Go to https://tcvdijk.github.io/intermetro/web to run the prototype; a demonstration video is available on YouTube.
You can navigate the canvas by scrolling (on a mouse shift-scroll to pan horizontally but it works best with a trackpad), or by using the Navigate-tool and dragging the canvas (here, scrolling zooms). You can jump to a previous version of the drawing by double clicking the entry in the edit history (bottom left), or just view it by clicking on the thumbnail.
Some failed routings require the current tool to be re-selected or jumping back to the previous version in the edit history. It might be helpful to open the browser's console to notice when this is the case. The export and import functions can be used to store and load the current hint set. If the browser becomes too slow after multiple interactions (or if the prototype stops working due to a bug), exporting the settings, refreshing the page and importing them again should help.
Hold Q, W or E for various selection modes; to apply the Straighten Edge hint, select the tool, select a set of edges, and press Enter.