Description
More generally there are three related scenarios:
A. Passively-rendered content being updated with new passively-rendered content
B. Passively-rendered content being replaced with new interactive content
C. Interactively-rendered content being preserved when passively-rendered ancestors are updated
This issue covers case A, which is needed for Blazor United.
Case B is out of scope for this issue because it's not required for Blazor United and is vastly more complex to implement (it involves some new way to render interactive content into a non-document buffer (e.g., a DocumentFragment) and migrate all possible kinds of internal interactive rendering state that background buffer into the real DOM elements). Case B is covered by #42561.
Case C is needed for Blazor United will be cheap to implement given that we already implement case A.