Lumen slides export

lumen-slides-export

Export a lumen slide deck HTML to a fully editable .pptx file using Playwright + dom-to-pptx.

Tier: capability (atomic) — does not invoke other lumen skills. Composites and playbooks may invoke it.

When to invoke

Trigger phrases: export slides, slides to pptx, pptx export, powerpoint export, deck to pptx.

Pipeline

1. Verify HTML exists — confirm the slide deck HTML file path is valid.
2. Run CLI — invoke lumen-export-slides <html-path> (or npx lumen-export-slides <html-path> if local bin is not on PATH).
3. Report path — return the generated .pptx file path to the user.

Quality checks

• PPTX file is non-empty and readable by PowerPoint / Keynote / LibreOffice
• SVG diagrams (Mermaid, fgraph) are preserved as vectors when possible
• All slides from the HTML are represented in the PPTX

Validation (M02-S03)

The export pipeline now runs automatic validation in headless Chromium before conversion. Validation detects:

• Overflow — any element's bounding rect exceeds the 1280×720 slide bounds.
• Descender clipping — text nodes where bottom edge exceeds slide bottom with non-zero line-height variance.
• Unwrapped text nodes — bare text nodes directly inside .slide (not inside <p>, <span>, <h*>, <li>).
• Emoji usage — unicode emoji ranges in text content (PPTX compatibility risk).

Validation warnings are logged to stderr; export proceeds regardless (best-effort fidelity). Structural issues are reported immediately without retry. Transient failures (font loading, Mermaid rendering timeouts) retry up to 3 times with a 2-second delay.

CSS-to-PPTX bridging

• CSS scoping per slide — all stylesheet rules are prefixed with a slide-specific [data-slide-index="N"] selector before export to prevent class bleed across slides.
• Pseudo-element materialization — ::before and ::after pseudo-elements with non-empty content are converted into real DOM nodes with cloned computed styles before export.
• Canvas normalization — slides are forced to exactly 1280×720 pixels, 100vh/100dvh units are overridden, and scroll-snap/animations are disabled.

Known fidelity limits

The following features are deferred to future work:

• Google Fonts base64 embedding — current templates use system-font fallbacks.
• Baking CSS filter / opacity to canvas — niche use case, lossy, very complex.
• Auto-regeneration of slides on validation failure — validation reports issues; fixing them is the author's responsibility.

Output

Single .pptx file written alongside the HTML (or to --output if specified). Automatic versioning: if deck.pptx exists, creates deck_v2.pptx, etc.

Notes

• Playwright Chromium browser is downloaded on first run (~3 MB). If browser is missing, the CLI emits: run "npx playwright install chromium".