feat(intelligence): add Graph Cohesion

app/src/components/intelligence/GraphCohesionPanel.test.tsx

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+import { fireEvent, render, screen } from '@testing-library/react';
+import { describe, expect, it, vi } from 'vitest';
+
+import { computeGraphCohesion } from '../../lib/memory/graphCohesion';
+import type { GraphRelation } from '../../utils/tauriCommands/memory';
+import GraphCohesionPanel from './GraphCohesionPanel';
+
+function rel(subject: string, object: string): GraphRelation {
+  return {
+    namespace: 'n',
+    subject,
+    predicate: 'p',
+    object,
+    attrs: {},
+    updatedAt: 0,
+    evidenceCount: 1,
+    orderIndex: null,
+    documentIds: [],
+    chunkIds: [],
+  };
+}
+
+// Diamond: A-B, A-C, B-C, B-D, C-D. avg clustering 5/6 (0.83), transitivity 0.75.
+const diamond = computeGraphCohesion([
+  rel('A', 'B'),
+  rel('A', 'C'),
+  rel('B', 'C'),
+  rel('B', 'D'),
+  rel('C', 'D'),
+]);
+
+describe('<GraphCohesionPanel />', () => {
+  it('renders the loading skeleton', () => {
+    render(<GraphCohesionPanel result={null} loading />);
+    expect(screen.getByTestId('graph-cohesion-loading')).toBeInTheDocument();
+  });
+
+  it('renders the empty state when there are no nodes', () => {
+    render(<GraphCohesionPanel result={computeGraphCohesion([])} />);
+    expect(screen.getByText('No knowledge graph yet.')).toBeInTheDocument();
+  });
+
+  it('renders an error with a working retry button', () => {
+    const onRetry = vi.fn();
+    render(<GraphCohesionPanel result={null} error="graph unavailable" onRetry={onRetry} />);
+    expect(screen.getByRole('alert').textContent).toMatch(/graph unavailable/);
+    fireEvent.click(screen.getByRole('button', { name: 'Retry' }));
+    expect(onRetry).toHaveBeenCalledTimes(1);
+  });
+
+  it('renders metric tiles, the network averages, and the brokerage ranking', () => {
+    render(<GraphCohesionPanel result={diamond} />);
+    expect(screen.getByText('Entities')).toBeInTheDocument();
+    expect(screen.getByText('Connections')).toBeInTheDocument();
+    expect(screen.getByText('Triangles')).toBeInTheDocument();
+    expect(screen.getByText('Brokers — loosest neighbourhoods')).toBeInTheDocument();
+    // average clustering 5/6 -> 0.83, transitivity 0.75.
+    expect(screen.getByText(/transitivity 0\.75/)).toBeInTheDocument();
+    // the spine nodes B and C cluster at 0.67 (rendered to 2 decimals).
+    expect(screen.getAllByText('0.67')).toHaveLength(2);
+  });
+
+  it('badges a structural hole (clustering 0) as a broker', () => {
+    // Star: X links A, B, C which never connect -> X is a pure broker.
+    const star = computeGraphCohesion([rel('X', 'A'), rel('X', 'B'), rel('X', 'C')]);
+    render(<GraphCohesionPanel result={star} />);
+    expect(screen.getByText('broker')).toBeInTheDocument();
+    expect(screen.getByText('X')).toBeInTheDocument();
+  });
+
+  it('shows the no-brokers note when every entity has fewer than two links', () => {
+    const single = computeGraphCohesion([rel('A', 'B')]);
+    render(<GraphCohesionPanel result={single} />);
+    expect(screen.getByText('No entities with two or more connections yet.')).toBeInTheDocument();
+    // tiles still render (the graph is non-empty), but no ranking table.
+    expect(screen.getByText('Entities')).toBeInTheDocument();
+    expect(screen.queryByText('Brokers — loosest neighbourhoods')).not.toBeInTheDocument();
+  });
+});

app/src/components/intelligence/GraphCohesionPanel.tsx

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+/**
+ * Graph Cohesion — presentational view. Pure: renders the cohesion summary
+ * tiles (entities / connections / triangles), the network averages, and a
+ * brokerage ranking of the loosest-neighbourhood entities. No data fetching,
+ * no clock, no randomness.
+ */
+import { useMemo } from 'react';
+
+import { useT } from '../../lib/i18n/I18nContext';
+import { type CohesionResult, findBrokers } from '../../lib/memory/graphCohesion';
+
+const MAX_ROWS = 25;
+
+interface GraphCohesionPanelProps {
+  result: CohesionResult | null;
+  loading?: boolean;
+  error?: string | null;
+  onRetry?: () => void;
+}
+
+const GraphCohesionPanel = ({ result, loading, error, onRetry }: GraphCohesionPanelProps) => {
+  const { t } = useT();
+
+  const brokers = useMemo(() => (result ? findBrokers(result, MAX_ROWS) : []), [result]);
+
+  const intro = (
+    <div
+      role="note"
+      className="rounded-lg border border-primary-200 dark:border-primary-500/30 bg-primary-50 dark:bg-primary-500/10 px-3 py-2 text-xs text-stone-700 dark:text-neutral-200">
+      <p className="font-medium mb-1">{t('graphCohesion.title')}</p>
+      <p>{t('graphCohesion.intro')}</p>
+    </div>
+  );
+
+  if (loading) {
+    return (
+      <div className="space-y-4">
+        {intro}
+        <div
+          className="space-y-3"
+          role="status"
+          aria-label={t('graphCohesion.loading')}
+          data-testid="graph-cohesion-loading">
+          <div className="grid gap-2 sm:grid-cols-3">
+            {[0, 1, 2].map(i => (
+              <div
+                key={i}
+                className="animate-pulse rounded-lg border border-stone-200 dark:border-neutral-800 bg-stone-50 dark:bg-neutral-800/60 h-16"
+              />
+            ))}
+          </div>
+          {[0, 1, 2, 3].map(i => (
+            <div
+              key={i}
+              className="animate-pulse rounded-lg border border-stone-200 dark:border-neutral-800 bg-stone-50 dark:bg-neutral-800/60 h-8"
+            />
+          ))}
+        </div>
+      </div>
+    );
+  }
+
+  if (error) {
+    return (
+      <div className="space-y-4">
+        {intro}
+        <div className="rounded-lg border border-coral-200 dark:border-coral-500/30 p-4 text-center">
+          <p role="alert" className="text-xs text-coral-700 dark:text-coral-300">
+            {t('graphCohesion.errorPrefix')} {error}
+          </p>
+          {onRetry && (
+            <button
+              type="button"
+              onClick={onRetry}
+              className="mt-2 rounded-lg bg-primary-500 px-3 py-1.5 text-xs font-semibold text-white hover:bg-primary-600">
+              {t('graphCohesion.retry')}
+            </button>
+          )}
+        </div>
+      </div>
+    );
+  }
+
+  if (!result || result.nodes.length === 0) {
+    return (
+      <div className="space-y-4">
+        {intro}
+        <div className="py-8 text-center">
+          <h3 className="text-sm font-semibold text-stone-700 dark:text-neutral-200">
+            {t('graphCohesion.empty')}
+          </h3>
+          <p className="mt-1 text-xs text-stone-500 dark:text-neutral-400">
+            {t('graphCohesion.emptyHint')}
+          </p>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="space-y-4">
+      {intro}
+
+      {/* Metric tiles */}
+      <div className="grid gap-2 sm:grid-cols-3">
+        {[
+          { label: t('graphCohesion.metricEntities'), value: result.nodeCount },
+          { label: t('graphCohesion.metricConnections'), value: result.edgeCount },
+          { label: t('graphCohesion.metricTriangles'), value: result.triangleCount },
+        ].map(tile => (
+          <div
+            key={tile.label}
+            className="rounded-lg border border-stone-200 dark:border-neutral-800 p-3">
+            <div className="text-[10px] uppercase tracking-wider text-stone-400 dark:text-neutral-500">
+              {tile.label}
+            </div>
+            <div className="text-lg font-semibold tabular-nums text-stone-900 dark:text-neutral-100">
+              {tile.value}
+            </div>
+          </div>
+        ))}
+      </div>
+      <p className="text-[11px] text-stone-500 dark:text-neutral-400">
+        {t('graphCohesion.summaryCaption')
+          .replace('{avg}', result.averageClustering.toFixed(2))
+          .replace('{transitivity}', result.transitivity.toFixed(2))}
+      </p>
+
+      {/* Brokerage ranking: loosest neighbourhoods first (structural holes). */}
+      {brokers.length === 0 ? (
+        <p className="py-4 text-center text-xs text-stone-500 dark:text-neutral-400">
+          {t('graphCohesion.noBrokers')}
+        </p>
+      ) : (
+        <section aria-labelledby="graph-cohesion-heading" className="space-y-1">
+          <h3
+            id="graph-cohesion-heading"
+            className="text-xs font-semibold uppercase tracking-wider text-stone-500 dark:text-neutral-400">
+            {t('graphCohesion.rankedHeading')}
+          </h3>
+          <table className="w-full text-left text-[11px] tabular-nums">
+            <thead className="text-stone-400 dark:text-neutral-500">
+              <tr>
+                <th scope="col" className="w-8 py-1 pr-2 font-medium">
+                  {t('graphCohesion.colRank')}
+                </th>
+                <th scope="col" className="py-1 pr-2 font-medium">
+                  {t('graphCohesion.colEntity')}
+                </th>
+                <th scope="col" className="w-1/3 py-1 pr-2 font-medium">
+                  {t('graphCohesion.colCohesion')}
+                </th>
+                <th scope="col" className="w-12 py-1 text-right font-medium">
+                  {t('graphCohesion.colLinks')}
+                </th>
+              </tr>
+            </thead>
+            <tbody>
+              {brokers.map((node, i) => (
+                <tr key={node.id} className="border-t border-stone-100 dark:border-neutral-800/60">
+                  <td className="py-1 pr-2 text-stone-400 dark:text-neutral-500">{i + 1}</td>
+                  <td className="py-1 pr-2 text-stone-800 dark:text-neutral-100 break-words">
+                    {node.id}
+                    {node.localClustering === 0 && (
+                      <span
+                        title={t('graphCohesion.brokerTitle')}
+                        className="ml-1.5 inline-flex items-center rounded px-1 py-0.5 text-[9px] font-semibold uppercase tracking-wider bg-primary-100 dark:bg-primary-500/20 text-primary-700 dark:text-primary-300">
+                        {t('graphCohesion.brokerBadge')}
+                      </span>
+                    )}
+                  </td>
+                  <td className="py-1 pr-2">
+                    <div className="flex items-center gap-2">
+                      <div className="flex-1 h-2 rounded bg-stone-100 dark:bg-neutral-800 overflow-hidden">
+                        <div
+                          className="h-full bg-primary-400/70"
+                          style={{ width: `${node.localClustering * 100}%` }}
+                        />
+                      </div>
+                      <span className="w-10 shrink-0 text-right text-stone-500 dark:text-neutral-400">
+                        {node.localClustering.toFixed(2)}
+                      </span>
+                    </div>
+                  </td>
+                  <td className="py-1 text-right text-stone-500 dark:text-neutral-400">
+                    {node.degree}
+                  </td>
+                </tr>
+              ))}
+            </tbody>
+          </table>
+        </section>
+      )}
+    </div>
+  );
+};
+
+export default GraphCohesionPanel;

app/src/components/intelligence/GraphCohesionTab.test.tsx

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+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { computeGraphCohesion } from '../../lib/memory/graphCohesion';
+import type { GraphRelation } from '../../utils/tauriCommands/memory';
+import GraphCohesionTab from './GraphCohesionTab';
+
+const mockLoadCohesion = vi.fn();
+const mockLoadNamespaces = vi.fn();
+
+vi.mock('../../services/api/graphCohesionApi', () => ({
+  loadCohesion: (...args: unknown[]) => mockLoadCohesion(...args),
+  loadNamespaces: (...args: unknown[]) => mockLoadNamespaces(...args),
+}));
+
+function rel(subject: string, object: string): GraphRelation {
+  return {
+    namespace: 'n',
+    subject,
+    predicate: 'p',
+    object,
+    attrs: {},
+    updatedAt: 0,
+    evidenceCount: 1,
+    orderIndex: null,
+    documentIds: [],
+    chunkIds: [],
+  };
+}
+
+const result = computeGraphCohesion([rel('A', 'B'), rel('B', 'C'), rel('C', 'A')]);
+
+describe('<GraphCohesionTab />', () => {
+  beforeEach(() => {
+    mockLoadCohesion.mockReset();
+    mockLoadNamespaces.mockReset();
+    mockLoadCohesion.mockResolvedValue(result);
+    mockLoadNamespaces.mockResolvedValue([]);
+  });
+
+  it('loads cohesion (all namespaces) on mount and renders the result', async () => {
+    render(<GraphCohesionTab />);
+    expect(mockLoadCohesion).toHaveBeenCalledWith(undefined);
+    await waitFor(() =>
+      expect(screen.getByText('Brokers — loosest neighbourhoods')).toBeInTheDocument()
+    );
+  });
+
+  it('shows the namespace selector and re-queries on change', async () => {
+    mockLoadNamespaces.mockResolvedValueOnce(['work', 'personal']);
+    render(<GraphCohesionTab />);
+    await waitFor(() => screen.getByRole('combobox'));
+    fireEvent.change(screen.getByRole('combobox'), { target: { value: 'work' } });
+    await waitFor(() => expect(mockLoadCohesion).toHaveBeenCalledWith('work'));
+  });
+
+  it('surfaces an error when the load fails', async () => {
+    mockLoadCohesion.mockReset();
+    mockLoadCohesion.mockRejectedValueOnce(new Error('graph unavailable'));
+    render(<GraphCohesionTab />);
+    await waitFor(() => expect(screen.getByRole('alert').textContent).toMatch(/graph unavailable/));
+  });
+});