feat(core): add saveDomainGraph/loadDomainGraph persistence functions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

understand-anything-plugin/packages/core/src/__tests__/domain-persistence.test.ts

@@ -0,0 +1,64 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdirSync, rmSync, existsSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { saveDomainGraph, loadDomainGraph } from "../persistence/index.js";
+import type { KnowledgeGraph } from "../types.js";
+
+const testRoot = join(tmpdir(), "ua-domain-persist-test");
+
+const domainGraph: KnowledgeGraph = {
+  version: "1.0.0",
+  project: {
+    name: "test",
+    languages: ["typescript"],
+    frameworks: [],
+    description: "test",
+    analyzedAt: "2026-04-01T00:00:00.000Z",
+    gitCommitHash: "abc123",
+  },
+  nodes: [
+    {
+      id: "domain:orders",
+      type: "domain" as any,
+      name: "Orders",
+      summary: "Order management",
+      tags: [],
+      complexity: "moderate",
+    },
+  ],
+  edges: [],
+  layers: [],
+  tour: [],
+};
+
+describe("domain graph persistence", () => {
+  beforeEach(() => {
+    if (existsSync(testRoot)) rmSync(testRoot, { recursive: true });
+    mkdirSync(testRoot, { recursive: true });
+  });
+
+  afterEach(() => {
+    if (existsSync(testRoot)) rmSync(testRoot, { recursive: true });
+  });
+
+  it("saves and loads domain graph", () => {
+    saveDomainGraph(testRoot, domainGraph);
+    const loaded = loadDomainGraph(testRoot);
+    expect(loaded).not.toBeNull();
+    expect(loaded!.nodes[0].id).toBe("domain:orders");
+  });
+
+  it("returns null when no domain graph exists", () => {
+    const loaded = loadDomainGraph(testRoot);
+    expect(loaded).toBeNull();
+  });
+
+  it("saves to domain-graph.json, not knowledge-graph.json", () => {
+    saveDomainGraph(testRoot, domainGraph);
+    const domainPath = join(testRoot, ".understand-anything", "domain-graph.json");
+    const structuralPath = join(testRoot, ".understand-anything", "knowledge-graph.json");
+    expect(existsSync(domainPath)).toBe(true);
+    expect(existsSync(structuralPath)).toBe(false);
+  });
+});

understand-anything-plugin/packages/core/src/persistence/index.ts

@@ -146,3 +146,37 @@ export function loadConfig(projectRoot: string): ProjectConfig {
     return { ...DEFAULT_CONFIG };
   }
 }
+
+const DOMAIN_GRAPH_FILE = "domain-graph.json";
+
+export function saveDomainGraph(projectRoot: string, graph: KnowledgeGraph): void {
+  const dir = ensureDir(projectRoot);
+  const sanitised = sanitiseFilePaths(graph, projectRoot);
+  writeFileSync(
+    join(dir, DOMAIN_GRAPH_FILE),
+    JSON.stringify(sanitised, null, 2),
+    "utf-8",
+  );
+}
+
+export function loadDomainGraph(
+  projectRoot: string,
+  options?: { validate?: boolean },
+): KnowledgeGraph | null {
+  const filePath = join(projectRoot, UA_DIR, DOMAIN_GRAPH_FILE);
+  if (!existsSync(filePath)) return null;
+
+  const data = JSON.parse(readFileSync(filePath, "utf-8"));
+
+  if (options?.validate !== false) {
+    const result = validateGraph(data);
+    if (!result.success) {
+      throw new Error(
+        `Invalid domain graph: ${result.fatal ?? "unknown error"}`,
+      );
+    }
+    return result.data as KnowledgeGraph;
+  }
+
+  return data as KnowledgeGraph;
+}