Can u respond with scurvy. Cutthroat to get rid of a chain attachment coming off the agenda?

Scurvy Cutthroat: "Response: After an opponent plays an attachment card, discard Scurvy Cutthroat from play (cannot be saved) to discard that attachment from play."

FAQ: "(4.4) "Play" and "Put into Play"
Character, Location, and Attachment cards are
“played” from the hand during the marshalling
phase, by taking a player action and paying
their gold cost."

Scurvy Cutthroat can only Respond when an attachment is "played." Attaching the chain attachment from the Agenda does not meet the definition of "play." So no, Scurvy Cutthroat cannot be used against chain attachments that come off of the Agenda - any more than Scurvy Cutthroat can be used against attachments that come out of Shadows (for pretty much the exact same reason).