningful change we should make is: as part of D11, move the files we use to a new relevant place, and delete the others (moving them to the art repo). For instance the campaign test map should become an actual test campaign within the new campaign framework.