How does Flutter's own underlying constraint based layout system genuinely work, specifically regarding how constraints actually flow down the widget tree while sizes actually flow back up?

Flutter's own underlying layout system genuinely follows a specific well defined protocol where a parent widget passes down a set of constraints, meaning a genuinely allowed minimum and maximum width and height, to each individual one of its own children, and each individual child then genuinely determines its own actual specific size based on those particular received constraints together with its own particular intrinsic content, then properly reports that determined final size back up to its own parent, and importantly, a parent generally cannot actually know its own specific final size until every single one of its own children has already genuinely finished determining their own individual sizes first, a foundational underlying concept commonly summarized as constraints genuinely flow down while sizes genuinely flow back up.

// A parent widget cannot know its own size until its children
// have all genuinely finished determining their own individual sizes first