Thanks @Starfia, this appears to be a bug. Thanks very much for confirming that – at least it quiets my indecision about how to proceed. That advice just gives me a Content View that conforms to the detail column's resizable area, though, so I don't think it gives me the fixed-sizedness I'm looking for. The closest I've been able to come has been to hard-code the frame of the Navigation Split View itself, but that involves knowing the combined height of all views I might add to the detail column at all times (alongside which the unwanted safe area propagation persists), so it's a whole undertaking. I think for this iteration, I just have to avoid using NavigationSplitView or the Inspector; I have to implement alternatives to those provided functionalities, but the layout issues disappear the moment I sidestep them.
Topic:
UI Frameworks
SubTopic:
SwiftUI
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