How does Flutter's own reconciliation process actually properly determine whether an already existing StatefulWidget's own associated State object should genuinely be preserved or instead genuinely be completely discarded whenever that specific parent widget rebuilds?

When a parent widget rebuilds, Flutter determines whether to genuinely preserve an already existing StatefulWidget's own associated State object by carefully comparing the new widget's own specific runtime type and its own explicit Key, if any, against the previous already existing widget occupying that exact same specific position within the tree, and if both of these genuinely properly match, Flutter correctly preserves that existing State object completely intact, including all of its own currently held internal state, simply calling didUpdateWidget to properly notify it of the specific new widget configuration, whereas if either the type or the Key genuinely differs, Flutter instead properly disposes of that entire old State object completely and creates an entirely fresh brand new one instead.

// Same type, no key, same tree position: state genuinely preserved
// Different type, or a differing explicit key: state completely discarded and freshly recreated