Function below_the_floor 

fn below_the_floor(before: Option<&str>, held: &Held) -> Ask

Two cursor forms, one walk. The window’s newest page hands back the frame index its front sits at; every page below the floor hands back a row cursor (r:<byte>[:<id>]) minted from the row it reached. A frame cursor cannot be resolved to a row, because the frames the CLI streams and never writes sit between the window’s rows, so no arithmetic lines the two numberings up. It is answered from the window’s oldest row the file resolves instead: overlap at worst, never a gap, and a walk from any cursor converges on the same descending chain.