Opened the Harper Stash by casting Daylight (level 3) on the chest itself. Not the area effect, but "enchant item" option on the harper chest. Made the trap go away. Daylight level 3 is available from Shadowheart. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.