Extract binder package from citation-evidence (EBIND-WP-0001)

Extracts citation-evidence/src/binder/ into this repo as the standalone
@citation-evidence/evidence-binder package: headless binding service +
in-memory link repo, active-state machine, the SharedContracts §7
rect-registry contract (registry, change pumps, hooks, SVG overlay), and
the target-neutral reference FormRenderer.

- toolchain mirrors sibling extracted repos (pnpm/tsc/vitest/eslint);
  imports rewritten from @shared/@engine aliases to the engine's
  @citation-evidence/engine package specifiers
- dependency boundary (engine + anchor only; no source/work/umbrella)
  enforced via eslint no-restricted-imports
- docs: extraction inventory + contract deltas, ADR-0001 (reference UI
  kept as supported exports), refreshed README/SCOPE/INTENT, populated
  capabilities index
- typecheck + lint green, 37 tests passing

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

src/services/bindings.ts

@@ -0,0 +1,118 @@
+/**
+ * Binding service — links EvidenceItems to structured targets.
+ *
+ * Implements `wiki/ArchitectureOverview.md` §4.6 + SharedContracts §2.4
+ * (status enum), §2.5 (relation enum). Emits §4 events:
+ * `EvidenceLinkCreated`, `EvidenceLinkUpdated`, `EvidenceItemActivated`.
+ *
+ * MVP semantics:
+ *   - `linkEvidenceToTarget` defaults `relation="supports"`, `status="candidate"`.
+ *   - `unlinkEvidence` is hard-delete; the rejected-status path is left to
+ *     a later ADR.
+ *   - `setActiveEvidence` emits an `EvidenceItemActivated` event with
+ *     `source="form-field"` so the viewer/sidebar can react.
+ */
+
+import type {
+  EvidenceLink,
+  EvidenceLinkStoredStatus,
+  EvidenceRelation,
+  EvidenceTarget,
+} from "@citation-evidence/engine/shared";
+import type { EvidenceItemId, EvidenceLinkId } from "@citation-evidence/engine/shared";
+import { newId } from "@citation-evidence/engine/shared";
+
+import type { EventBus } from "@citation-evidence/engine";
+
+import type { EvidenceLinkRepository } from "../repos/in-memory-links";
+
+export interface LinkEvidenceToTargetInput {
+  readonly evidenceItemId: EvidenceItemId;
+  readonly target: EvidenceTarget;
+  readonly relation?: EvidenceRelation;
+  readonly status?: EvidenceLinkStoredStatus;
+  readonly confidence?: number;
+  readonly createdBy?: string;
+}
+
+export interface UpdateLinkStatusInput {
+  readonly status?: EvidenceLinkStoredStatus;
+  readonly relation?: EvidenceRelation;
+  readonly confidence?: number;
+}
+
+export interface BindingService {
+  linkEvidenceToTarget(input: LinkEvidenceToTargetInput): EvidenceLink;
+  unlinkEvidence(id: EvidenceLinkId): boolean;
+  updateLink(id: EvidenceLinkId, input: UpdateLinkStatusInput): EvidenceLink;
+  getLink(id: EvidenceLinkId): EvidenceLink | null;
+  listEvidenceForTarget(target: EvidenceTarget): readonly EvidenceLink[];
+  listTargetsForEvidence(evidenceItemId: EvidenceItemId): readonly EvidenceLink[];
+  setActiveEvidence(evidenceItemId: EvidenceItemId): void;
+}
+
+export function createBindingService(
+  links: EvidenceLinkRepository,
+  bus: EventBus,
+  now: () => string = () => new Date().toISOString(),
+): BindingService {
+  return {
+    linkEvidenceToTarget(input) {
+      const ts = now();
+      const link: EvidenceLink = {
+        id: newId("evidence-link"),
+        evidenceItemId: input.evidenceItemId,
+        targetType: input.target.targetType,
+        targetId: input.target.targetId,
+        relation: input.relation ?? "supports",
+        status: input.status ?? "candidate",
+        ...(input.confidence !== undefined ? { confidence: input.confidence } : {}),
+        ...(input.createdBy !== undefined ? { createdBy: input.createdBy } : {}),
+        createdAt: ts,
+        updatedAt: ts,
+      };
+      const stored = links.create(link);
+      bus.emit({ type: "EvidenceLinkCreated", linkId: stored.id, link: stored });
+      return stored;
+    },
+    unlinkEvidence(id) {
+      const removed = links.delete(id);
+      if (removed) {
+        bus.emit({ type: "EvidenceLinkRemoved", linkId: id });
+      }
+      return removed;
+    },
+    updateLink(id, input) {
+      const existing = links.get(id);
+      if (!existing) {
+        throw new Error(`BindingService.updateLink: unknown id ${id}`);
+      }
+      const next: EvidenceLink = {
+        ...existing,
+        ...(input.status !== undefined ? { status: input.status } : {}),
+        ...(input.relation !== undefined ? { relation: input.relation } : {}),
+        ...(input.confidence !== undefined ? { confidence: input.confidence } : {}),
+        updatedAt: now(),
+      };
+      const stored = links.update(next);
+      bus.emit({ type: "EvidenceLinkUpdated", linkId: stored.id, link: stored });
+      return stored;
+    },
+    getLink(id) {
+      return links.get(id);
+    },
+    listEvidenceForTarget(target) {
+      return links.listForTarget(target);
+    },
+    listTargetsForEvidence(evidenceItemId) {
+      return links.listForEvidenceItem(evidenceItemId);
+    },
+    setActiveEvidence(evidenceItemId) {
+      bus.emit({
+        type: "EvidenceItemActivated",
+        evidenceItemId,
+        source: "form-field",
+      });
+    },
+  };
+}