revealjs preview↔render parity: footer/logo, section attrs, resources: VFS sync

claude-notes/plans/2026-06-17-revealjs-preview-render-parity-audit.md

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+# revealjs `q2 preview` ↔ `q2 render` parity audit
+
+**Created:** 2026-06-17
+**Epic:** bd-67yja58s (format: revealjs) · GA gate: bd-v053sk3s (Phase 1P)
+**Related strands:** bd-vv8jft5n (section-id + config parity), bd-qn8yi1su
+(automated golden parity test), bd-ocxnva1f (user Lua filters footer/logo)
+**Audit strand:** bd-zaa4m4bd
+**Footer/logo strand:** bd-n2w0sxgd (F3)
+
+## Overview
+
+`q2 preview`'s React `RevealDeck` (`ts-packages/preview-renderer/src/q2-preview/
+RevealDeck.tsx`) is supposed to produce the same DOM as `q2 render`'s native
+reveal scaffold (`crates/quarto-core/src/revealjs/assemble.rs`) for the same
+deck. This audit compares the two pipelines across `examples/presentations/*`
+and records every divergence so we can close them before the revealjs epic
+lands (the GA gate is bd-v053sk3s, "q2 preview shows an in-parity Tier-1
+slideshow").
+
+The investigation that seeded this plan compared `10-footer-logo` and
+`02-sections` empirically in Chrome (render served via `python -m http.server`
+over `slides.html`; preview via `q2 preview … --no-browser`), and cataloged the
+render-side `<section>` signatures for all 11 examples. Two divergence classes
+are **systemic** (every deck); one is **deck-chrome-specific** (only
+`10-footer-logo` today, but applies to any deck with `footer:`/`logo:`).
+
+## Findings
+
+### F1 — Section `id` dropped in preview (SYSTEMIC, partly tracked: bd-vv8jft5n)
+
+Render emits an `id` on every `<section>` (derived from heading text, or absent
+for `---`-only slides). Preview emits bare `<section>` with no `id`.
+
+| | render | preview |
+|---|---|---|
+| title slide | `<section id="title-slide" …>` | `<section …>` (no id) |
+| `## First topic` | `<section id="first-topic" …>` | `<section …>` (no id) |
+| `# Part One` stack | `<section id="part-one" class="section stack">` | `<section class="stack">` |
+
+**Impact:** breaks in-deck `#/id` deep links, cross-document anchors
+(`other.html#first-topic`), and any cross-reference whose target is a slide.
+bd-vv8jft5n already names this ("pass section ids onto `<Slide>`") but frames it
+as "minor" because hash-nav is off in preview — cross-doc anchors make it not
+minor.
+
+### F2 — Section semantic classes dropped in preview (SYSTEMIC, tracked: bd-vv8jft5n)
+
+Render puts `section` on every `<section>`, and `section title-slide center` on
+the title slide. Preview emits only the classes reveal.js itself adds at runtime
+(`present` / `future` / `stack`). The Quarto-authored classes are gone.
+
+| logical slide | render `class` | preview `class` |
+|---|---|---|
+| title slide | `section title-slide center present` | `present` |
+| content slide | `section future` | `future` |
+| section divider stack | `section stack present` | `stack present` |
+
+**Impact:**
+- `center` drives reveal's vertical centering of the **title slide** — its
+  absence visibly shifts the title-slide layout.
+- `title-slide` is a theme-CSS hook (Quarto reveal theme keys off it).
+- `section` is the generic slide-content hook.
+- Any author-supplied per-slide class (`## Slide {.smaller}`,
+  `{background-color="…"}`, etc.) rides the same `Attr` and is **also** dropped
+  — so F2 is broader than the three built-in classes; it is "the section `Attr`
+  is never forwarded onto `<Slide>`/`<Stack>` at all."
+
+F1 and F2 share one root cause and should be fixed together (likely folded into
+bd-vv8jft5n with its scope widened from "section-id" to "section `Attr`").
+
+### F3 — Deck-level footer / logo absent in preview (`10-footer-logo`, tracked: bd-n2w0sxgd)
+
+Render (`assemble.rs::render_revealjs_document`) places, as **direct children of
+`.reveal` outside `.slides`**:
+
+```html
+<div class="reveal has-logo">
+  <div class="slides"> … </div>
+  <img class="slide-logo" src="logo.svg">
+  <div class="footer footer-default">© 2026 … <a href="…">example.com</a></div>
+</div>
+```
+
+Preview emits none of these: no `.footer`, no `.slide-logo`, and `.reveal` lacks
+the `has-logo` class.
+
+**The data is already available to preview.** The reveal footer/logo render
+stage (`RevealFooterLogoTransform`, name `reveal-footer-logo`, selected by
+`pipeline.rs::footer_render_stage(is_revealjs=true)`) runs in the q2-preview
+pipeline — it is **not** in `Q2_PREVIEW_TRANSFORM_EXCLUDED` — so the preview's
+`ast.meta` carries `rendered.reveal.footer` and `rendered.reveal.logo`.
+`RevealDeck` simply never reads those slots, and the `<Deck>` wrapper never adds
+`has-logo` to `.reveal`. The fix is purely in `RevealDeck.tsx`: read the two
+meta slots and inject the markup outside `<Deck>`'s slides + add `has-logo`.
+
+**Impact:** decks with `footer:`/`logo:` show no footer and no logo in preview —
+a complete feature miss, not a style nudge. Tracked by **bd-n2w0sxgd**;
+`bd-ocxnva1f` covers *Lua filters* manipulating footer/logo, a different
+concern from this baseline "preview doesn't render them at all" gap.
+
+**Status (2026-06-17): DOM fixed and styled.** `RevealDeck` now emits the
+chrome. `RevealChrome` reads `rendered.reveal.{footer,logo}` and injects the
+markup into the `.reveal` element (outside `.slides`) via `useReveal()` →
+`getRevealElement()`, plus `has-logo`. Verified in Chrome on `10-footer-logo`:
+`.reveal.has-logo`, `img.slide-logo` + `.footer.footer-default` are direct
+children of `.reveal`, not in `.slides`, footer link preserved, footer
+`position: fixed; bottom: 18px` and logo `position: fixed; bottom: 0; right:
+12px` (theme styling applies — see F4). Tests: `RevealDeck.integration.test.tsx`.
+**Caveat:** the logo *image* still 404s — see F5.
+
+### F4 — (RETRACTED) "Preview reveal theme omits the chrome CSS layer" — was a stale-WASM artifact (bd-d0f9xoa6, closed)
+
+Initially filed when the footer/logo measured `position: static` and the theme
+blob lacked `.reveal .footer`. **Not reproducible on a clean build.** That
+reading came from a binary whose embedded WASM theme artifact was stale (built
+via `cargo xtask build-q2-preview-spa` *without* a WASM rebuild — the
+stale-WASM-in-`q2 preview` trap in CLAUDE.md). After `cargo xtask verify`
+rebuilt the WASM, the runtime-delivered theme **does** contain the chrome rules
+and footer/logo are correctly `position: fixed`, stable across reloads and
+500 ms–5 s time samples. Lesson: always rebuild WASM (`npm run build:wasm` /
+`cargo xtask verify`) before judging a preview *styling* gap.
+
+### F5 — Logo image 404s in preview: asset walker misses meta-driven raw-HTML images (tracked: bd-k5rxujiy)
+
+With F3's DOM in place, the logo `<img class="slide-logo" src="logo.svg">` fails
+to load in preview (`naturalWidth: 0`). Network: `GET /logo.svg` → **200
+`text/html`** (the SPA shell) — `logo.svg` is not in the preview's served VFS
+asset set, so the catch-all returns `index.html`.
+
+**Root cause (confirmed):** the parent-side asset walker
+(`ts-packages/preview-renderer/src/q2-preview/assetWalker.ts::collectImagePaths`)
+collects **only AST `Image` nodes** (`obj.t === 'Image'`). The logo comes from
+metadata (`logo: logo.svg`), rendered by `RevealFooterLogoTransform` into
+`rendered.reveal.logo` as a **raw HTML `<img>` string** that `RevealChrome`
+injects via `dangerouslySetInnerHTML`. It is never an `Image` node, so (1) no
+blob URL is minted for it, and (2) the raw `<img>` bypasses the `<Image>` React
+component that rewrites `src` against the manifest. `ResourceCollectorTransform`
+is likewise a no-op in `vfs_root` mode (`resource_collector.rs:96`) by design —
+the walker is the producer in preview. Native render works only because
+`logo.svg` sits next to `slides.html` on disk.
+
+#### The fix is two independent layers
+
+The problem decomposes into "are the bytes available?" and "does the element
+that wants them actually get them?". These are separable and must *both* hold.
+
+**Layer 1 — get the declared bytes into the preview VFS.** Honor a document's
+front-matter `resources:` in single-file preview, the same declaration used for
+publishing. `crates/quarto-preview/src/config.rs::resolve_single_file_deps`
+(bd-9cyza5vy) already runs the real parse + include stages and collects image
+deps via `collect_referenced_asset_urls(blocks)`; document `resources:` plugs in
+right beside that, reusing the existing publish machinery —
+`project_resources::extract_resource_patterns(&doc.ast.meta, ["resources"])` +
+`expand_patterns(canonical_root, deck_dir_anchor, …, DocumentMetadata, Page)`
+(the same `expand_patterns` already used in that file for *project* `resources:`)
+— folding the resolved files into `SingleFileDeps.binary_files`. Properties:
+reuses publish semantics (declare once → publish + preview), handles globs, is
+format-agnostic (helps any single-file doc referencing assets the AST walker
+can't see: `logo:`, raw HTML, shortcodes, CSS `url()`), and is on-policy
+(`config.rs:122` already treats `resources:` as the sync upload trust boundary).
+**This is the cheap, clearly-worthwhile piece and is implemented under
+bd-k5rxujiy.** Bytes-in-VFS is *necessary but not sufficient.*
+
+**Layer 2 — serve those bytes to the raw `<img>`.** The logo is a raw
+`<img src="logo.svg">` injected by `RevealChrome`; it fetches `/logo.svg`, hits
+the SPA catch-all, and never passes through the `<Image>` component that swaps in
+blob URLs. Two ways to close it:
+
+- **(a) per-asset rewrite (targeted, no infra changes).** Two small steps, both
+  in `preview-renderer` TS:
+  1. *Walker collects the non-Image paths.* `assetWalker.ts` already builds
+     `manifest: { origPath → blobUrl }` by reading VFS bytes via
+     `vfsReadBinaryFile` and minting blob URLs. Extend `collectImagePaths` (or
+     add a sibling collector) to also gather `meta.logo` and/or `meta.resources`
+     path strings, so the manifest gains `{ "logo.svg": "blob:…" }`. (Keyed by
+     the **same** string that appears in the injected HTML — both come from the
+     `logo:` value the Rust transform emits verbatim, so they match; a test
+     should pin that.)
+  2. *Injecting slot rewrites against the manifest.* `RevealChrome` builds a
+     detached `<div>` from the raw HTML before appending. Add a pass:
+     `wrapper.querySelectorAll('[src],[href]')`, and for each, look the current
+     attr value up in the manifest (via `AssetManifestContext`, the same source
+     the `<Image>` component already uses) and rewrite to the blob URL when
+     matched; external/`data:`/`blob:` pass through. Best factored as a reusable
+     `rewriteAssetRefs(root, lookupAssetUrl)` so footer images / navbar logos get
+     it too. **Stays entirely inside `preview-renderer` — no hub-client, sync
+     server, or quarto-hub.com involvement.**
+- **(b) service-worker VFS-by-path server (general, future-proof).** Serve
+  `/logo.svg` straight from the VFS so *any* path reference resolves with no
+  rewriting (`resources:` becomes the allow-list that gates it). This is the
+  bd-msp0 epic — it **touches hub-client and the quarto-hub.com deployment**, so
+  it is deferred until we're ready for that surface.
+
+**Decision:** Layer 1 lands now (bd-k5rxujiy). For Layer 2 we go with **(a)** —
+the per-asset rewrite, contained to `preview-renderer` — *or* defer Layer 2
+entirely, because **(b)** the service worker pulls in hub-client + the
+quarto-hub.com deployment, which we are not ready to take on yet.
+
+## Root cause (F1 + F2)
+
+`RevealDeck.tsx` maps each section `Div` onto `@revealjs/react`'s
+`<Slide>` / `<Stack>` but passes only the Div's **children** (`div.c[1]`). The
+Div's `Attr` (`div.c[0]` = `[id, classes, kvs]`) is read **only** to flip the
+incremental scope (`SlideBody` inspects `sectionClasses` for
+`incremental`/`nonincremental`); it is never emitted onto the `<section>`.
+`@revealjs/react`'s `<Slide>`/`<Stack>` accept `id`/`className` props (they pass
+through to the rendered `<section>`), so the fix is to forward them. The native
+contract is `assemble.rs` (and the `RevealSlidesTransform` that produced the
+`Div(.section)` tree shared by both paths).
+
+## Render-side catalog (all 11 examples)
+
+Every example renders `id` + `section` class on every `<section>`; title slides
+get `section title-slide center`. Only `10` carries deck chrome. Feature markup
+present per example (candidates for feature-specific preview divergence still to
+verify):
+
+| example | special markup to verify in preview |
+|---|---|
+| 01-creating-slides | title slide (`center`) |
+| 02-sections | vertical `stack`s ✅ compared |
+| 03-fragments | `.fragment` spans + `fragment-index` |
+| 04-incremental-lists | incremental lists → `.fragment` |
+| 05-columns | `.columns`/`.column` flex layout |
+| 06-speaker-notes | `.notes` (does preview load the Notes plugin?) |
+| 07-asides | `.aside` |
+| 08-footnotes | per-slide footnote coalescing + `.aside` |
+| 09-themes | `theme:` selection (theme parity in_progress: bd-y259zb57) |
+| 10-footer-logo | footer + logo + `has-logo` ✅ compared (F3) |
+| 11-auto-stretch | `.r-stretch` auto-stretch |
+
+## Work items
+
+### Phase A — fix the two systemic + one chrome divergence (TDD per /preview-parity)
+
+- [x] **F1+F2: forward section `Attr` onto `<Slide>`/`<Stack>`** (bd-vv8jft5n).
+  DONE 2026-06-17 — `sectionAttrProps(div)` forwards `id` + joined classes;
+  `renderTopSection` spreads it onto each leaf/inner `<Slide>` and the `<Stack>`.
+  Verified in Chrome on `10-footer-logo`: title slide now
+  `id="title-slide" class="section title-slide center present"` and reveal
+  vertically centers it (`section top: 288.5px`, h1 `text-align: center`); other
+  sections gain ids + `section`. Tests in `RevealDeck.integration.test.tsx`.
+  **Known gap:** `@revealjs/react`'s `<Stack>` only accepts `className` (drops
+  `id`), so a `# Section`-divider stack's own `id` can't round-trip through the
+  component yet (inner vertical slides still get theirs). `kvs` (e.g.
+  `data-background-color`) not yet forwarded — defer to authoring features
+  (bd-bea550b0). Both noted on bd-vv8jft5n.
+- [x] ~~**F4: include the Quarto reveal chrome CSS layer in the preview
+  theme**~~ — RETRACTED (bd-d0f9xoa6 closed); was a stale-WASM artifact, the
+  theme is fine on a clean build.
+- [x] **F5 Layer 1: honor document `resources:` in single-file preview VFS**
+  (bd-k5rxujiy). DONE 2026-06-17 — `resolve_single_file_deps` expands
+  `meta.resources` into `binary_files` (reuses `extract_resource_patterns` +
+  `expand_patterns`; globs supported). Tests `single_file_deps_includes_declared_resources`
+  + `_glob`; E2E A/B via real `q2 preview` (`binary_count` 1 vs 0). Bytes-in-VFS
+  only — the logo still 404s until Layer 2.
+- [ ] **F5 Layer 2: serve the bytes to the raw `<img>`** — option (a) per-asset
+  rewrite in `preview-renderer` (walker collects `meta.logo`/`meta.resources`;
+  `RevealChrome` rewrites `src`/`href` via `AssetManifestContext`), OR defer
+  until the (b) service-worker path-server (bd-msp0, touches hub-client +
+  quarto-hub.com) is on the table.
+- [x] **F3: render deck footer/logo + `has-logo` in `RevealDeck`** (bd-n2w0sxgd).
+  DONE 2026-06-17 — `RevealChrome` + `revealChromeFromMeta` in `RevealDeck.tsx`,
+  7-case `RevealDeck.integration.test.tsx`, verified in Chrome. DOM-only;
+  styling blocked on F4.
+- [ ] **F4: include the Quarto reveal chrome CSS layer in the preview theme**
+  (bd-d0f9xoa6). Footer/logo emit but render `position: static` — the preview
+  theme lacks `.reveal .footer` / `.slide-logo`. Decide under theme-parity
+  (bd-y259zb57): compile `quarto-revealjs.scss` into the preview theme, or move
+  the theme-independent chrome rules into the static `quarto-reveal.css`.
+
+### Phase B — full per-example audit (the "other examples" sweep)
+
+For each example NOT yet compared (01, 03, 04, 05, 06, 07, 08, 09, 11): render →
+serve → `q2 preview` → Chrome DOM diff (the workflow in this plan's Overview).
+Record any new divergence class as a finding here and file a focused strand.
+Known suspects: `06-speaker-notes` (Notes plugin), `05-columns` (flex styles),
+`09-themes` (theme delivery — already in_progress under bd-y259zb57).
+
+### Phase C — lock it down
+
+- [ ] Land **bd-qn8yi1su**: automated render↔preview golden parity test (the
+  slides analogue of `/preview-render-parity`) covering the Tier-1 set, so Phase
+  2 authoring features extend it per feature instead of re-auditing by hand.
+
+## Verification recipe (used for this audit)
+
+```bash
+cargo build --bin q2 --release
+./target/release/q2 render examples/presentations/<ex>/slides.qmd
+(cd examples/presentations/<ex> && python3 -m http.server 8765 &)   # render
+./target/release/q2 preview examples/presentations/<ex>/slides.qmd --port 8766 --no-browser &
+# Chrome: compare http://127.0.0.1:8765/slides.html  vs  http://127.0.0.1:8766/?page=slides.qmd
+# preview DOM is inside an <iframe> — query iframe.contentDocument.
+```
+
+## References
+
+- Native reveal scaffold: `crates/quarto-core/src/revealjs/assemble.rs`
+  (`render_revealjs_document`, `footer_logo_html`, `has-logo`).
+- Footer/logo render stage: `crates/quarto-core/src/revealjs/footer_logo.rs`
+  (`RevealFooterLogoTransform` → `rendered.reveal.{footer,logo}`).
+- Preview deck: `ts-packages/preview-renderer/src/q2-preview/RevealDeck.tsx`.
+- Pipeline seam: `crates/quarto-core/src/pipeline.rs`
+  (`footer_render_stage`, `Q2_PREVIEW_TRANSFORM_EXCLUDED`,
+  `build_q2_preview_pipeline_stages`).
+- Epic plan: `claude-notes/plans/2026-06-08-revealjs-presentations.md` (Phase 1P).
+- Skill: `/preview-render-parity`.