You can't retcon safe composability onto a software system.

Composability is what allows building blocks to nest within each other to create a whole larger than the sum of its parts.

Composability can be a dangerous operation when the components are untrusted.

The lower the friction, the more dangerous the composition can be in a naive system.

You cannot simply retcon safe, low-friction composability onto a system after the fact.

I've talked to a number of very smart folks building frameworks for 3P agents to cooperate.

I asked them how their security model worked to allow untrusted 3Ps agents to participate.

They told me "oh we'll figure that out later".

To which I replied, "...no you won't!"

The only way to have a system with safe, low-friction composition is for it to have that property from the beginning and then never lose it as you grow and extend the system.

The web has maintained a security model of "clicking a link should never be directly dangerous" and "same origin isolation" since the beginning, allowing safe composition.

App frameworks don't have any similar general purpose primitive.