ConstRenders NO chrome — no title, no buttons, no window. The host owns the page state (page /
onPageChange at the call site) and builds its action row from optionsForPage, which is
what lets the same pair live in a dialog today and a taskpane later.
A page turn HIDES, it does not unmount. Next/Back is one window changing what it shows, and everything the user built on the page behind it survives: the query, the category, the scroll position, and page 2's filled-in arguments. Re-mounting threw all of that away — going Back to refine a search landed on an empty box with the whole catalog under it.
What resets page 2 is therefore a different FUNCTION, not a page turn: it is keyed on the one it was opened for. That is also why it does not mount until the first Next — an argument form for every function arrowed past on page 1 would evaluate the whole time the user is still choosing.
The two pages of Insert Function, composed: pick a function, then fill its arguments.