How do I set a "bounding" box to be written out in the GDS ? (Openlane is looking for

FIXED_BBOX

and not finding it in a manually drawn cell)

In magic (or at least in the open PDKs), the bounding box (abutment box) is translated from a GDS layer to a cell property (dictionary key:value pair) in magic (and back to a GDS layer when writing output). To set the bounding box, put the cursor box where you want the bouding box to be and type

property FIXED_BBOX [box values]

Thanks !