I was once taught that the definition of a tragedy was that it was inevitable. That the seeds of a character's end were there at the beginning. Well, if that is true, then it must apply to all characters, whether their outcomes are tragic or not.
This story is not a tragedy, but still I wonder if the ending of The Sauly Bird is predestined by the experience and motivations of the characters?
I think that the answer is 'mostly'. Although the inside story is not the whole story because of chance events, I think that it is the greater part.
As a writer, you realise that you're not god. Not all powerful, not even in a novel. Your characters are stubborn and they do what they want. The best you can do, I think, is to try and understand them.
I've come to the conclusion that it's impossible to disentangle the outside from the inside, but that it's essential to be aware of both. I can say a little about this in the cover letter but the synopsis is a different matter. As far as I understand, agents want a summary of the plot so the synopsis says very little about the inside story.
It's a nice description 'the inside story' implying that once you are aware of this, then the outside story will be immediately clear and comprehensible.