The Meridian
The Meridian is a Dereth-wide institution that formed when the drift outgrew any one town. It is older and far better resourced than four frightened tradespeople, and genuinely skilled with portal magic in a way they are not. It takes its name from the cartographer's sense: a meridian is the reference line you chart everything else against. The Meridian maps the drift and drags the most dangerous doors back onto lines it controls.
The blind cartographer
The load-bearing truth about the Meridian is this: it cannot see the Warp either. It counts the doors, charts them, re-plots the worst ones, and does the whole of it blind - the way a mapmaker can draw a coastline whose deep geology they will never understand. It manages the drift at the scale of a continent and still does not perceive the thing beneath it.
That is not a weakness in the Meridian; it is its shape. It can carry a capable, unseeing traveller all the way up to the threshold of sight - and then it cannot follow them across. A ladder that ends one rung below the roof. Whatever lies past it is reached by climbing past the Meridian, not by being promoted inside it.
In the world so far
The Meridian keeps its distance. Its one visible hand in the world is quiet: it stands behind the Driftwarden Provisioner in the Unbidden Doors, stocking a stall four townsfolk could never afford and letting them believe the goods are their own pooled savings. It pays, through the Driftwarden's Mark, for adventurers who keep the doors thinned - an errand it finds cheaper than answers.
Its class trainers are its first open service to travellers. See Class Trainers and Class Abilities.
"The Meridian keeps the rest, and the ledger I answer to is longer than mine." - the Provisioner, once, and only once.