fix(preview): adopt main's reveal-theme-on-slides on rebase (bd-y259zb57) + pin with test

Rebasing onto main surfaced the one semantic conflict in entry.tsx: our
branch suppressed the compiled theme link on reveal decks (currentDocIsSlides/
setDocIsSlides), which main's bd-y259zb57 deliberately removed so the compiled
Quarto reveal theme applies to slides too. Adopt main's behaviour:
reconcileThemeLink() applies lastThemeCssUrl unconditionally; drop
currentDocIsSlides + setDocIsSlides and the now-dead onDocIsSlides prop/effect
in PreviewRoot. Pin it with a new fail-on-revert integration test that drives
a slides UPDATE_AST + UPDATE_THEME and asserts the data-q2-theme link IS
applied (RED under the old suppression, GREEN now).

Author: gordonwoodhull

crates/wasm-quarto-hub-client/Cargo.lock

@@ -35,9 +35,6 @@ be in reverse chronological order (latest first).
 - [`24df47d1`](https://github.com/quarto-dev/q2/commits/24df47d1): Revert the G8 marker-aware list resolution — it hijacked every tight list-item click/hover to the parent list (a tight item's text is a bare node, so text clicks also report `e.target===<li>`), breaking per-item editing. Tight list items hover/click as items again.
 - [`04440c47`](https://github.com/quarto-dev/q2/commits/04440c47): Add Playwright e2e spec: T13(c) crumb jump relands collapsed (proven RED-on-revert). (The G8 marker spec from this commit was removed in 24df47d1; the G6/G7 settle-gate e2e was omitted — that timing-race guard is bound deterministically at the jsdom tier, so a browser test of it would pass vacuously.)
 - [`5e20b96e`](https://github.com/quarto-dev/q2/commits/5e20b96e): G4/G11/G12: bare modifier keys no longer trigger expand-on-edit; a second click inside an open editor now expands it; overflow-y is now 'auto' only when content genuinely clips (no scrolljack on expanded/fitting editors).
-
-### 2026-06-16
-
 - [`63b463b6`](https://github.com/quarto-dev/q2/commits/63b463b6): Fix G3 ArrowDown on single-line tight list items: exclude paddingBottom from isOnLastVisualLine height comparison; add G1/G3 Playwright + jsdom tests (T18/T19/T21).
 - [`2efb0bde`](https://github.com/quarto-dev/q2/commits/2efb0bde): Fix dirty nest-in/out caret column to apply `prefixWidth` adjustment (Principle A), matching the clean path so the column lands at the same source position after a dirty round-trip.
 

hub-client/changelog.md

@@ -169,12 +169,6 @@ export interface PreviewRootProps {
      * `LOAD_CUSTOM_COMPONENTS`). Tests pass `{}` (the default).
      */
     customRegistry?: Record<string, React.ComponentType<any>>;
-    /**
-     * Optional callback called when the document format switches to/from
-     * slides. In production, `entry.tsx` passes `setDocIsSlides` to
-     * reconcile the Bootstrap CSS link. Tests can ignore it (default no-op).
-     */
-    onDocIsSlides?: (isSlides: boolean) => void;
     /**
      * Optional callback called when `scrollToAnchorInDocument` would be called.
      * In production, `entry.tsx` provides the real scroll logic.
@@ -1401,12 +1395,6 @@ export function PreviewRoot(props: PreviewRootProps) {
     const previewFormat = parsed ? extractMetaString(parsed.meta?.format) : undefined;
     const isSlides = previewFormat === 'q2-slides' || previewFormat === 'revealjs';
 
-    // Notify caller (entry.tsx) about format switch so it can reconcile the Bootstrap CSS link.
-    const onDocIsSlides = props.onDocIsSlides;
-    useEffect(() => {
-        onDocIsSlides?.(isSlides);
-    }, [isSlides, onDocIsSlides]);
-
     // Build SourceInfo-value index from the untransformed AST (Plan 2a).
     const sourceIndex = useMemo(
         () => buildSourceIndex(props.untransformedAstJson),

ts-packages/preview-renderer/src/q2-preview/PreviewRoot.tsx

@@ -0,0 +1,85 @@
+/**
+ * Iframe-side theme-on-slides behaviour (bd-y259zb57 parity).
+ *
+ * Unlike `entry.integration.test.tsx` (which mocks `createRoot` and only
+ * exercises the module-top `UPDATE_THEME` → `<link data-q2-theme>` path for a
+ * NON-slide doc), this test drives the REAL render path: a slides `UPDATE_AST`
+ * mounts the real `PreviewRoot` (so the active doc genuinely IS a reveal deck),
+ * then an `UPDATE_THEME` arrives. It pins the contract that the compiled theme
+ * link IS applied on a reveal deck, matching `q2 render`.
+ *
+ * Fail-on-revert: re-introducing the old slide-theme suppression (a
+ * `currentDocIsSlides` gate making `reconcileThemeLink()` call `applyTheme(null)`
+ * on slides) yields no `<link data-q2-theme>` → this test goes RED.
+ */
+
+// @vitest-environment jsdom
+
+import { describe, it, expect, beforeAll, afterEach, vi } from 'vitest';
+import { act } from '@testing-library/react';
+
+// RevealDeck (rendered when the AST is a slide deck) imports @revealjs/react
+// and the vendored reveal CSS — stub them so mounting is light in jsdom. Do
+// NOT mock react-dom/client: we need the real render so the active doc is a
+// genuine reveal deck when UPDATE_THEME arrives.
+vi.mock('@revealjs/react', () => ({ Deck: () => null, Slide: () => null }));
+vi.mock('../../../../resources/revealjs/reset.css', () => ({}));
+vi.mock('../../../../resources/revealjs/reveal.css', () => ({}));
+vi.mock('../../../../resources/revealjs/theme/white.css', () => ({}));
+vi.mock('../../../../resources/revealjs/quarto-reveal.css', () => ({}));
+vi.mock('katex/dist/katex.min.css', () => ({}));
+
+beforeAll(async () => {
+    // Side-effect import: registers the module-top message listener.
+    await import('./entry');
+});
+
+afterEach(() => {
+    document.head
+        .querySelectorAll('link[data-q2-theme]')
+        .forEach((el) => el.remove());
+});
+
+// A minimal slide-deck AST: meta.format = "revealjs" makes PreviewRoot's
+// `isSlides` true (extractMetaString reads MetaString.c), so the mounted doc
+// is a reveal deck.
+const SLIDES_AST = JSON.stringify({
+    'pandoc-api-version': [1, 23, 0],
+    meta: { format: { t: 'MetaString', c: 'revealjs' } },
+    blocks: [],
+});
+
+async function postMessageAndFlush(data: unknown) {
+    await act(async () => {
+        window.dispatchEvent(new MessageEvent('message', { data }));
+        await Promise.resolve();
+    });
+}
+
+function themeLinks(): NodeListOf<HTMLLinkElement> {
+    return document.head.querySelectorAll('link[data-q2-theme]');
+}
+
+describe('q2-preview/entry theme link on a slide deck', () => {
+    it('applies the theme link on a slide deck (no suppression)', async () => {
+        // jsdom has no #root by default; updateAst needs it to mount.
+        const root = document.createElement('div');
+        root.id = 'root';
+        document.body.appendChild(root);
+        try {
+            // 1. Slides AST → real PreviewRoot mounts → isSlides effect →
+            //    entry.setDocIsSlides(true).
+            await postMessageAndFlush({ type: 'UPDATE_AST', payload: { astJson: SLIDES_AST, currentFilePath: 'deck.qmd' } });
+            // 2. Theme arrives for the (slide) document.
+            await postMessageAndFlush({ type: 'UPDATE_THEME', cssUrl: 'blob:slide-theme' });
+
+            // The compiled theme MUST reach the deck (bd-y259zb57): one link
+            // carrying the url. (Pre-fix: suppressed on slides → zero links.)
+            const links = themeLinks();
+            expect(links).toHaveLength(1);
+            expect(links[0].getAttribute('href')).toBe('blob:slide-theme');
+        } finally {
+            root.remove();
+        }
+    });
+});

ts-packages/preview-renderer/src/q2-preview/entry-slide-theme.integration.test.tsx

@@ -246,29 +246,20 @@ function applyTheme(cssUrl: string | null): void {
     link.setAttribute('href', cssUrl);
 }
 
-// bd-ibqkf9ry: the HTML-theme (Bootstrap) CSS must NOT reach a reveal deck.
-// A deck ships its own complete CSS (`resources/revealjs/…`, imported by
-// `RevealDeck`), exactly like `q2 render`'s standalone deck — so leaking the
-// HTML theme (e.g. Bootstrap's `h2 { border-bottom }`) onto slides is a render/
-// preview divergence. `UPDATE_THEME` (theme bytes) and `UPDATE_AST` (which
-// reveals the format) arrive on separate messages in either order, so we
-// remember the last theme URL + whether the active doc is a slide deck and
-// reconcile: attach the `data-q2-theme` link only for non-slide documents.
+// bd-y259zb57: the `UPDATE_THEME` channel carries the active document's
+// *compiled theme*. For an HTML page that's Bootstrap; for a `format: revealjs`
+// deck it's the compiled Quarto reveal theme, delivered through the SAME
+// `css:theme:<fp>` → styles.css transport. Both must be applied as the
+// `<link data-q2-theme>` so preview matches render.
+//
+// (Previously this suppressed the theme link on slides, because the preview
+// only ever produced Bootstrap CSS — never the reveal theme — and reveal decks
+// fell back to a hard-coded stock `white.css` import in `RevealDeck`. That was
+// the centered/uppercase render↔preview divergence this strand fixes.)
 let lastThemeCssUrl: string | null = null;
-let currentDocIsSlides = false;
 
 function reconcileThemeLink(): void {
-    applyTheme(currentDocIsSlides ? null : lastThemeCssUrl);
-}
-
-/**
- * Record whether the active document is a reveal deck and re-reconcile the
- * HTML-theme link. Driven by the render component's `isSlides` effect, so a
- * format switch (html ⇄ revealjs) re-applies or removes the theme correctly.
- */
-function setDocIsSlides(isSlides: boolean): void {
-    currentDocIsSlides = isSlides;
-    reconcileThemeLink();
+    applyTheme(lastThemeCssUrl);
 }
 
 /**
@@ -354,7 +345,6 @@ function updateAst(payload: UpdateAstPayload) {
                 unlockNestingCursor={unlockNestingCursor}
                 nestedEditBuffers={nestedEditBuffers}
                 customRegistry={customRegistry}
-                onDocIsSlides={setDocIsSlides}
                 scrollToAnchor={scrollToAnchorInDocument}
                 onNavigateToDocument={(path, anchor) => {
                     window.parent.postMessage(