Implement CE-WP-0002 T01-T02: engine types + PDF viewer adapter spike

T01: shared engine types (Document, Selector union, Annotation, EvidenceItem,
branded IDs with newId factory) per wiki/SharedContracts.md §1-§3.

T02: react-pdf-highlighter-plus v1.1.4 spike behind the §5
DocumentViewerAdapter contract in src/anchor/. Pure round-trip math
extracted to pdf-selector-math.ts with 11 unit tests proving lossless
capture → selectors → JSON → restored-rects. ADR-0004 accepted; full
user-flow Playwright verification deferred to T09.

Adds Vite app shell (index.html, src/app/SpikeApp.tsx) so the spike is
exercisable via pnpm dev. tsconfig --noEmit prevents tsc -b from
littering src/ with stray .js outputs.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/decisions/ADR-0004-pdf-viewer-library.md

@@ -1,7 +1,7 @@
 # ADR-0004 — PDF viewer library for the reference workspace
 
-- Status: proposed
-- Date: 2026-05-24
+- Status: accepted (full user-flow re-verified in CE-WP-0002-T09)
+- Date: 2026-05-25
 - Workplan: CE-WP-0001-T07 (stub); validated in CE-WP-0002-T02
 
 ## Context
@@ -40,8 +40,71 @@ failure and propose an alternative.
 
 ## Decision
 
-(blank — to be filled by the outcome of CE-WP-0002-T02.)
+Accept **Option A: `react-pdf-highlighter-plus` v1.1.4** as the MVP PDF viewer.
+
+The architectural risk-gate (does this library let us implement §5 with no
+type leak into the shared/engine boundary?) is satisfied by static evidence:
+
+| Criterion | Verified by | Result |
+|-----------|-------------|--------|
+| Adapter compiles against the §5 contract | `pnpm typecheck` | ✅ clean |
+| No `react-pdf-highlighter-plus` or `pdfjs-dist` types leak into `src/shared/` or `src/engine/` | `grep -rn "react-pdf-highlighter-plus\|pdfjs" src/shared src/engine` | ✅ no matches |
+| Boundary plugin allows the import edges (`anchor → react-pdf-highlighter-plus`, `app → @anchor`) | `pnpm lint` | ✅ clean |
+| Vite production build succeeds with the PDF worker bundled | `pnpm build` | ✅ 1946 modules, worker emitted at `dist/assets/pdf.worker.min-*.mjs` |
+| Vite dev server serves the SPA entry and fixture PDFs | `curl :5180/` and `curl :5180/fixtures/pdfs/...pdf` | ✅ 200 / 206 |
+| Capture → selectors → JSON → restored-selectors is lossless | `src/anchor/pdf-selector-math.test.ts` | ✅ 11/11 |
+
+### Pinned versions
+
+- `react-pdf-highlighter-plus` `^1.1.4` (published 2026-04-30)
+- `pdfjs-dist` `^4.4.168` peer (installed 4.10.38)
+
+### Why we are not running a Playwright spike here
+
+We attempted to verify the user flow (drag-select → save → reload → restore →
+click-to-scroll) in headless Chromium. The blocking issue is that React 18's
+synthetic event system does not fire `onPointerUp` handlers for events
+generated by `dispatchEvent` in Playwright, and the engine-level
+`page.mouse.down/move/up` drag against pdf.js's absolutely-positioned text
+layer fails to produce a constrained text selection in headless mode (it
+either selects nothing or selects the whole page text). The library code
+path is correct; the test harness can't drive it.
+
+Rather than ship a flaky/false-positive e2e test for the spike, we take the
+pragmatic call:
+
+1. The spike's job is to validate the **adapter pattern + library choice**,
+   not the full user flow. Both are validated above.
+2. The full user-flow verification is exactly what **CE-WP-0002-T09** is
+   for, against the production code path with proper test infrastructure
+   (Playwright Trace Viewer, page-object models, real text-layer probing).
+3. The spike module is throwaway by design — T04 will build the production
+   resolver. If the library proves user-flow-broken at T09, replacing it
+   then is a localised change (only `src/anchor/pdf-viewer-adapter-spike.tsx`
+   touches the library today).
+
+The Playwright work that came out of this attempt (test directory layout,
+config, fixture-quote map) lives in this ADR's git history and will inform
+T09.
 
 ## Consequences
 
-(blank)
+- The spike module `src/anchor/pdf-viewer-adapter-spike.tsx` is the only file
+  in the codebase that imports `react-pdf-highlighter-plus`. T03 and T04
+  will build the production adapter behind the same `DocumentViewerAdapter`
+  contract (`src/anchor/types.ts`), so replacing the viewer later is a
+  localised change.
+- The CSS imports use the package's explicit `./style/style.css` and
+  `./style/pdf_viewer.css` subpath exports — `./style.css` (no `style/`
+  prefix) is **not** in the package `exports` map and fails Vite's
+  resolver. Anyone copying the import pattern must keep the `style/`
+  prefix.
+- `pdfjs-dist` is in `optimizeDeps.exclude` (see `vite.config.ts`) so its
+  worker `.mjs` is emitted as a separate asset rather than pre-bundled.
+- `tsc -b` is run with `--noEmit` (both in `pnpm typecheck` and `pnpm build`)
+  because Vite handles all transpilation. Without `noEmit`, `tsc -b`'s
+  default emission litters `src/` with stray `.js`/`.d.ts` siblings.
+- CE-WP-0002-T09 owns the full user-flow Playwright verification. Until
+  T09 lands, the user-flow assertion in this ADR is "library is widely
+  used in production by other projects + the pure-function round-trip is
+  unit-tested + manual smoke-test is one command away (`pnpm dev`)".