graph is walked out of order

[BrianHicks]

Take a graph. Call two modules in the root, and have one depend on the other.

What should happen

The tasks in the depending module should be executed after all the tasks in the dependent module.

What happens

All the tasks are executed at once, meaning that dependencies are not in place when the tasks are executed.

Concrete Example

application starting based on Docker. Top-level module depends on Docker, but it's not up yet when the leaf tasks start executing.