This was revealed in 2015, in the book Into the Black, about STS-1.
The hardcover edition of Into the Black had the overall basics of the imaging effort, although not specific details. ... His new version of the story in the paperback edition indicates that the imaging attempt had been planned starting over a year before the flight.
That revised paperback edition was published in April, 2017:
The first flight of the space shuttle, 36 years ago today, .... Until now, few people knew the details of a secret effort to inspect Columbia during its two days in orbit using the KH-11 spy satellite. Writer Rowland White tells the story in this condensed excerpt from the new, revised edition of his history of STS-1, Into The Black, to be published by Touchstone on April 18.
The crew did know they were being observed by a spy satellite, but this was not discussed on open comms:
Among the handful of people at JSC briefed on the NRO’s involvement were the primary and backup shuttle crews, who were already training for the first flight. Invited into the vault, the four astronauts listened intently as The Plan was described in detail. After considering what was said, Columbia’s STS-1 Commander, John Young, asked: “Well, what do we have to do in all this?”
"Nothing really,” replied Ken Young, ‘Just perform the maneuvers and orientations we send up. And don’t ask anything on the open loop if some attitude change seems weird or unconventional.”
while NASA’s press kit explained that each day the “launch windows opened at local sunrise plus 45 minutes and are more than 6 hours in duration,” Lineberry and Young knew that, while in theory that was right, in practice there was almost no flexibility at all. The two of them had chosen the launch time of 0700 hours EST very specifically. It was when they had determined that the shuttle would have to launch in order to optimize the opportunities for the NRO to capture images of Columbia in orbit.