So, on the 5th time of asking due to glitches with the High Celebrant and the portals, I finally completed the Coup de Grace mission.
Watched the cutscenes, spawned back on the shore... No triumph. No ship. No opportunity to run it again as its locked out on the lure.
Really outdone yourselves on this one Bungie. This mission was an absolute mess.
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you have to talk to spider/crow to get the triumph.