pnpm add @cognite/app-sdk     # or npm/yarn depending on the app

// src/hooks/useHostApp.ts
import { useState, useEffect } from 'react';
import { connectToHostApp, type HostAppAPI } from '@cognite/app-sdk';

export function useHostApp(): HostAppAPI | null {
  const [api, setApi] = useState<HostAppAPI | null>(null);

  useEffect(() => {
    connectToHostApp({ applicationName: 'my-app' })
      .then(({ api: resolvedApi }) => {
        // IMPORTANT: use the updater form here. Comlink proxies are callable
        // objects, so setApi(proxy) causes React to invoke the proxy as a
        // state-updater function — storing a Promise instead of the proxy.
        // setApi(() => proxy) returns the proxy as the new state value.
        setApi(() => resolvedApi);
      })
      .catch(() => {
        // Running outside Fusion — agent features disabled, no-op
      });
  }, []);

  return api;
}

import { type AgentLayoutPayload } from '@cognite/app-sdk';

// Open as sidebar (most common)
await api.sendAgentLayoutMode({ mode: 'sidebar' });

// Other modes
await api.sendAgentLayoutMode({ mode: 'fullscreen' });
await api.sendAgentLayoutMode({ mode: 'closed' });

{api && (
  <button onClick={() => api.sendAgentLayoutMode({ mode: 'sidebar' })}>
    Open Assistant
  </button>
)}

// Open sidebar then inject context
await api.sendAgentLayoutMode({ mode: 'sidebar' });
await api.sendAgentMessage({
  message: `Analyse the schedule for "${itemName}" and suggest how to reduce total duration.`,
  newSession: true,   // clears previous conversation — appropriate for contextual entry points
});

src/features/agent/
  agentActions.ts     — pure factory: (deps) => Action[]
  agentResources.ts   — pure factory: (deps) => Resource[]
  useAgentServer.ts   — useEffect lifecycle hook; calls the factories and registers

// src/features/agent/agentResources.ts
import { createAgentResource } from '@cognite/app-sdk';
import type { StorageService } from '../storage/StorageService';

export function buildAgentResources(storage: StorageService) {
  return [
    createAgentResource({
      uri: 'my-app://current-state',
      name: 'Current application state',
      description:
        'The current list of items visible in the app, their statuses, and any active filters. Read this before answering questions about what the user is looking at.',
      async read() {
        const data = storage.getAll();
        return [{ type: 'json', data }];
      },
    }),
  ];
}

// src/features/agent/agentActions.ts
import { createAgentAction } from '@cognite/app-sdk';
import { z } from 'zod';
import type { DataService } from '../data/DataService';

export function buildAgentActions(dataService: DataService) {
  return [
    createAgentAction({
      name: 'get_item_details',
      description: 'Retrieve full details for a specific item by ID. Returns all fields including history.',
      parameters: z.object({
        item_id: z.string().describe('The ID of the item to retrieve'),
      }),
      async handler({ item_id }) {
        const item = await dataService.getItem(item_id);
        return { content: [{ type: 'json', data: item }] };
      },
    }),
  ];
}

createAgentAction({
  name: 'update_item_status',
  description:
    'Update the status of an item. Call this ONLY when the user has explicitly approved the change. The UI updates immediately.',
  parameters: z.object({
    item_id: z.string().describe('The item to update'),
    status: z.enum(['active', 'closed', 'pending']).describe('The new status'),
  }),
  async handler({ item_id, status }) {
    storage.updateStatus(item_id, status);
    return { content: [{ type: 'json', data: { success: true } }] };
  },
})

// src/features/agent/useAgentServer.ts
import { useEffect } from 'react';
import { createAgentServer, registerAgentServer, type HostAppAPI } from '@cognite/app-sdk';
import { buildAgentActions } from './agentActions';
import { buildAgentResources } from './agentResources';
import { useStorageService } from '../storage/StorageServiceContext';
import { useDataService } from '../data/DataServiceContext';

export function useAgentServer(api: HostAppAPI | null): void {
  const storage = useStorageService();
  const dataService = useDataService();

  useEffect(() => {
    if (!api) return;

    const server = createAgentServer({
      uri: 'my-app',   // namespaced by Fusion with instance ID — no need to be globally unique
      actions: buildAgentActions(dataService),
      resources: buildAgentResources(storage),
    });

    void registerAgentServer(api, server).catch((err: unknown) => {
      console.warn('[agent] registerAgentServer failed:', err);
    });

    return () => {
      void api.unregisterAgentServer('my-app').catch((err: unknown) => {
        console.warn('[agent] unregisterAgentServer failed:', err);
      });
    };
  }, [api, storage, dataService]);
}

// src/App.tsx
function App() {
  const api = useHostApp();
  useAgentServer(api);   // registers resources + actions when api is ready

  return (
    <AppLayout>
      <MainContent />
      {api && (
        <ToolbarButton onClick={() => api.sendAgentLayoutMode({ mode: 'sidebar' })}>
          Open Assistant
        </ToolbarButton>
      )}
    </AppLayout>
  );
}

// agentActions.test.ts
const mockDataService = { getItem: vi.fn().mockResolvedValue({ id: '1', name: 'Test' }) };
const [getItemAction] = buildAgentActions(mockDataService);

const result = await getItemAction.handler({ item_id: '1' });
expect(result.content[0].data).toEqual({ id: '1', name: 'Test' });