Extract engine from citation-evidence umbrella (CENG-WP-0001)

Bootstrap @citation-evidence/engine as a standalone TypeScript package
with shared types and engine services copied from the umbrella MVP.
All 89 tests pass with lint and typecheck clean.

src/shared/evidence-link.test.ts

@@ -0,0 +1,62 @@
+/**
+ * Conformance test: the runtime enum lists in `evidence-link.ts` must
+ * match the lists in `wiki/SharedContracts.md` §2.4 and §2.5 exactly.
+ *
+ * If you intentionally change an enum, update both the doc and the
+ * runtime list together — this test will tell you which one you forgot.
+ */
+
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+import { describe, expect, it } from "vitest";
+
+import {
+  EVIDENCE_LINK_STATUS_VALUES,
+  EVIDENCE_RELATION_VALUES,
+} from "./evidence-link";
+
+const HERE = fileURLToPath(new URL(".", import.meta.url));
+const CONTRACTS_PATH = resolve(HERE, "../../wiki/SharedContracts.md");
+
+function extractFencedListAfterHeading(markdown: string, heading: string): string[] {
+  const headingIndex = markdown.indexOf(heading);
+  if (headingIndex === -1) {
+    throw new Error(`Could not find heading "${heading}" in SharedContracts.md`);
+  }
+  const after = markdown.slice(headingIndex + heading.length);
+  const fenceOpen = after.indexOf("```");
+  if (fenceOpen === -1) throw new Error(`No fenced block after "${heading}"`);
+  const bodyStart = after.indexOf("\n", fenceOpen) + 1;
+  const fenceClose = after.indexOf("```", bodyStart);
+  if (fenceClose === -1) throw new Error(`Unterminated fenced block after "${heading}"`);
+  const body = after.slice(bodyStart, fenceClose);
+  return body
+    .split("\n")
+    .map((line) => line.trim())
+    .filter((line) => line.length > 0)
+    // Strip trailing "  — explanatory note" if present (none in §2.4/§2.5 today,
+    // but §2.1/§2.2 use that style — being defensive keeps the helper reusable).
+    .map((line) => line.split(/\s+[—-]\s+/)[0]!.trim());
+}
+
+describe("EvidenceLink enum conformance with SharedContracts.md", () => {
+  const markdown = readFileSync(CONTRACTS_PATH, "utf8");
+
+  it("§2.4 EvidenceLink.status matches EVIDENCE_LINK_STATUS_VALUES", () => {
+    const docValues = extractFencedListAfterHeading(
+      markdown,
+      "### 2.4 `EvidenceLink.status` (per target)",
+    );
+    expect(docValues).toEqual([...EVIDENCE_LINK_STATUS_VALUES]);
+  });
+
+  it("§2.5 EvidenceLink.relation matches EVIDENCE_RELATION_VALUES", () => {
+    const docValues = extractFencedListAfterHeading(
+      markdown,
+      "### 2.5 `EvidenceLink.relation`",
+    );
+    expect(docValues).toEqual([...EVIDENCE_RELATION_VALUES]);
+  });
+});