feature: add Create Node action for orphaned node creation

Right-clicking on empty graph area (outside any node or edge) now shows
a context menu with a single 'Create Node' option. Clicking it adds a new
node with a random label and no edges, allowing the user to wire it up
manually afterwards.

- NodeContext gains isEmptyArea flag to distinguish empty-area from node
  right-clicks
- Container div contextmenu handler covers the white space below the SVG;
  SVG-level handler covers empty space within the rendered graph
- node contextmenu handler calls stopPropagation so the SVG handler never
  fires for node clicks; SVG handler also guards via target.closest check
- NodeContextMenu renders emptyAreaItems (Create Node only) vs nodeItems
  (Rename / Subgraph / Remove) based on the flag
- randomWordList extracted as a named export so NodeContextMenu can reuse
  the same word bank
- Three new Playwright e2e tests cover: empty-area menu shows only Create
  Node, created node is orphaned (no new edges), node right-click does not
  show Create Node

.gitignore

@@ -24,4 +24,6 @@ dist-ssr
 *.sw?
 
 playwright-report
-test-results
+test-results
+
+.mcp.json

e2e/app.spec.ts

@@ -10,6 +10,11 @@ function nodeByLabel(page: import('@playwright/test').Page, label: string) {
   return page.locator('g.node').filter({ hasText: label });
 }
 
+// Helper: the graph container div (empty space below the viz.js SVG)
+function graphContainer(page: import('@playwright/test').Page) {
+  return page.locator('.bg-white.rounded.shadow');
+}
+
 test.describe('ConceptSketch', () => {
   test.beforeEach(async ({ page }) => {
     await page.goto('/');
@@ -115,6 +120,42 @@ test.describe('ConceptSketch', () => {
     await expect(nodeByLabel(page, 'Start')).toBeVisible();
   });
 
+  test('right-clicking empty graph area shows only Create Node option', async ({ page }) => {
+    await graphContainer(page).click({ button: 'right', position: { x: 10, y: 400 } });
+
+    const dropdown = page.locator('.ant-dropdown:visible');
+    await expect(dropdown).toBeVisible({ timeout: 3000 });
+
+    await expect(dropdown.locator('.ant-dropdown-menu-item').filter({ hasText: 'Create Node' })).toBeVisible();
+    await expect(dropdown.locator('.ant-dropdown-menu-item').filter({ hasText: 'Rename' })).not.toBeAttached();
+    await expect(dropdown.locator('.ant-dropdown-menu-item').filter({ hasText: 'Subgraph' })).not.toBeAttached();
+    await expect(dropdown.locator('.ant-dropdown-menu-item').filter({ hasText: 'Remove' })).not.toBeAttached();
+  });
+
+  test('creates an orphaned node via Create Node in the context menu', async ({ page }) => {
+    const initialNodeCount = await page.locator('g.node').count();
+    const initialEdgeCount = await page.locator('g.edge').count();
+
+    await graphContainer(page).click({ button: 'right', position: { x: 10, y: 400 } });
+
+    await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+    await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Create Node' }).click();
+
+    await expect(page.locator('g.node')).toHaveCount(initialNodeCount + 1, { timeout: 5000 });
+    // No new edge — node is orphaned
+    await expect(page.locator('g.edge')).toHaveCount(initialEdgeCount, { timeout: 5000 });
+  });
+
+  test('right-clicking a node does not show Create Node option', async ({ page }) => {
+    await nodeByLabel(page, 'Start').click({ button: 'right' });
+
+    const dropdown = page.locator('.ant-dropdown:visible');
+    await expect(dropdown).toBeVisible({ timeout: 3000 });
+
+    await expect(dropdown.locator('.ant-dropdown-menu-item').filter({ hasText: 'Create Node' })).not.toBeAttached();
+    await expect(dropdown.locator('.ant-dropdown-menu-item').filter({ hasText: 'Rename' })).toBeVisible();
+  });
+
   test('links nodes using Ctrl+click selection', async ({ page }) => {
     // Create a third node to link to
     await nodeByLabel(page, 'Start').click();

e2e/breadcrumb.spec.ts

@@ -0,0 +1,106 @@
+import { test, expect, type Page } from '@playwright/test';
+
+async function waitForGraph(page: Page) {
+  await page.waitForSelector('svg g.node', { timeout: 15000 });
+}
+
+function nodeByLabel(page: Page, label: string) {
+  return page.locator('g.node').filter({ hasText: label });
+}
+
+async function openSubgraph(page: Page, nodeLabel: string) {
+  await nodeByLabel(page, nodeLabel).click({ button: 'right' });
+  await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+  // Wait for the dropdown animation to fully settle before clicking
+  await page.waitForTimeout(300);
+  await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Subgraph' }).click();
+  await waitForGraph(page);
+}
+
+const breadcrumbLinks = (page: Page) => page.locator('.ant-breadcrumb-link');
+
+test.describe('Breadcrumb navigation', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  test('shows "Main" as the only breadcrumb in the initial state', async ({ page }) => {
+    await expect(breadcrumbLinks(page)).toHaveCount(1);
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+  });
+
+  test('adds a breadcrumb segment when entering a subgraph', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    await expect(breadcrumbLinks(page)).toHaveCount(2);
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Start');
+  });
+
+  test('breadcrumb grows for each additional level of nesting', async ({ page }) => {
+    // Level 1: enter Start's subgraph
+    await openSubgraph(page, 'Start');
+    await expect(breadcrumbLinks(page)).toHaveCount(2);
+
+    // Level 2: enter Start's subgraph again from within level 1
+    await openSubgraph(page, 'Start');
+    await expect(breadcrumbLinks(page)).toHaveCount(3);
+  });
+
+  test('clicking the root breadcrumb from two levels deep returns to main graph', async ({ page }) => {
+    // Navigate 2 levels deep
+    await openSubgraph(page, 'Start');
+    await openSubgraph(page, 'Start');
+    await expect(breadcrumbLinks(page)).toHaveCount(3);
+
+    // Click "Main" (first item)
+    await breadcrumbLinks(page).first().click();
+
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+    await waitForGraph(page);
+    await expect(nodeByLabel(page, 'Start')).toBeVisible();
+    await expect(nodeByLabel(page, 'End')).toBeVisible();
+  });
+
+  test('clicking a middle breadcrumb navigates to that level and removes subsequent segments', async ({ page }) => {
+    // Navigate to level 1 (Start's subgraph)
+    await openSubgraph(page, 'Start');
+
+    // Add a node at level 1 so we can recognise it when we return
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Navigate to level 2
+    await openSubgraph(page, 'Start');
+    await expect(breadcrumbLinks(page)).toHaveCount(3);
+
+    // Click the level-1 breadcrumb (second item, "Start")
+    await breadcrumbLinks(page).nth(1).click();
+
+    // Breadcrumb should be truncated to 2 items
+    await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
+    // The level-1 graph still has the extra node we added
+    await waitForGraph(page);
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+  });
+
+  test('navigating forward after going back starts a fresh path from that level', async ({ page }) => {
+    // Navigate to level 1
+    await openSubgraph(page, 'Start');
+    await expect(breadcrumbLinks(page)).toHaveCount(2);
+
+    // Go back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+
+    // Navigate into End's subgraph (a different node than before)
+    await openSubgraph(page, 'End');
+
+    // Breadcrumb should be Main / End — no leftover "Start" segment
+    await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).toContainText('End');
+    await expect(page.locator('.ant-breadcrumb')).not.toContainText('Start');
+  });  
+});

e2e/load.spec.ts

@@ -0,0 +1,233 @@
+import { test, expect, type Page } from '@playwright/test';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+
+// ── fixtures ──────────────────────────────────────────────────────────────────
+
+const SIMPLE_GRAPH = {
+  id: 'main',
+  nodes: [
+    { id: 'node-a', label: 'Alpha' },
+    { id: 'node-b', label: 'Beta' },
+  ],
+  edges: [{ id: 'edge-1', from: 'node-a', to: 'node-b' }],
+};
+
+const GRAPH_WITH_SUBGRAPH = {
+  id: 'main',
+  nodes: [
+    {
+      id: 'node-a',
+      label: 'Alpha',
+      subgraph: {
+        id: 'node-a',
+        nodes: [
+          { id: 'sub-1', label: 'SubAlpha' },
+          { id: 'sub-2', label: 'SubBeta' },
+        ],
+        edges: [{ id: 'sub-edge-1', from: 'sub-1', to: 'sub-2' }],
+      },
+    },
+    { id: 'node-b', label: 'Beta' },
+  ],
+  edges: [{ id: 'edge-1', from: 'node-a', to: 'node-b' }],
+};
+
+function writeTempJson(data: object): string {
+  const name = `concept-sketch-test-${Date.now()}-${Math.random().toString(36).slice(2)}.json`;
+  const filePath = path.join(os.tmpdir(), name);
+  fs.writeFileSync(filePath, JSON.stringify(data));
+  return filePath;
+}
+
+// ── helpers ───────────────────────────────────────────────────────────────────
+
+async function waitForGraph(page: Page) {
+  await page.waitForSelector('svg g.node', { timeout: 15000 });
+}
+
+function nodeByLabel(page: Page, label: string) {
+  return page.locator('g.node').filter({ hasText: label });
+}
+
+async function openSubgraph(page: Page, nodeLabel: string) {
+  await nodeByLabel(page, nodeLabel).click({ button: 'right' });
+  await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+  await page.waitForTimeout(300);
+  await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Subgraph' }).click();
+  await waitForGraph(page);
+}
+
+function loadButton(page: Page) {
+  return page.getByTitle('Load JSON');
+}
+
+// Triggers load and waits until a specific node label appears in the graph —
+// that is the reliable signal that the full async load pipeline has finished.
+async function loadFile(page: Page, filePath: string, waitForLabel: string) {
+  const [fileChooser] = await Promise.all([
+    page.waitForEvent('filechooser'),
+    loadButton(page).click(),
+  ]);
+  await fileChooser.setFiles(filePath);
+  await expect(nodeByLabel(page, waitForLabel)).toBeVisible({ timeout: 10000 });
+}
+
+// ── tests ─────────────────────────────────────────────────────────────────────
+
+test.describe('Graph loading', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  // ── button presence ──────────────────────────────────────────────────────────
+  test('load button is visible in the header', async ({ page }) => {
+    await expect(loadButton(page)).toBeVisible();
+  });
+
+  test('clicking the load button opens a file chooser', async ({ page }) => {
+    const [fileChooser] = await Promise.all([
+      page.waitForEvent('filechooser'),
+      loadButton(page).click(),
+    ]);
+    expect(fileChooser).toBeDefined();
+  });
+
+  // ── basic load ───────────────────────────────────────────────────────────────
+  test('loaded nodes and edges replace the default graph', async ({ page }) => {
+    const filePath = writeTempJson(SIMPLE_GRAPH);
+    await loadFile(page, filePath, 'Alpha');
+
+    await expect(nodeByLabel(page, 'Alpha')).toBeVisible();
+    await expect(nodeByLabel(page, 'Beta')).toBeVisible();
+    await expect(page.locator('g.node')).toHaveCount(2);
+    await expect(page.locator('g.edge')).toHaveCount(1);
+  });
+
+  test('loading removes nodes that existed before the load', async ({ page }) => {
+    await nodeByLabel(page, 'Start').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    const filePath = writeTempJson(SIMPLE_GRAPH);
+    await loadFile(page, filePath, 'Alpha');
+
+    await expect(page.locator('g.node')).toHaveCount(2, { timeout: 5000 });
+    await expect(nodeByLabel(page, 'Start')).not.toBeAttached();
+    await expect(nodeByLabel(page, 'End')).not.toBeAttached();
+  });
+
+  test('a second load completely replaces the previously loaded graph', async ({ page }) => {
+    const firstFile = writeTempJson(SIMPLE_GRAPH);
+    await loadFile(page, firstFile, 'Alpha');
+
+    const secondFile = writeTempJson({
+      id: 'main',
+      nodes: [
+        { id: 'n1', label: 'Gamma' },
+        { id: 'n2', label: 'Delta' },
+      ],
+      edges: [{ id: 'e1', from: 'n1', to: 'n2' }],
+    });
+    await loadFile(page, secondFile, 'Gamma');
+
+    await expect(nodeByLabel(page, 'Gamma')).toBeVisible();
+    await expect(nodeByLabel(page, 'Delta')).toBeVisible();
+    await expect(nodeByLabel(page, 'Alpha')).not.toBeAttached();
+    await expect(page.locator('g.node')).toHaveCount(2);
+  });
+
+  // ── navigation reset ──────────────────────────────────────────────────────────
+  test('loading resets the breadcrumb to "Main" only', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await expect(page.locator('.ant-breadcrumb-link')).toHaveCount(2);
+
+    const filePath = writeTempJson(SIMPLE_GRAPH);
+    await loadFile(page, filePath, 'Alpha');
+
+    await expect(page.locator('.ant-breadcrumb-link')).toHaveCount(1, { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+    await expect(page.locator('.ant-breadcrumb')).not.toContainText('Start');
+  });
+
+  test('loading while inside a subgraph shows the loaded main graph', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    const filePath = writeTempJson(SIMPLE_GRAPH);
+    await loadFile(page, filePath, 'Alpha');
+
+    await expect(nodeByLabel(page, 'Alpha')).toBeVisible();
+    await expect(nodeByLabel(page, 'Beta')).toBeVisible();
+    await expect(nodeByLabel(page, 'Start')).not.toBeAttached();
+    await expect(nodeByLabel(page, 'End')).not.toBeAttached();
+  });
+
+  // ── subgraph restoration ──────────────────────────────────────────────────────
+  test('subgraph from loaded JSON is accessible via the context menu', async ({ page }) => {
+    const filePath = writeTempJson(GRAPH_WITH_SUBGRAPH);
+    await loadFile(page, filePath, 'Alpha');
+
+    await openSubgraph(page, 'Alpha');
+
+    await expect(nodeByLabel(page, 'SubAlpha')).toBeVisible();
+    await expect(nodeByLabel(page, 'SubBeta')).toBeVisible();
+    await expect(page.locator('g.node')).toHaveCount(2);
+    await expect(page.locator('g.edge')).toHaveCount(1);
+  });
+
+  test('breadcrumb shows the loaded node label when navigated into its subgraph', async ({ page }) => {
+    const filePath = writeTempJson(GRAPH_WITH_SUBGRAPH);
+    await loadFile(page, filePath, 'Alpha');
+    await openSubgraph(page, 'Alpha');
+
+    await expect(page.locator('.ant-breadcrumb-link')).toHaveCount(2);
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Alpha');
+  });
+
+  test('navigating back from a loaded subgraph restores the loaded main graph', async ({ page }) => {
+    const filePath = writeTempJson(GRAPH_WITH_SUBGRAPH);
+    await loadFile(page, filePath, 'Alpha');
+    await openSubgraph(page, 'Alpha');
+
+    await page.locator('.ant-breadcrumb-link').first().click();
+    await waitForGraph(page);
+
+    await expect(nodeByLabel(page, 'Alpha')).toBeVisible();
+    await expect(nodeByLabel(page, 'Beta')).toBeVisible();
+    await expect(page.locator('g.node')).toHaveCount(2);
+  });
+
+  test('node without a subgraph in the loaded JSON does not expose a pre-existing subgraph', async ({ page }) => {
+    // First load graph with subgraph, then load a graph without
+    const withSubgraph = writeTempJson(GRAPH_WITH_SUBGRAPH);
+    await loadFile(page, withSubgraph, 'Alpha');
+    await openSubgraph(page, 'Alpha');
+    await expect(nodeByLabel(page, 'SubAlpha')).toBeVisible();
+
+    // Go back and load a plain graph
+    await page.locator('.ant-breadcrumb-link').first().click();
+    await waitForGraph(page);
+    const plain = writeTempJson(SIMPLE_GRAPH);
+    await loadFile(page, plain, 'Alpha');
+
+    // Alpha no longer has a subgraph — entering it should create a fresh default graph
+    await openSubgraph(page, 'Alpha');
+    await expect(nodeByLabel(page, 'Start')).toBeVisible();
+    await expect(nodeByLabel(page, 'End')).toBeVisible();
+    await expect(nodeByLabel(page, 'SubAlpha')).not.toBeAttached();
+  });
+
+  // ── sidebar tree ──────────────────────────────────────────────────────────────
+  test('sidebar tree reflects subgraph structure from loaded JSON', async ({ page }) => {
+    const filePath = writeTempJson(GRAPH_WITH_SUBGRAPH);
+    await loadFile(page, filePath, 'Alpha');
+
+    // Expand sidebar
+    await page.locator('header button').first().click();
+    await expect(page.locator('.ant-layout-sider')).not.toHaveClass(/ant-layout-sider-collapsed/, { timeout: 3000 });
+
+    // Alpha has a subgraph so it appears in the tree
+    await expect(page.locator('.ant-tree-title').filter({ hasText: 'Alpha' })).toBeVisible({ timeout: 3000 });
+  });
+});

e2e/save.spec.ts

@@ -0,0 +1,195 @@
+import { test, expect, type Page, type Download } from '@playwright/test';
+import * as fs from 'fs';
+
+// ── types mirroring saveGraph.ts ──────────────────────────────────────────────
+interface SavedEdge { id: string; from: string; to: string; }
+interface SavedNode { id: string; label?: string; subgraph?: SavedGraph; }
+interface SavedGraph { id: string; nodes: SavedNode[]; edges: SavedEdge[]; }
+
+// ── helpers ───────────────────────────────────────────────────────────────────
+async function waitForGraph(page: Page) {
+  await page.waitForSelector('svg g.node', { timeout: 15000 });
+}
+
+function nodeByLabel(page: Page, label: string) {
+  return page.locator('g.node').filter({ hasText: label });
+}
+
+async function openSubgraph(page: Page, nodeLabel: string) {
+  await nodeByLabel(page, nodeLabel).click({ button: 'right' });
+  await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+  await page.waitForTimeout(300);
+  await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Subgraph' }).click();
+  await waitForGraph(page);
+}
+
+function saveButton(page: Page) {
+  return page.getByTitle('Save as JSON');
+}
+
+async function triggerSave(page: Page): Promise<Download> {
+  const [download] = await Promise.all([
+    page.waitForEvent('download'),
+    saveButton(page).click(),
+  ]);
+  return download;
+}
+
+async function getSavedJson(page: Page): Promise<SavedGraph> {
+  const download = await triggerSave(page);
+  const filePath = await download.path();
+  expect(filePath).not.toBeNull();
+  return JSON.parse(fs.readFileSync(filePath!, 'utf-8')) as SavedGraph;
+}
+
+// ── tests ─────────────────────────────────────────────────────────────────────
+test.describe('Graph saving', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  // ── button presence ─────────────────────────────────────────────────────────
+  test('save button is visible in the header', async ({ page }) => {
+    await expect(saveButton(page)).toBeVisible();
+  });
+
+  // ── download mechanics ──────────────────────────────────────────────────────
+  test('clicking save downloads a file named concept-sketch.json', async ({ page }) => {
+    const download = await triggerSave(page);
+    expect(download.suggestedFilename()).toBe('concept-sketch.json');
+  });
+
+  test('downloaded file is valid JSON', async ({ page }) => {
+    const download = await triggerSave(page);
+    const filePath = await download.path();
+    expect(filePath).not.toBeNull();
+    expect(() => JSON.parse(fs.readFileSync(filePath!, 'utf-8'))).not.toThrow();
+  });
+
+  // ── root graph structure ────────────────────────────────────────────────────
+  test('saved JSON has id, nodes and edges at the root', async ({ page }) => {
+    const data = await getSavedJson(page);
+    expect(data.id).toBe('main');
+    expect(Array.isArray(data.nodes)).toBe(true);
+    expect(Array.isArray(data.edges)).toBe(true);
+  });
+
+  test('default graph saves Start and End nodes with one connecting edge', async ({ page }) => {
+    const data = await getSavedJson(page);
+    expect(data.nodes).toHaveLength(2);
+    const labels = data.nodes.map(n => n.label);
+    expect(labels).toContain('Start');
+    expect(labels).toContain('End');
+    expect(data.edges).toHaveLength(1);
+  });
+
+  test('edge from/to ids reference nodes that exist in the graph', async ({ page }) => {
+    const data = await getSavedJson(page);
+    const nodeIds = new Set(data.nodes.map(n => n.id));
+    for (const edge of data.edges) {
+      expect(nodeIds.has(edge.from)).toBe(true);
+      expect(nodeIds.has(edge.to)).toBe(true);
+    }
+  });
+
+  // ── edits reflected in the save ─────────────────────────────────────────────
+  test('newly added node appears in the saved JSON', async ({ page }) => {
+    await nodeByLabel(page, 'Start').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    const data = await getSavedJson(page);
+    expect(data.nodes).toHaveLength(3);
+    expect(data.edges).toHaveLength(2);
+  });
+
+  test('renamed node label appears correctly in the saved JSON', async ({ page }) => {
+    await nodeByLabel(page, 'Start').click({ button: 'right' });
+    await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+    await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Rename' }).click();
+
+    const modal = page.locator('.ant-modal');
+    await expect(modal).toBeVisible({ timeout: 3000 });
+    await modal.locator('.ant-input').clear();
+    await modal.locator('.ant-input').fill('Concept');
+    await modal.locator('.ant-btn-primary').click();
+    await expect(modal).not.toBeVisible();
+    await expect(nodeByLabel(page, 'Concept')).toBeVisible({ timeout: 5000 });
+
+    const data = await getSavedJson(page);
+    const labels = data.nodes.map(n => n.label);
+    expect(labels).toContain('Concept');
+    expect(labels).not.toContain('Start');
+  });
+
+  test('removed node is absent from the saved JSON', async ({ page }) => {
+    await nodeByLabel(page, 'End').click({ button: 'right' });
+    await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+    await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Remove' }).click();
+    await expect(page.locator('g.node')).toHaveCount(1, { timeout: 5000 });
+
+    const data = await getSavedJson(page);
+    expect(data.nodes).toHaveLength(1);
+    expect(data.nodes.map(n => n.label)).not.toContain('End');
+  });
+
+  // ── subgraph serialisation ──────────────────────────────────────────────────
+  test('entering a subgraph and returning adds it nested inside the parent node', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await page.locator('.ant-breadcrumb-link').first().click();
+    await waitForGraph(page);
+
+    const data = await getSavedJson(page);
+    const startNode = data.nodes.find(n => n.label === 'Start')!;
+    expect(startNode.subgraph).toBeDefined();
+    expect(startNode.subgraph!.nodes).toHaveLength(2);
+    expect(startNode.subgraph!.edges).toHaveLength(1);
+  });
+
+  test('subgraph id matches the id of the node that contains it', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await page.locator('.ant-breadcrumb-link').first().click();
+    await waitForGraph(page);
+
+    const data = await getSavedJson(page);
+    const startNode = data.nodes.find(n => n.label === 'Start')!;
+    expect(startNode.subgraph!.id).toBe(startNode.id);
+  });
+
+  test('node without a subgraph has no subgraph key in the JSON', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await page.locator('.ant-breadcrumb-link').first().click();
+    await waitForGraph(page);
+
+    const data = await getSavedJson(page);
+    const endNode = data.nodes.find(n => n.label === 'End')!;
+    expect(endNode.subgraph).toBeUndefined();
+  });
+
+  test('nodes added inside a subgraph are serialised in the nested subgraph', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    // Add one extra node inside the subgraph
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    await page.locator('.ant-breadcrumb-link').first().click();
+    await waitForGraph(page);
+
+    const data = await getSavedJson(page);
+    const startNode = data.nodes.find(n => n.label === 'Start')!;
+    expect(startNode.subgraph!.nodes).toHaveLength(3);
+    expect(startNode.subgraph!.edges).toHaveLength(2);
+  });
+
+  test('saving from inside a subgraph includes the full hierarchy from root', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    // Still inside the subgraph when saving
+    const data = await getSavedJson(page);
+    // Root must still be present
+    expect(data.id).toBe('main');
+    expect(data.nodes.map(n => n.label)).toContain('Start');
+    // And the subgraph must be nested
+    const startNode = data.nodes.find(n => n.label === 'Start')!;
+    expect(startNode.subgraph).toBeDefined();
+  });
+});

e2e/subgraph-preservation.spec.ts

@@ -0,0 +1,142 @@
+import { test, expect, type Page } from '@playwright/test';
+
+async function waitForGraph(page: Page) {
+  await page.waitForSelector('svg g.node', { timeout: 15000 });
+}
+
+function nodeByLabel(page: Page, label: string) {
+  return page.locator('g.node').filter({ hasText: label });
+}
+
+async function openSubgraph(page: Page, nodeLabel: string) {
+  await nodeByLabel(page, nodeLabel).click({ button: 'right' });
+  await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+  await page.waitForTimeout(300);
+  await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Subgraph' }).click();
+  await waitForGraph(page);
+}
+
+const breadcrumbLinks = (page: Page) => page.locator('.ant-breadcrumb-link');
+
+test.describe('Subgraph preservation during breadcrumb navigation', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  test('nodes added to a subgraph are preserved after navigating to root and back', async ({ page }) => {
+    // Enter Start's subgraph and add a node
+    await openSubgraph(page, 'Start');
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Go back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Re-enter the same subgraph
+    await openSubgraph(page, 'Start');
+
+    // The extra node should still be there
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+  });
+
+  test('main graph is preserved when navigating into a subgraph and back', async ({ page }) => {
+    // Add a node to the main graph
+    await nodeByLabel(page, 'Start').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Navigate into End's subgraph
+    await openSubgraph(page, 'End');
+
+    // Go back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Main graph should still have 3 nodes
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+    await expect(nodeByLabel(page, 'Start')).toBeVisible();
+    await expect(nodeByLabel(page, 'End')).toBeVisible();
+  });
+
+  test('two sibling subgraphs preserve their states independently', async ({ page }) => {
+    // Enter Start's subgraph and add 1 extra node (3 total)
+    await openSubgraph(page, 'Start');
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Enter End's subgraph and add 2 extra nodes (4 total)
+    await openSubgraph(page, 'End');
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(4, { timeout: 5000 });
+
+    // Back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Re-enter Start's subgraph — should still have 3 nodes
+    await openSubgraph(page, 'Start');
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Back to main
+    await breadcrumbLinks(page).first().click();
+    await waitForGraph(page);
+
+    // Re-enter End's subgraph — should still have 4 nodes
+    await openSubgraph(page, 'End');
+    await expect(page.locator('g.node')).toHaveCount(4, { timeout: 5000 });
+  });
+
+  test('intermediate level subgraph is preserved when navigating back from deeper nesting', async ({ page }) => {
+    // Enter Start's subgraph (level 1) and add a node
+    await openSubgraph(page, 'Start');
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Go one level deeper (level 2)
+    await openSubgraph(page, 'Start');
+    await expect(breadcrumbLinks(page)).toHaveCount(3, { timeout: 3000 });
+
+    // Navigate all the way back to root
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Re-enter Start's subgraph (level 1) — the 3-node state must be intact
+    await openSubgraph(page, 'Start');
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+  });
+
+  test('edges added inside a subgraph are preserved after navigating away and back', async ({ page }) => {
+    // Enter Start's subgraph, create a node by clicking End, then link them
+    await openSubgraph(page, 'Start');
+    const edgeCountBefore = await page.locator('g.edge').count();
+
+    // Ctrl+click Start to select it as a parent for linking
+    await page.keyboard.down('Control');
+    await nodeByLabel(page, 'Start').click();
+    await page.keyboard.up('Control');
+    // Click End without Ctrl to link selected Start → End
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.edge')).toHaveCount(edgeCountBefore + 1, { timeout: 5000 });
+
+    // Navigate back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Re-enter the subgraph — extra edge must still be there
+    await openSubgraph(page, 'Start');
+    await expect(page.locator('g.edge')).toHaveCount(edgeCountBefore + 1, { timeout: 5000 });
+  });
+});

e2e/tree-navigation.spec.ts

@@ -0,0 +1,248 @@
+import { test, expect, type Page } from '@playwright/test';
+
+async function waitForGraph(page: Page) {
+  await page.waitForSelector('svg g.node', { timeout: 15000 });
+}
+
+function nodeByLabel(page: Page, label: string) {
+  return page.locator('g.node').filter({ hasText: label });
+}
+
+async function openSidebar(page: Page) {
+  const sider = page.locator('.ant-layout-sider');
+  const isCollapsed = await sider.evaluate(el => el.classList.contains('ant-layout-sider-collapsed'));
+  if (isCollapsed) {
+    await page.locator('header button').first().click();
+    await expect(sider).not.toHaveClass(/ant-layout-sider-collapsed/, { timeout: 3000 });
+  }
+}
+
+async function openSubgraph(page: Page, nodeLabel: string) {
+  await nodeByLabel(page, nodeLabel).click({ button: 'right' });
+  await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+  await page.waitForTimeout(300);
+  await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Subgraph' }).click();
+  await waitForGraph(page);
+}
+
+function treeNodeByLabel(page: Page, label: string) {
+  return page.locator('.ant-tree-node-content-wrapper').filter({ hasText: label });
+}
+
+const breadcrumbLinks = (page: Page) => page.locator('.ant-breadcrumb-link');
+
+test.describe('Tree navigation', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  test('sidebar tree is empty before any subgraphs are created', async ({ page }) => {
+    await openSidebar(page);
+    await expect(page.locator('.ant-tree-title')).toHaveCount(0);
+  });
+
+  test('creating a subgraph adds its node to the sidebar tree', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    await openSidebar(page);
+    await expect(treeNodeByLabel(page, 'Start')).toBeVisible({ timeout: 3000 });
+  });
+
+  test('clicking a tree node navigates to its subgraph', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    // Go back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Navigate via tree
+    await openSidebar(page);
+    await treeNodeByLabel(page, 'Start').click();
+
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Start', { timeout: 3000 });
+    await waitForGraph(page);
+    await expect(nodeByLabel(page, 'Start')).toBeVisible();
+    await expect(nodeByLabel(page, 'End')).toBeVisible();
+  });
+
+  test('clicking a tree node updates the breadcrumb to show the full path', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    // Go back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+
+    await openSidebar(page);
+    await treeNodeByLabel(page, 'Start').click();
+
+    await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Start');
+  });
+
+  test('clicking a nested tree node navigates directly with the full breadcrumb path', async ({ page }) => {
+    // Create level 1: Start → Start's subgraph
+    await openSubgraph(page, 'Start');
+    // Create level 2: Start → Start's sub-subgraph
+    await openSubgraph(page, 'Start');
+
+    // Go back all the way to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Navigate to level 2 directly via tree
+    await openSidebar(page);
+    // Expand the root Start node to reveal its child
+    await page.locator('.ant-tree-switcher').first().click();
+    const treeNodes = page.locator('.ant-tree-node-content-wrapper').filter({ hasText: 'Start' });
+    // The deepest node is the last one in the tree
+    await treeNodes.last().click();
+
+    // Breadcrumb should show 3 levels: Main / Start / Start
+    await expect(breadcrumbLinks(page)).toHaveCount(3, { timeout: 3000 });
+    await waitForGraph(page);
+  });
+
+  test('tree navigation from inside one subgraph jumps directly to another', async ({ page }) => {
+    // Create subgraph for Start
+    await openSubgraph(page, 'Start');
+    // Go back, create subgraph for End
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await openSubgraph(page, 'End');
+
+    // Now we are inside End's subgraph — navigate to Start's subgraph via tree
+    await openSidebar(page);
+    await treeNodeByLabel(page, 'Start').click();
+
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Start', { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).not.toContainText('End');
+    await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
+    await waitForGraph(page);
+  });
+
+  test('subgraph content is preserved when navigating away and back via tree', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    // Add a node in Start's subgraph
+    await nodeByLabel(page, 'End').click();
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+
+    // Go back to main
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    // Navigate back via tree
+    await openSidebar(page);
+    await treeNodeByLabel(page, 'Start').click();
+
+    await waitForGraph(page);
+    await expect(page.locator('g.node')).toHaveCount(3, { timeout: 5000 });
+  });
+});
+
+test.describe('Tree highlighting', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  test('tree node is highlighted when entering its subgraph via context menu', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+
+    await openSidebar(page);
+    await expect(treeNodeByLabel(page, 'Start')).toHaveClass(/ant-tree-node-selected/, { timeout: 3000 });
+  });
+
+  test('tree node is highlighted when navigating to it via tree click', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+
+    await openSidebar(page);
+    await treeNodeByLabel(page, 'Start').click();
+
+    await expect(treeNodeByLabel(page, 'Start')).toHaveClass(/ant-tree-node-selected/, { timeout: 3000 });
+  });
+
+  test('tree node is deselected when navigating back to main via breadcrumb', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await openSidebar(page);
+    await expect(treeNodeByLabel(page, 'Start')).toHaveClass(/ant-tree-node-selected/, { timeout: 3000 });
+
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+
+    await expect(treeNodeByLabel(page, 'Start')).not.toHaveClass(/ant-tree-node-selected/, { timeout: 3000 });
+  });
+
+  test('highlight switches between tree nodes when navigating between sibling subgraphs', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await openSubgraph(page, 'End');
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    await openSidebar(page);
+
+    // Navigate to Start's subgraph via tree
+    await treeNodeByLabel(page, 'Start').click();
+    await expect(treeNodeByLabel(page, 'Start')).toHaveClass(/ant-tree-node-selected/, { timeout: 3000 });
+    await expect(treeNodeByLabel(page, 'End')).not.toHaveClass(/ant-tree-node-selected/);
+
+    // Navigate to End's subgraph via tree
+    await treeNodeByLabel(page, 'End').click();
+    await expect(treeNodeByLabel(page, 'End')).toHaveClass(/ant-tree-node-selected/, { timeout: 3000 });
+    await expect(treeNodeByLabel(page, 'Start')).not.toHaveClass(/ant-tree-node-selected/);
+  });
+});
+
+test.describe('Tree node removal', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  test('removing a node with a subgraph removes it from the tree', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    await openSidebar(page);
+    await expect(treeNodeByLabel(page, 'Start')).toBeVisible();
+
+    await nodeByLabel(page, 'Start').click({ button: 'right' });
+    await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+    await page.waitForTimeout(300);
+    await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Remove' }).click();
+
+    await expect(treeNodeByLabel(page, 'Start')).not.toBeAttached({ timeout: 3000 });
+  });
+
+  test('removing a node without a subgraph does not affect the tree', async ({ page }) => {
+    await openSubgraph(page, 'Start');
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await waitForGraph(page);
+
+    await openSidebar(page);
+    await expect(page.locator('.ant-tree-title')).toHaveCount(1);
+
+    // Remove End (no subgraph)
+    await nodeByLabel(page, 'End').click({ button: 'right' });
+    await expect(page.locator('.ant-dropdown:visible')).toBeVisible({ timeout: 3000 });
+    await page.waitForTimeout(300);
+    await page.locator('.ant-dropdown-menu-item').filter({ hasText: 'Remove' }).click();
+
+    // Tree still has exactly one node (Start)
+    await expect(page.locator('.ant-tree-title')).toHaveCount(1);
+    await expect(treeNodeByLabel(page, 'Start')).toBeVisible();
+  });
+});

src/App.tsx

@@ -1,12 +1,16 @@
-import React, { useEffect, useEffectEvent, useState } from 'react';
+import React, { useEffectEvent, useRef, useState } from 'react';
 import { Layout, theme, Breadcrumb, Button, Space, Tree } from 'antd';
-import Graph from './components/Graph';
+import Graph, { type GraphHandle } from './components/Graph';
 import type { BreadcrumbItemType } from 'antd/es/breadcrumb/Breadcrumb';
 import { useKeysdownStore } from './stores/ArrayStore';
 import {
   MenuFoldOutlined,
-  MenuUnfoldOutlined
+  MenuUnfoldOutlined,
+  SaveOutlined,
+  FolderOpenOutlined,
 } from '@ant-design/icons';
+import { saveConceptSketch } from './utils/saveGraph';
+import { loadConceptSketch } from './utils/loadGraph';
 import { useGraphLayersTreeStore } from './stores/TreeStore';
 
 const { Header, Content, Sider } = Layout;
@@ -32,10 +36,21 @@ const App: React.FC = () => {
     onKeyUp(ev.key);
   });
   const treeData = useGraphLayersTreeStore(store => store.tree);
+  const nodesFlatById = useGraphLayersTreeStore(store => store.nodesFlatById);
+  const parentIdByChildId = useGraphLayersTreeStore(store => store.parentIdByChildId);
+  const graphRef = useRef<GraphHandle>(null);
+  const [activeGraphId, setActiveGraphId] = useState('main');
 
-  useEffect(() => {
-    console.info(treeData);
-  }, [treeData])
+  function buildPathToNode(nodeId: string) {
+    const path: Array<{ id: string; name: string | undefined }> = [];
+    let current: string | undefined = nodeId;
+    while (current && nodesFlatById.has(current)) {
+      const node = nodesFlatById.get(current)!;
+      path.unshift({ id: current, name: node.title as string | undefined });
+      current = parentIdByChildId.get(current);
+    }
+    return [{ id: 'main', name: 'Main' }, ...path];
+  }
 
   return (
     <Layout>
@@ -47,13 +62,19 @@ const App: React.FC = () => {
           checkable
           treeData={treeData}
           defaultExpandAll={true}
+          selectedKeys={[activeGraphId]}
           style={{
             borderRadius: 0
           }}
+          onSelect={(keys) => {
+            const nodeId = keys[0] as string;
+            if (!nodeId) return;
+            graphRef.current?.navigateTo(nodeId, buildPathToNode(nodeId));
+          }}
         />
       </Sider>
       <Layout>
-        <Header style={{ padding: 0, background: colorBgContainer }}>
+        <Header style={{ padding: 0, background: colorBgContainer, display: 'flex', alignItems: 'center', justifyContent: 'space-between' }}>
           <Space>
             <div style={{ background: '#001529' }}>
               <Button
@@ -70,6 +91,32 @@ const App: React.FC = () => {
             </div>
             <Breadcrumb items={graphLevel} />
           </Space>
+          <div style={{ background: '#001529', display: 'flex' }}>
+            <Button
+              type="text"
+              icon={<FolderOpenOutlined />}
+              onClick={loadConceptSketch}
+              title="Load JSON"
+              style={{
+                fontSize: '16px',
+                width: 32,
+                height: 32,
+                color: colorBgContainer,
+              }}
+            />
+            <Button
+              type="text"
+              icon={<SaveOutlined />}
+              onClick={saveConceptSketch}
+              title="Save as JSON"
+              style={{
+                fontSize: '16px',
+                width: 32,
+                height: 32,
+                color: colorBgContainer,
+              }}
+            />
+          </div>
         </Header>
         <Content
           style={{
@@ -80,7 +127,7 @@ const App: React.FC = () => {
             borderRadius: '6px'
           }}
         >
-          <Graph setGraphPath={setGraphLevel} />
+          <Graph ref={graphRef} setGraphPath={setGraphLevel} onNavigate={setActiveGraphId} />
         </Content>
       </Layout>
     </Layout>

src/components/Graph.tsx

@@ -1,4 +1,4 @@
-import { createContext, useEffect, useRef, useState } from "react";
+import { createContext, forwardRef, useEffect, useImperativeHandle, useRef, useState } from "react";
 import Viz from 'viz.js';
 import { Module, render } from 'viz.js/full.render.js';
 import * as d3 from 'd3';
@@ -8,6 +8,7 @@ import NodeContextMenu from "./NodeContextMenu";
 import NodeRenameModal from "./NodeRenameModal";
 import { useGraphsStore } from "../stores/GraphsStore";
 import { useKeysdownStore, useSelectedNodesStore } from "../stores/ArrayStore";
+import { useLoadStore } from "../stores/LoadStore";
 
 
 export class GraphModel {
@@ -45,6 +46,7 @@ export interface NodeContext {
   nodeId: string;
   nodeName?: string;
   coords: { x: number, y: number };
+  isEmptyArea?: boolean;
 }
 
 export interface GraphContext {
@@ -62,14 +64,21 @@ export interface OpenNodeContext {
 const viz = new Viz({ Module, render });
 export const graphContext = createContext<GraphContext | null>(null);
 
-export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<React.SetStateAction<BreadcrumbItemType[]>> }) {
+export interface GraphHandle {
+  navigateTo: (nodeId: string, path: Array<{ id: string; name: string | undefined }>) => void;
+}
+
+const Graph = forwardRef<GraphHandle, { setGraphPath: React.Dispatch<React.SetStateAction<BreadcrumbItemType[]>>, onNavigate?: (graphId: string) => void }>(function Graph({ setGraphPath, onNavigate }, ref) {
   const containerRef = useRef(null);
   const [graph, setGraph] = useState(defaultGraph());
   const [contextMenuOpened, openContextMenu] = useState(false);
   const [renameModalOpened, openRenameModal] = useState(false);
   const [graphId, selectGraphId] = useState('main');
+  const graphIdRef = useRef(graphId);
   const [graphsPath, setGraphsPath] = useState([createPathSegment('main', 'Main')])
-  const [nodeContext, openNodeContext] = useState<null | NodeContext>(null);
+  const [nodeContext, openNodeContext] = useState<null | NodeContext>(null);  
+  graphIdRef.current = graphId;
+
   const graphContextValue = {
     graphId: graphId,
     selectGraphId: selectGraphId,
@@ -82,6 +91,7 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
   const isNodeSelected = useSelectedNodesStore(store => store.has);
   const anyNodeSelected = useSelectedNodesStore(store => store.hasAny);
   const deselectAllNodes = useSelectedNodesStore(store => store.clear);
+  const loadCount = useLoadStore(state => state.loadCount);
 
   useEffect(() => {
     setGraphPath(graphsPath);
@@ -92,12 +102,50 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [graph]);
 
+  // Persist graph edits to the store so they survive breadcrumb navigation.
+  // We intentionally read graphId via ref (not as a dep) so this effect only
+  // fires on graph content changes, never on navigation (graphId changes).
+  useEffect(() => {
+    const state = useGraphsStore.getState() as { graphsById: Map<string, GraphModel> };
+    state.graphsById.set(graphIdRef.current, graph);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [graph]);
+
   useEffect(() => {
     if (nodeContext) {
       openContextMenu(true);
     }
   }, [nodeContext]);
 
+  useEffect(() => {
+    const container = containerRef.current as unknown as HTMLElement;
+    if (!container) return;
+    const handler = (event: MouseEvent) => {
+      if ((event.target as Element).closest('svg')) return;
+      event.preventDefault();
+      openNodeContext({
+        nodeId: '',
+        coords: { x: event.clientX, y: event.clientY },
+        isEmptyArea: true,
+      });
+    };
+    container.addEventListener('contextmenu', handler);
+    return () => container.removeEventListener('contextmenu', handler);
+  }, []);
+
+  useEffect(() => {
+    if (loadCount === 0) return;
+    const state = useGraphsStore.getState() as { graphsById: Map<string, GraphModel> };
+    const mainGraph = state.graphsById.get('main');
+    if (mainGraph) setGraph(mainGraph);
+    selectGraphId('main');
+    setGraphsPath([createPathSegment('main', 'Main')]);
+    openNodeContext(null);
+    openContextMenu(false);
+    onNavigate?.('main');
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [loadCount]);
+
   useEffect(() => {
     if (nodeContext?.nodeId === graphId) {
       graphsPath.push(createPathSegment(nodeContext.nodeId, nodeContext.nodeName));
@@ -109,6 +157,7 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
     if (graph) {
       setGraph(graph);
     }
+    onNavigate?.(graphId);
   }, [graphId]);
 
   async function renderGraph() {
@@ -171,12 +220,26 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
         }
 
         event.preventDefault();
+        event.stopPropagation();
         openNodeContext({
           nodeId: id,
           nodeName: node.label,
           coords: { x: event.clientX, y: event.clientY },
         })
       });
+
+    svg.on('contextmenu', function (event) {
+      const target = event.target as Element;
+      if (target.closest('g.node') || target.closest('g.edge')) {
+        return;
+      }
+      event.preventDefault();
+      openNodeContext({
+        nodeId: '',
+        coords: { x: event.clientX, y: event.clientY },
+        isEmptyArea: true,
+      });
+    });
   }
 
   function linkSelectedNodesAsParents(childNodeId: string) {
@@ -190,11 +253,7 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
   }
 
   function getRandomWords(count: number) {
-    const wordList = ['Apple', 'Sun', 'Flame', 'Earth', 'Forest', 'Dream', 'Sky', 'Shadow', 'Flower', 'Ocean', 'River', 'Path', 'Sand', 'Night', 'Star', 'Rain', 'Light', 'Tree', 'Wave', 'Storm', 'Stone', 'Snow', 'Cloud', 'Heart', 'Mountain', 'Leaf', 'Bird', 'Wind', 'Fire', 'Wolf'];
-
-    return wordList
-      .sort(() => Math.random() - 0.5)
-      .slice(0, count);
+    return randomWordList(count);
   }
 
   function createPathSegment(
@@ -216,6 +275,15 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
     } as BreadcrumbItemType;
   }
 
+  useImperativeHandle(ref, () => ({
+    navigateTo(nodeId, path) {
+      const newPath = path.map(p => createPathSegment(p.id, p.name));
+      openNodeContext(null);
+      setGraphsPath(newPath);
+      selectGraphId(nodeId);
+    }
+  }));
+
   return (
     <div className="flex-1 p-4">
       <div ref={containerRef} className="w-full h-full bg-white rounded shadow" style={{ minHeight: '600px', overflow: 'auto' }}>
@@ -236,6 +304,13 @@ export default function Graph({ setGraphPath }: { setGraphPath: React.Dispatch<R
       </graphContext.Provider>
     </div>
   )
+});
+
+export default Graph;
+
+export function randomWordList(count: number) {
+  const wordList = ['Apple', 'Sun', 'Flame', 'Earth', 'Forest', 'Dream', 'Sky', 'Shadow', 'Flower', 'Ocean', 'River', 'Path', 'Sand', 'Night', 'Star', 'Rain', 'Light', 'Tree', 'Wave', 'Storm', 'Stone', 'Snow', 'Cloud', 'Heart', 'Mountain', 'Leaf', 'Bird', 'Wind', 'Fire', 'Wolf'];
+  return wordList.sort(() => Math.random() - 0.5).slice(0, count);
 }
 
 export function defaultGraph(): GraphModel {

src/components/NodeContextMenu.tsx

@@ -1,11 +1,11 @@
 import { Dropdown, type MenuProps } from "antd";
-import { defaultGraph, graphContext, GraphModel, type EdgeModel, type NodeContext } from "./Graph";
+import { defaultGraph, graphContext, GraphModel, randomWordList, type EdgeModel, type NodeContext } from "./Graph";
 import { useContext } from "react";
 import { cloneDeep } from "lodash";
 import { useGraphsStore } from "../stores/GraphsStore";
 import { useGraphLayersTreeStore } from "../stores/TreeStore";
 
-const items: MenuProps['items'] = [
+const nodeItems: MenuProps['items'] = [
   {
     key: 'rename',
     label: 'Rename',
@@ -23,6 +23,13 @@ const items: MenuProps['items'] = [
   }
 ]
 
+const emptyAreaItems: MenuProps['items'] = [
+  {
+    key: 'create',
+    label: 'Create Node',
+  }
+]
+
 export default function NodeContextMenu({
   nodeContext,
   contextMenuOpened,
@@ -38,9 +45,11 @@ export default function NodeContextMenu({
     return;
   }
 
+  const items = nodeContext.isEmptyArea ? emptyAreaItems : nodeItems;
   const graphContextValue = useContext(graphContext)!;
   const graphsById = useGraphsStore((s) => (s as { graphsById: Map<string, GraphModel> }).graphsById);
   const addTreeNode = useGraphLayersTreeStore(store => store.add);
+  const removeTreeNode = useGraphLayersTreeStore(store => store.remove);
 
   function contextMenuOpenChange(open: boolean) {
     if (!open) {
@@ -56,6 +65,12 @@ export default function NodeContextMenu({
       }
       case 'remove': {
         removeNode(nodeContext.nodeId);
+        removeTreeNode(nodeContext.nodeId);
+        break;
+      }
+      case 'create': {
+        const id = crypto.randomUUID();
+        graphContextValue.setGraph(prev => ({ ...prev, nodes: [...prev.nodes, { id, label: randomWordList(1)[0] }] }));
         break;
       }
       case 'subgraph': {

src/stores/LoadStore.ts

@@ -0,0 +1,11 @@
+import { create } from 'zustand';
+
+interface LoadStore {
+  loadCount: number;
+  signal: () => void;
+}
+
+export const useLoadStore = create<LoadStore>((set) => ({
+  loadCount: 0,
+  signal: () => set((state) => ({ loadCount: state.loadCount + 1 })),
+}));

src/stores/TreeStore.tsx

@@ -10,6 +10,7 @@ export interface TreeStore {
   tree: TreeDataNode[];
   add: (childNode: NodeContext, parentNodeId: string | undefined) => void;
   remove: (nodeId: string) => void;
+  reset: () => void;
 }
 
 export const useGraphLayersTreeStore = create<TreeStore>()((set) => ({
@@ -42,11 +43,12 @@ export const useGraphLayersTreeStore = create<TreeStore>()((set) => ({
     } else {
       const nodesFlatById = new Map(state.nodesFlatById);
       nodesFlatById.set(childNode.key, childNode);
+      const newRootNodes = [...state.rootNodes, childNode];
       const newState = {
         nodesFlatById: nodesFlatById,
         parentIdByChildId: state.parentIdByChildId,
-        rootNodes: [...state.rootNodes, childNode],
-        tree: createTree([...state.rootNodes], nodesFlatById)
+        rootNodes: newRootNodes,
+        tree: createTree(newRootNodes, nodesFlatById)
       }
       return newState;
     }
@@ -87,7 +89,13 @@ export const useGraphLayersTreeStore = create<TreeStore>()((set) => ({
       parentIdByChildId: state.parentIdByChildId,
       tree: createTree([...state.rootNodes], nodesFlatById)
     }
-  })
+  }),
+  reset: () => set({
+    nodesFlatById: new Map<React.Key, TreeDataNode>(),
+    parentIdByChildId: new Map<React.Key, string>(),
+    rootNodes: [],
+    tree: [],
+  }),
 }));
 
 export function createTree(nodes: TreeDataNode[], nodesFlatById: Map<React.Key, TreeDataNode>): TreeDataNode[] {

src/utils/loadGraph.ts

@@ -0,0 +1,64 @@
+import type { GraphModel, NodeContext } from '../components/Graph';
+import { useGraphsStore } from '../stores/GraphsStore';
+import { useGraphLayersTreeStore } from '../stores/TreeStore';
+import { useLoadStore } from '../stores/LoadStore';
+
+interface SavedEdge { id: string; from: string; to: string; }
+interface SavedNode { id: string; label?: string; subgraph?: SavedGraph; }
+interface SavedGraph { id: string; nodes: SavedNode[]; edges: SavedEdge[]; }
+
+function populateStores(
+  graph: SavedGraph,
+  graphsById: Map<string, GraphModel>,
+  treeAdd: (node: NodeContext, parentId: string | undefined) => void,
+): void {
+  graphsById.set(graph.id, {
+    nodes: graph.nodes.map(n => ({ id: n.id, label: n.label })),
+    edges: graph.edges.map(e => ({ id: e.id, from: e.from, to: e.to })),
+  });
+
+  for (const node of graph.nodes) {
+    if (node.subgraph) {
+      const nodeContext: NodeContext = {
+        nodeId: node.id,
+        nodeName: node.label,
+        coords: { x: 0, y: 0 },
+      };
+      treeAdd(nodeContext, graph.id === 'main' ? undefined : graph.id);
+      populateStores(node.subgraph, graphsById, treeAdd);
+    }
+  }
+}
+
+export function loadConceptSketch(): void {
+  const input = document.createElement('input');
+  input.type = 'file';
+  input.accept = '.json,application/json';
+  input.onchange = () => {
+    const file = input.files?.[0];
+    if (!file) return;
+
+    const reader = new FileReader();
+    reader.onload = (e) => {
+      try {
+        const data = JSON.parse(e.target?.result as string) as SavedGraph;
+        if (!data.id || !Array.isArray(data.nodes) || !Array.isArray(data.edges)) {
+          throw new Error('Invalid concept-sketch JSON format');
+        }
+
+        const graphsState = useGraphsStore.getState() as { graphsById: Map<string, GraphModel> };
+        graphsState.graphsById.clear();
+
+        useGraphLayersTreeStore.getState().reset();
+
+        populateStores(data, graphsState.graphsById, useGraphLayersTreeStore.getState().add);
+
+        useLoadStore.getState().signal();
+      } catch (err) {
+        console.error('Failed to load concept sketch:', err);
+      }
+    };
+    reader.readAsText(file);
+  };
+  input.click();
+}

src/utils/saveGraph.ts

@@ -0,0 +1,53 @@
+import type { GraphModel } from '../components/Graph';
+import { useGraphsStore } from '../stores/GraphsStore';
+
+interface SerializedEdge {
+  id: string;
+  from: string;
+  to: string;
+}
+
+interface SerializedNode {
+  id: string;
+  label?: string;
+  subgraph?: SerializedGraph;
+}
+
+interface SerializedGraph {
+  id: string;
+  nodes: SerializedNode[];
+  edges: SerializedEdge[];
+}
+
+function serializeGraph(graphId: string, graphsById: Map<string, GraphModel>): SerializedGraph | null {
+  const graph = graphsById.get(graphId);
+  if (!graph) return null;
+
+  return {
+    id: graphId,
+    nodes: graph.nodes.map(node => {
+      const serialized: SerializedNode = { id: node.id, label: node.label };
+      if (graphsById.has(node.id)) {
+        serialized.subgraph = serializeGraph(node.id, graphsById) ?? undefined;
+      }
+      return serialized;
+    }),
+    edges: graph.edges.map(edge => ({ id: edge.id, from: edge.from, to: edge.to })),
+  };
+}
+
+export function saveConceptSketch(): void {
+  const state = useGraphsStore.getState() as { graphsById: Map<string, GraphModel> };
+  const data = serializeGraph('main', state.graphsById);
+
+  const json = JSON.stringify(data, null, 2);
+  const blob = new Blob([json], { type: 'application/json' });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = 'concept-sketch.json';
+  document.body.appendChild(a);
+  a.click();
+  document.body.removeChild(a);
+  URL.revokeObjectURL(url);
+}