EANCH-WP-0001 T01: codify repo boundary and package shape

Finish SCOPE.md (boundary, maturity, deps, non-goals + capability blocks),
rewrite README.md as an extraction-oriented package doc with the initial
src/ module layout (selectors/pdf/highlight) and public API surface.
Selector types stay in citation-engine; selector behavior + viewer
contract owned here (ADR-0006 / SharedContracts §8).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -1,16 +1,82 @@
 # evidence-anchor
 
 Selector creation, resolution, and the `DocumentViewerAdapter` contract that
-every document viewer in the workspace implements.
+every document viewer in the citation-evidence workspace implements. This repo
+turns annotations from static marks into durable, reopenable source references.
 
-## MVP status: INTENT only
+- **Owns:** selector *behavior* — `createSelectors`, `resolveSelectors`, PDF
+  selector math, the viewer-adapter contract, and highlight/scroll helpers.
+- **Does not own:** selector *type interfaces* — those live in `citation-engine`
+  (`shared/selector`). See `ADR-0006` and `SharedContracts.md` §8.
+- **May depend on:** `citation-engine` only (DependencyMap §4). Nothing from
+  `binder/`, `source/`, or `work/` may flow back into it.
 
-During the citation-evidence MVP, code lives upstream in
-[`citation-evidence`](../citation-evidence/) under `src/anchor/`. This repo
-currently holds `INTENT.md` describing what will move here. Contract
-changes belong in
-[`citation-evidence/wiki/SharedContracts.md`](../citation-evidence/wiki/SharedContracts.md),
-not here.
+See `SCOPE.md` for the boundary and `INTENT.md` for the long-range intent.
 
-Per the dependency map, anchor depends on `shared/` and `engine/` only;
-nothing in `binder/`, `source/`, or `work/` may flow back into it.
+## Status: extracting from the umbrella
+
+The concrete anchor slice currently lives upstream in
+[`../citation-evidence/src/anchor/`](../citation-evidence/src/anchor/). Workplan
+`EANCH-WP-0001` moves it here as a standalone TypeScript package, wires the
+umbrella to consume this package, and verifies the round-trip. Shared-contract
+changes still happen in the umbrella (`citation-evidence/wiki/`), not here.
+
+## Install model
+
+Sibling-checkout, linked-package model — this repo is checked out next to its
+consumers and consumed via a local link (e.g. `link:../evidence-anchor`), not
+published to a registry during MVP. Its only shared-type dependency is
+`citation-engine`, imported through the engine's public `shared` entrypoint
+(`@citation-evidence/engine/shared`) rather than umbrella-only `@shared/*`
+aliases.
+
+## Package layout (initial extracted version)
+
+```text
+src/
+  index.ts                      public entrypoint (re-exports the surfaces below)
+  types.ts                      adapter-side types: SelectionCapture,
+                                ResolvedAnchorTarget, AnchorResolution,
+                                HighlightRenderOptions, DocumentViewerAdapter
+  selectors/
+    index.ts                    createSelectors, resolveSelectors, DEFAULT_CONTEXT_CHARS
+    create.ts                   selector creation from a captured selection
+    resolve.ts                  resolution + the exact-match confidence ladder
+    create.test.ts
+    resolve.test.ts
+  pdf/
+    pdf-selector-math.ts        page number + normalized page-rectangle math
+    pdf-selector-math.test.ts
+    pdf-viewer-adapter.tsx      concrete PDF DocumentViewerAdapter (from the spike)
+  highlight/
+    scroll-job.ts               scroll-to-target helper
+    scroll-job.test.ts
+    highlight-styles.css        highlight rendering styles
+    debug-textlayer.css         optional text-layer debugging styles
+```
+
+Boundary rules for the layout:
+
+- viewer-library imports (`pdfjs`, `react-pdf-highlighter-plus`) are confined to
+  `src/pdf/` — they never appear on `types.ts` or on the public surface;
+- `src/selectors/` is pure (no viewer/UI deps) and depends only on
+  `citation-engine` shared types;
+- the public entrypoint re-exports the stable surface consumers rely on:
+  `createSelectors`, `resolveSelectors`, the selector/resolution types, the
+  `DocumentViewerAdapter` contract, and the PDF adapter.
+
+## Public API (target surface)
+
+```ts
+import {
+  createSelectors,
+  resolveSelectors,
+  type DocumentViewerAdapter,
+  type AnchorResolution,
+} from "evidence-anchor";
+```
+
+Resolution is explicit about uncertainty — `AnchorResolution.status` is one of
+`resolved` / `ambiguous` / `unresolved` / `stale` with a `0..1` confidence, so a
+caller can highlight, ask the user to confirm, or mark a citation stale rather
+than silently highlight the wrong passage.