contract validation in long chains

Contract validation across a chain like the following does not spot the promise in Promiser and raises an error about Expecter needing it.

`organize` -> `Promiser`, (`If` -> chain(`Expecter`))


```ruby
organize \
  Promiser.promising(:thing),
  self.if(
    :condition,
    then: ExpectingThing = chain
      'ChainedThings',
      Expecter
    ),
    else: SomethingElse
  )
```