In T182548: Interaction Timeline returns only partial results on complex queries we discovered that we had exceeded the use case of the current Usercontribs API. We're also making hundreds/thousands of unnecessary requests.
Add a param to specify the other user(s) (single user for now, multiple users possibly later) who must have edited the page to include in the query.
User:Apples edits Bananas, Oranges, and Cucumbers
User:Bananas edits Bananas, Avocados, and Oranges.
If I request the user contribs of User:Apples, I should be able to specify that I only contribs that are to pages that User:Bananas has edited. In that case I would get all of User:Apples contribs to Bananas and Oranges, but the contribs to Cucumbers would be excluded.
Create Your Own API™ in T185459: Create user interaction endpoint