DESIGN-ITERATION TOOL ONLY. Renders a single complete HTML document to a PNG image and saves it to disk, returning the file path (not the image data). Open/view that PNG file with whatever image-reading capability your agent has to check the design — this tool does NOT produce a .pptx and is NOT how a presentation gets delivered. Use it only to check how one slide looks while you're still tweaking its HTML/CSS. Once the user's slides are finalized, you MUST call build_pptx to actually produce the .pptx file — that is the only tool that creates a deliverable presentation file.

THE DELIVERABLE TOOL. Renders a list of complete HTML documents (one per slide) and assembles them into a single PowerPoint (.pptx) file written to disk, one image-backed slide per HTML input, in order. Call this — not preview_slide — whenever the user asks for a PPT/PowerPoint/presentation/apresentação/slide deck; the tool result gives you the saved file path to report back to the user.