Deny to use stories with different actors in composition.

[proofit404]

It does not make sense to nest management stories if you are the user.

Stories not marked with any Actor could be nested into story with any actor.

from stories import Story, Actor, I

class Architect(Actor):
    ...

class Reporter(Actor):
    ...

class TrackIssueProgress(Story, Architect):
    I.do

class FetchIssues(Story, Reporter):
    I.do

TrackIssueProgress(FetchIssues())  # error

[proofit404]

Superseded by #723