hof/flow: ctrl+c behavior is not great, maybe we need error and final handlers for cleanup

[verdverm]

have a flow that does the following

1. docker-compose up (or similar)
2. watch { hof gen & npm run dev}
3. ctrl-c (when done working)

I'm nor sure what happens to the the watched processes, in terms of signal value propagation and graceful shutdown.

Also, it is not possible to run docker-compose down

Another example:

1. build & start server
2. run tests, [error] experience test failure
3. [does not run] stop server

Probably the same issue if the tests were manually cancelled with a ctrl+c

So what we want is...

error and final handlers at the flow level to start ( maybe we can have a block or scope level latter, as part of a generalization )

so that we can

• do analysis & cleanup on error
• tear down on interrupt or completion

should there be a similar setup handler or phase, similar to teardown?