feat(exporters): real PDF/PPTX/ZIP via system Chrome + pptxgenjs + zip-lib (lazy-loaded)

[hqhq1025]

Replaces the EXPORTER_NOT_READY stubs in packages/exporters/src/{pdf,pptx,zip}.ts with three lazy-loaded tier-1 implementations. Decisions locked in docs/research/04-pptx-export.md.

Stacks on top of #4 (wt/first-demo). Rebase or land that PR first; this branch contains the same commits plus one new commit on top.

Why each format works the way it does

PDF — puppeteer-core + system Chrome

• We refuse to bundle Chromium. PRINCIPLES §1 caps the installer at 80 MB; a Chromium download is ~150 MB.
• chrome-discovery.ts walks canonical paths per OS (Mac .app, Win %ProgramFiles%, Linux which) plus a CODESIGN_CHROME_PATH override.
• Throws CodesignError('System Chrome not found, install from https://www.google.com/chrome', 'EXPORTER_NO_CHROME') when nothing resolves — no silent fallback (PRINCIPLES §10).
• Tier 1: no header/footer, no font embedding, default Letter page format (auto available for tall single-sheet output).

PPTX — pptxgenjs only

• One slide per top-level <section>; whole document if no sections exist.
• We deliberately skip dom-to-pptx in tier 1 — unmaintained (last release ages ago), only adds value for the small set of layouts already covered by our regex extractor. Tier 2 can revisit.
• CJK fix: pptxgenjs defaults emit bodyPr wrap="square" and we explicitly set fit: 'shrink' (= normAutofit), sidestepping the dom-to-pptx CJK overflow bug from research/04 §"Known traps".

ZIP — zip-lib

• ~80 KB, MIT, zero deps. Stable archive layout: index.html at root, README.md (generated banner with timestamp + restore instructions), optional assets/ subtree.
• Staging directory pattern so Zip.addFile always points at a real file path (zip-lib's API takes disk paths, not buffers).

Files

New

• packages/exporters/src/chrome-discovery.ts + .test.ts (6 cases: mac path, win ProgramFiles, linux which, override, missing, linux-missing)
• packages/exporters/src/pdf.test.ts (3 cases — happy / override / wrapped failure, all puppeteer mocked)
• packages/exporters/src/pptx.test.ts (6 cases incl. real CJK end-to-end write that produces a valid .pptx on disk)
• packages/exporters/src/zip.test.ts (3 cases incl. multi-asset round-trip via Unzip)

Modified

• packages/exporters/src/{pdf,pptx,zip}.ts — real impls
• packages/exporters/src/index.ts — isExporterReady flips to true; dispatch passes htmlContent + destinationPath
• packages/exporters/package.json — three new prod deps
• apps/desktop/src/main/exporter-ipc.ts — comment refresh; routing already supported all four formats
• apps/desktop/src/renderer/src/components/PreviewToolbar.tsx — ready: true on PDF/PPTX/ZIP; tooltips describe what each format produces

New production dependencies

Package	License	Disk size (du -sh)	Lazy-load proof
puppeteer-core@^24	Apache-2.0	12 MB	await import('puppeteer-core') inside exportPdf body
pptxgenjs@^3.12	MIT	2.6 MB	await import('pptxgenjs') inside exportPptx body
zip-lib@^1.0.4	MIT	100 KB	await import('zip-lib') inside exportZip body

$ grep -nE "await import\('(puppeteer-core|pptxgenjs|zip-lib)'\)" packages/exporters/src/*.ts
packages/exporters/src/pdf.ts:31:  const puppeteer = (await import('puppeteer-core')).default;
packages/exporters/src/pptx.ts:32:  const PptxGenJS = (await import('pptxgenjs')).default;
packages/exporters/src/zip.ts:54:  const { Zip } = await import('zip-lib');

All three are runtime deps but live entirely outside the cold-start module graph — the renderer never touches them, and the main process only resolves them the first time the user clicks Export → {PDF|PPTX|ZIP}.

Install size

du -sh release/ was not measured because the desktop build pipeline is a follow-up (no electron-builder config landed yet in this worktree). The on-disk dep contribution is bounded above by du -sh node_modules/.pnpm/{puppeteer-core,pptxgenjs,zip-lib} = 14.7 MB unpacked. After Electron asar packing + tree-shaking on import-time-only modules, expect ≤ 6 MB shipped. Re-confirm in the install-size CI gate once it's wired.

Acceptance test outcomes

1. PDF — pnpm dev → Export PDF → opens in Preview/Acrobat (manually verified locally on macOS with installed Chrome)
2. PPTX — opens in Keynote and PowerPoint Mac with text editable; npm vitest run packages/exporters/src/pptx.test.ts confirms PK\x03\x04 magic bytes + bytes > 1 KB
3. ZIP — Unzip round-trip in zip.test.ts confirms index.html, README.md, and assets/* are all present
4. CJK — pptx.test.ts writes <section><h1>你好世界</h1><p>第一张幻灯片</p></section> to a real file; manual PowerPoint Mac open shows no overlap
5. No-Chrome — chrome-discovery.test.ts "throws EXPORTER_NO_CHROME with install link" passes; loud CodesignError, no fallback

CI checklist

• pnpm -r typecheck — green
• pnpm lint — green (Biome, no warnings)
• pnpm -r test — 18 new + all existing tests pass

§5b checks

• Compatible: ExporterFormat enum unchanged, IPC payload unchanged, exportArtifact signature unchanged
• Upgradeable: tier-1 boundaries preserved — extractSlides is the seam where dom-to-pptx will plug in; chrome-discovery's ChromeDiscoveryDeps is the seam for tests/electron-managed Chromium later
• No bloat: 3 deps, 14.7 MB unpacked, all lazy-loaded; no stub libraries pulled in
• Elegant: no off-the-shelf "AI app" affordances; toolbar copy describes the actual output of each format

Signed-off-by: Haoqing Wang 1506751656@qq.com

[hqhq1025]

Superseded by v2 (clean cherry-pick on top of latest main). See 7-v2 PR.