Desktop runtime prune for debug metadata, Phosphor, and PDF.js

Traceability

• Spec ID: 2026-09-10-desktop-runtime-prune
• Status: Implemented
• Request: shrink the packaged Harness Studio .app by dropping pack-time debug metadata, unused Phosphor files, and unused PDF.js trees
• AI involvement: implementation and local validation by Grok 4.6

Intent

The unpacked macOS arm64 app is about 518MB. Chromium is most of that, but the staged Node runtime still ships debug metadata, the full Phosphor icon package, and both PDF.js builds. Phosphor icons are already bundled into Studio's browser assets, and the Node PDF adapter imports only the legacy PDF.js entry. Staging should keep the runtime those two facts require and drop the rest before electron-builder packs dist/app.

Acceptance Scenarios

• AC-1 Given a staged desktop node_modules tree, when staging finishes, then *.map, *.d.ts / *.d.mts / *.d.cts, and package README files are gone, while runtime JavaScript, LICENSE files, native addons, and WASM remain.
• AC-2 Given @phosphor-icons/react in the production closure, when staging finishes, then no @phosphor-icons package remains under staged node_modules. The Studio browser bundle already inlines the icons it uses.
• AC-3 Given pdfjs-dist in the production closure, when staging finishes, then the modern build/ tree, viewer web/ trees, types, webpack helper, minified copies, and source maps are gone, while legacy/build/pdf.mjs, legacy/build/pdf.worker.mjs, and the runtime support trees (cmaps, wasm, standard_fonts, iccs, image_decoders) remain. The Node adapter can still load pdfjs-dist/legacy/build/pdf.mjs.
• AC-4 Given the prune owner, when its tests run, then they assert keep and drop behaviour on a fixture tree rather than grepping packaged markup.

Non-goals

• Shrinking Electron Framework / Chromium.
• Shiki language subsetting or dropping esbuild-wasm.
• Changing Studio's PDF adapter to the modern pdfjs-dist/build entry. That build loads in Node but warns to use legacy; this change keeps the working Node path.
• Moving Phosphor to devDependencies in the npm package. Desktop staging is the pack-time owner; the Studio CLI package layout stays unchanged.
• Signing, notarization, or a smaller published npm tarball.

Plan and Tasks

1. Add packages/better-harness-desktop/scripts/prune-desktop-runtime.mjs as the keep/drop owner. Walk with node:path / readdir; do not split native paths on /.
2. Call it from scripts/stage.mjs after the production npm install.
3. Cover AC-1..AC-4 with node:test fixtures next to the existing desktop protocol tests.
4. Restage and confirm Phosphor is absent, PDF.js legacy entry still imports, and staged node_modules is smaller.

Test and Review Evidence

• npm test -w @qoder-ai/better-harness-desktop: 10 passed, including the three prune keep/drop tests (AC-1, AC-2, AC-3, AC-4).
• npm exec -w @qoder-ai/harness-studio -- vitest run test/pdf-artifact-adapter.test.ts: 4 passed against the workspace PDF.js install.
• npm run stage -w @qoder-ai/better-harness-desktop pruned 5394 files. Staged node_modules went from 285MB to 141MB. @phosphor-icons is absent. pdfjs-dist is 7.8MB and still exports getDocument from legacy/build/pdf.mjs. Zero leftover *.map, *.d.ts, or README files.