I think i also told them about wanting routing in the website notes section when i submitted the gerbers. I dunno if that's the correct way to do it, i wanted the fab house to do my pcb with rounded corners and they did exactly what i expected. Then on the 'fabnotes' layer i had text to say the boardoutline layer was to show the edge of the pcb for routing. So i made the track really thin, so it was more obvious that it was an outline rather than a router path. I wasn't sure if the outline track would be cut out with a router bit in the center (thus removing material ether side of the track center. Later on i added more tracks around my design (old ones had been deleted) I set these tracks to be on their own mechanical layer which i renamed to 'BoardOutline'. The first thing i did was to draw continuous tracks/arcs around my design to mark the shape i wanted, then i selected all these tracks/arcs and clicked the option to derive board shape from objects. I did the outline in altium designer before i generated the gerbers.

Altium designer board outline gerber