MGS9013: console not built
The server answered 400 bad request to a share request because it found no
built console, so a device opening the share link would load nothing.
[MGS9013] the built console was not found, so there is nothing to share; build
it with `magus run build console` and try again
see: .../MGS9013.md
Why
A share opens a LAN listener that serves the console app to another device.
The server looks for the build in MAGUS_CONSOLE_DIR, then in
<root>/console/gen, and needs an index.html there. Opening a listener with
nothing behind it would hand the other device a 404 in place of the app.
Resolution
Build the console with magus run build console, or point
MAGUS_CONSOLE_DIR at a directory holding a built console, then start the
share again. The server reads the directory when it starts, so restart it
after building: magus server stop, then magus server start.