mara, reviewing PR#3780's showExpandDetails boolean prop: "you cannot
just add it like this - if we have more and more options there in
different places we will keep accumulating cruft in the shared
component." SettingsMenu now exposes a plain children slot instead;
the agent page owns its expand-tool-output row entirely (state,
storage, markup) in its own ExpandDetailsSetting component and passes
it in, so the shared component never learns that setting exists.
