Djibouti negotiations between Barre and Mengitsu was due to the pressure they faced from rebels. So they reached a compromise to stop supporting the other's rebel groups.
NFD was more sneaky he needed to secure his southern borders and support his crumbling government so he signed off NFD.
Arusha accord between Somalia & Kenya is what facilitated the coup later. It was meant for de escalation opening of roads, flights and agreement to solve NFD dispute in peaceful means. Even though Somalia did not gave up it's claims it was seen as treason by the people and apposition used it extensively to discredit the government who was already seen as corrupt.
When coup happened bo body resisted as the government largely fell off in favour of Barre's military government which made it a top priority.
