Persist capture data per session (field values, schema, links)

Capture mode state lived only in React memory and was lost when
reopening a session or remounting EngineProvider.

- Add per-session localStorage capture snapshot (schema, values, links)
- Restore on session mount; persist on field/schema/link changes
- Seed binder links from storage without spurious bus events
- Clean up capture key when session is deleted
- Integration test for reload persistence

src/app/forms/capture-persistence.test.ts

@@ -0,0 +1,95 @@
+/**
+ * CE-WP-0008 — per-session capture state round-trip.
+ */
+
+import { describe, expect, it } from "vitest";
+
+import type { SessionId } from "@shared/ids";
+
+import {
+  CAPTURE_STATE_VERSION,
+  captureStateKey,
+  defaultCaptureState,
+  loadCaptureState,
+  persistCapturePatch,
+  removeCaptureState,
+  saveCaptureState,
+} from "./capture-persistence";
+
+function memoryStorage(): Storage {
+  const map = new Map<string, string>();
+  return {
+    get length() {
+      return map.size;
+    },
+    clear: () => map.clear(),
+    getItem: (k) => map.get(k) ?? null,
+    key: (i) => [...map.keys()][i] ?? null,
+    removeItem: (k) => void map.delete(k),
+    setItem: (k, v) => void map.set(k, v),
+  };
+}
+
+const SESSION = "sess_capture" as SessionId;
+
+describe("capture-persistence", () => {
+  it("uses a per-session storage key", () => {
+    expect(captureStateKey(SESSION)).toBe(
+      "citation-evidence:session:sess_capture:capture-state:v1",
+    );
+  });
+
+  it("round-trips schema, field values, and links", () => {
+    const storage = memoryStorage();
+    const state = defaultCaptureState();
+    const withData = {
+      ...state,
+      fieldValues: { summary: "Tenant owes arrears", deadline: "2026-12-15" },
+      evidenceLinks: [
+        {
+          id: "evlink_1",
+          evidenceItemId: "evi_1",
+          targetType: "form-field",
+          targetId: "summary",
+          relation: "supports",
+          status: "candidate",
+          createdAt: "2026-06-08T00:00:00.000Z",
+          updatedAt: "2026-06-08T00:00:00.000Z",
+        },
+      ],
+    } as const;
+
+    saveCaptureState(SESSION, withData, storage);
+    const loaded = loadCaptureState(SESSION, storage);
+
+    expect(loaded?.version).toBe(CAPTURE_STATE_VERSION);
+    expect(loaded?.fieldValues).toEqual(withData.fieldValues);
+    expect(loaded?.evidenceLinks).toHaveLength(1);
+    expect(loaded?.formSchema.id).toBe("demo-form");
+  });
+
+  it("persistCapturePatch merges without dropping other fields", () => {
+    const storage = memoryStorage();
+    saveCaptureState(
+      SESSION,
+      {
+        ...defaultCaptureState(),
+        fieldValues: { amount: "1200" },
+        evidenceLinks: [],
+      },
+      storage,
+    );
+
+    persistCapturePatch(SESSION, { fieldValues: { amount: "1500", summary: "Updated" } }, storage);
+
+    const loaded = loadCaptureState(SESSION, storage);
+    expect(loaded?.fieldValues).toEqual({ amount: "1500", summary: "Updated" });
+  });
+
+  it("removeCaptureState clears the key", () => {
+    const storage = memoryStorage();
+    saveCaptureState(SESSION, defaultCaptureState(), storage);
+    removeCaptureState(SESSION, storage);
+    expect(loadCaptureState(SESSION, storage)).toBeNull();
+  });
+});