These tests assert the behavior described at https://github.com/w3c/csswg-drafts/issues/11044#issuecomment-2599101601

Basic case: treat margins as 0.

When resolving stretch treat both block margins as 0 because the parent is not a BFC and has no top or bottom content edge (i.e. border + padding = 0).
But cyan's margins will not actually collapse through its IFC-siblings so there is overflow:

Parent has non-zero bottom border, so only top margin is treated as 0:

Parent has non-zero top padding so only bottom margin is treated as 0:

Account for the margins when parent establishes a BFC.