Run 10537 reached node boot but the simulator crashed again at Graph
construction: lib/gui.py move_figure() unconditionally touches the Tk window
manager (canvas.manager.window), which does not exist under Agg. Patch it to a
no-op guard alongside the TkAgg->Agg backend swap. Also feed the simulator's
interactive cmdloop from a FIFO held open until teardown — CI stdin is EOF, so
the sim would otherwise exit immediately after booting the nodes.
eric
eff352b2ea