Share one iCloud among iPhone and iPad for Photos

I take pictures on my iPhone. I take pictures on my iPad. I make use of one AppleID. I configured my iPhone and my iPad to store the pictures on the iCloud.

1) Does Apple ensure that neither one overwrites the photo of the other?

In other words: if the iPhone saves a picture as IMG_0100.JPEG and iPad saves a picture as IMG_0100.JPEG afterwards, does the iPad picture overwrite the previously taken iphone-picture?

(I do not see any namespace concept)

2) If Apple ensure no overwrites, what is the logic?

Thank you