Do we still need buildSyntheticPageMapIfNoneDocumentProvided?

I thought I would remove them later, so there's no risk if this is being bumped into frontend soon and your PR coming only later. They are user patches using it in the wild :)
Unless you think I should ? (And you provide a way for these user-patches to not crash ?)

We can keep CreDocument:buildSyntheticPageMapIfNoneDocumentProvided() and substitute the call in it.

CreDocument.buildSyntheticPageMapIfNoneDocumentProvided = CreDocument.buildSyntheticPageMap

Together with adding the new methods.

It would replace real pagemap with synthetic one for the people with the user-patch, wouldn't it ?
You'd need to quickly write a one that would work this evening so we can merge it in frontend (for you to advance on your work) without being able to test it.
Let's keep it and clean later ?

Let's keep it and clean later ?

Yes, agree.