I reached out to the author of fasmg WRT your post and circular dependency interest and he pointed me toward two posts that he wrote very specifically to explain what he believes is unique to fasm/fasmg and allows to handle circular dependencies of many kinds. [0] Types of multi-pass assembly, and [1] related pitfalls.
[0] https://board.flatassembler.net/topic.php?t=20249
[1] https://board.flatassembler.net/topic.php?t=21060