Function flow_report 

pub fn flow_report(placed: &Placed) -> String

What beck explain flow prints: the graph as a graph, rather than the four names the one recognised topology had.

§4.7 asks beck explain to answer “why is this here” from the compiler’s own data. The old version printed a fixed four-line summary and one hard-coded sentence claiming there was exactly one tier crossing — true of the todo sketch and of nothing the general slicer now accepts. This prints what the slicer read.