update

Replaces the contents of the frame handle refers to, in place — keeping its position, and thus its precedence, in the stack. Use this instead of remove + push when a still-mounted frame's scope/screen/section/parent changes: re-pushing would move the frame to the top and let it wrongly override inner frames that are still on the stack. A no-op (and no snapshot churn) if the contents are unchanged, the handle was already removed, or it belongs to another stack.

A parent that is this frame itself, or one of its descendants, cannot describe a real nesting and is refused: the frame becomes a root instead. See the note at the assignment below.

This revises scope/screen/section and the parent link only. It never clears a mask set by maskScreen, and never changes whether the frame is active — those are switches on the frame rather than part of the contents this replaces, and a pipeline revising a frame must not flip either of them by accident. Note the consequence while a frame is masked: a screen written here is stored but does not resolve, because maskScreen wins in recompute.

There is no way to un-mask, and remove + push is not one. Re-pushing is the very thing the paragraph above rules out: the replacement lands at the end of the list, so a container that un-masked this way would out-rank the inner frames its own content is still holding — measured, screen went to the container while its Detail content was on display. It also strands anything pushed with parent = the removed frame on a dangling link, which drops that subtree's scope entirely ({container, child} became {}). A surface that may name a screen must not mask in the first place; see maskScreen on why the switch is one-way.