strawman attempt at a static-first runestone multiplechoice interactive

[StevenClontz]

WIP draft PR based upon discussions with @oscarlevin in mathtech discord.

Following is the LLM summary of this proposal. I will review and update before marking as ready to review by others. A known deficiency as of this edit: this only touches exercises with choices, but there are several other semantically-described <exercise/>s that should have improved print-ready HTML for use in worksheet/handout print previews.

Static-first, JS-hydrated multiple-choice exercises

Summary

A <worksheet> is meant to be printed, but a multiple-choice <exercise>
(one with a <choices> block) was rendered straight to a Runestone-JS-only
skeleton — a bare <ul data-component="multiplechoice"> of answer/feedback
<li>s that only became a real question once Runestone's JS enhanced it at
runtime. Printing a worksheet goes through a client-side-only "print
preview" pass that swaps stylesheets and reflows content, but never touches
the DOM inside an exercise, and there's no XSLT-time "print mode" to branch
on, since screen and print share one DOM. The result: a printed worksheet
either showed nothing where the question belonged, or leaked the raw,
unstyled skeleton.

This PR reworks multiple-choice rendering, site-wide, into a static-first,
progressively-enhanced pattern:

• XSLT now always emits genuine, readable HTML — a statement plus a lettered
  list of choices — annotated with just enough data (data-correct, a
  .choice-feedback block) to rebuild the interactive widget later.
• On a normal page load, JS reads that static HTML, rebuilds the exact
  data-component skeleton Runestone expects, and explicitly hands it to
  Runestone via window.runestoneComponents.renderOneComponent() — the same
  entry point knowl.js already uses for interactives injected after page
  load, since Runestone's own automatic scan only ever sees markup that
  existed when it ran.
• On a print-preview page, or for any reader without JS, that hydration step
  never runs, so the plain static HTML is simply what's shown.

Worksheets get a working printed/no-JS fallback as the direct result of a
general fix, rather than a worksheet-specific special case — and every
multiple-choice exercise anywhere in a book now degrades gracefully without
JS, for free.

Before / after

Regular (interactive) view — unchanged from a reader's perspective:
Runestone's full widget, radio buttons, and "Check Me" button.

Print preview view — previously a dead or broken skeleton; now a clean,
readable, lettered list:

How it works

	Before	After
XSLT output	<ul data-component="multiplechoice"> skeleton, unusable without JS	Real <statement> + lettered <ol> of choices, readable as-is
Interactivity	Runestone's automatic page-load scan enhanced the skeleton in place	JS rebuilds the skeleton from the static HTML, then explicitly calls renderOneComponent()
Print preview	No special handling — showed the broken skeleton	Hydration is skipped entirely; static HTML is what prints
No-JS fallback	Broken, unstyled skeleton with feedback text exposed	Same readable static HTML as print preview

Files changed

• xsl/pretext-runestone.xsl — the multiple-choice templates now
  hand-author static HTML (statement, lettered <ol> of choices,
  data-correct, a .choice-feedback block gated by the same
  $b-has-solution switch used everywhere else) instead of the
  JS-dependent skeleton.
• xsl/pretext-html.xsl — forwards the already-computed
  $b-has-solution flag into the template above.
• js/pretext_add_on.js (+ regenerated js/dist/pretext-core.js) —
  new hydrateMultipleChoice(), called from the existing DOMContentLoaded
  handler whenever the page isn't a print preview; rebuilds the interactive
  skeleton in place and hands it to Runestone via renderOneComponent().

Testing

Verified end-to-end against a real build (Saxon + the modified core, served
locally) with a headless-browser check:

• Interactive page: hydration runs, Runestone fully initializes the
  widget (class="... runestone-component-ready"), radio buttons render,
  MathJax typesets, and clicking an answer + "Check Me" correctly reveals
  the matching feedback ("✔️ Correct, 7 is prime.").
• Print preview page (?printpreview=<id>): hydration is skipped, no
  data-component anywhere, no radio buttons — just the plain lettered
  list.
• JS disabled: same plain, readable list as print preview — no blank or
  broken output.
• Solution-visibility publisher switches (common/exercise-worksheet,
  exercise-divisional, etc.) correctly gate whether .choice-feedback
  starts hidden, reusing the existing mechanism rather than inventing a new
  one.
• Zero console/page errors in either view.

Scope

Multiple-choice (choices) only, matching the original ask. Other
Runestone interactivity types (truefalse, parson, matching, etc.) are
unchanged and out of scope for this PR.