For how much can I proceed with the Institute before the Railroad is angry?

I am with the Railroad so I don't want to really side with the Institute but I don't want to leave them yet either, as it might prove useful that I can access their HQ (spy-ish). Without giving any spoilers, can anyone tell me how much can I work with the Institute before the Railroad becomes my enemy? Or when that quest arrives, will it be very clear? For example with Institute vs. Brotherhood, it was.

One thing about Fallout and Bethesda RPGs in general that I don't like, they don't consider all the options for why you might be making a decision. I don't want to end up finding out that Bethesda never thought it could be for espionage reasons that a player decides not to leave the Institute for a while and then suddenly I am a permanent member of the Institute.

I will tell you that you are golden as long as you dont kill the railroad when father tells you to. Every moment up to that you will be okay as long as you inform the railroad on every main mission they have you complete. You essentially will never choose a side until you are ordered to exterminate the other