Clarification: Are Side Mission Cards Discarded or reshuffled?

By Baer, in Imperial Assault Rules Questions

Are Side Mission Cards of a Mission just played reshuffled in the Side Mission Deck or are they discarded?

The RRG only reads

After the introductory mission is resolved, shuffle the Side

Mission deck, draw two cards, and place these cards faceup
on the table. After each non-agenda side mission is resolved,
shuffle the side Mission deck, draw one card, and place this
card faceup on the table.

RRG page 19

"Return the mission card corresponding to the mission that was just resolved to the game box"

discarded

Edited by Roolakhol

Ah, general notes on post mission clean up. Thanks.