🖼️ fix: Show EMF/WMF Pictures in PowerPoint Previews

[TomasPalsson]

Problem

PowerPoint templates often store logos as EMF/WMF (Windows metafiles). pptx-preview turns them into data:image/x-emf URIs, which no browser can decode, so the logos render as broken images in the artifact preview. Seen with a customer template where 8 of 11 media files are EMF logos in the slide layouts.

Fix

• Server: extractPptxMetafileSvgs (new packages/api/src/files/documents/metafiles.ts) converts ppt/media/image*.emf|wmf to SVG with emf-converter (pinned 4.8.7, Apache-2.0, zero deps), keyed by an FNV-1a hash of the entry's base64. That is exactly what pptx-preview puts in img.src.

• html.ts: the map is embedded as <script id="lc-metafiles" type="application/json">, with < escaped. After the slides render, the iframe swaps matching <img> sources for the SVG data URIs. The swap is wrapped in try/catch and can never trigger the fallback.

• Budgets:

  • at most 64 metafiles
  • 5 MB per file
  • 8 MB of input in total
  • 3 s of conversion time
  • 256 KB per SVG, 384 KB of SVG in total

  If the map would push a deck over OFFICE_HTML_OUTPUT_CAP, the deck is retried without the map, so no deck that previews today regresses to the slide list.

• The CSP is unchanged (img-src already allows data:). The DOCX path is untouched.

Verification

• cd packages/api && npx jest src/files/documents src/files/code: 18 suites, 536 tests passing, 9 of them new.
• tsc, eslint and prettier are clean on the touched files.
• Checked in a browser with Playwright against the real customer template, via the storage-backed shell path: before, 3 broken <img>; after, 3 loaded SVG logos.

Not covered

• EMF used as a CSS background or fill. Only <img> is swapped.
• EMF+ records that need @napi-rs/canvas. These are skipped, not broken.
• DOCX.

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[TomasPalsson]

Superseded by LibreChat-AI#16672, which is now the source of this change. The squashed commit from that PR is cherry-picked onto sync/v0.8.8-rc4 directly.