Really nice — rolling the PDF writer by hand (raster XObject + per-page CM offset for pagination) and rasterizing via SVG foreignObject instead of pulling in html2canvas + jspdf keeps us dependency-free, which is exactly the right call for this project. The AppBindings interface + mock are both updated, both locales are in sync, safeExportFilename guards path traversal, and the honest note about the unrelated pre-existing test failure is appreciated.

Merging. Two follow-ups worth a quick pass later (neither blocks):

1. Surface export failures to the user. The whole export is wrapped in catch (err) { console.error(...) }, so on a user-initiated action a failure is invisible — they click Export and nothing happens. A small notice/toast on failure would fit our "don't silently swallow" stance.

2. Verify the foreignObject path on older WebKit + KaTeX. Rendering a cloned surface through <foreignObject> to canvas is known to go blank or drop external resources on older Safari/WebKit (we've been bitten on macOS ≤12 before), and KaTeX's woff2 fonts referenced from the inlined CSS won't be fetched inside the SVG sandbox, so math may fall back to box glyphs. Worth a spot-check on a mac build and, if it's an issue, embedding the KaTeX font as a data URL.

Thanks!