Obviously you should always expect the unexpected when taking on any serious home-improvement project, but … ugh. Balls. Some former owner put up cement board and linoleum panels rather than a proper shower liner; now that mold has set into the backing of the linoleum (which was obviously never supposed to be used in a shower environment), we had to pull down not only the facing, but also the cement board, in order to accommodate a new shower liner.
And behind the cement board was … this.
Cue the Scott “fix it knowing no one will ever see it” ingenuity/stupidity in 3, 2, 1 …