diff --git a/packages/twenty-sdk/src/app-seeds/rich-app/__integration__/app-build/app-build.integration.spec.ts b/packages/twenty-sdk/src/app-seeds/rich-app/__integration__/app-build/app-build.integration.spec.ts
new file mode 100644
index 00000000000..820dd4d3502
--- /dev/null
+++ b/packages/twenty-sdk/src/app-seeds/rich-app/__integration__/app-build/app-build.integration.spec.ts
@@ -0,0 +1,67 @@
+import { readdir, rm } from 'node:fs/promises';
+import { join } from 'path';
+
+import { appBuild } from '@/cli/public-operations/app-build';
+import { pathExists } from '@/cli/utilities/file/fs-utils';
+import { GENERATED_DIR, OUTPUT_DIR } from 'twenty-shared/application';
+
+const APP_PATH = join(__dirname, '../..');
+
+describe('rich-app app:build', () => {
+  let buildResult: Awaited<ReturnType<typeof appBuild>>;
+
+  beforeAll(async () => {
+    const generatedPath = join(
+      APP_PATH,
+      'node_modules',
+      'twenty-sdk',
+      GENERATED_DIR,
+    );
+
+    await rm(generatedPath, { recursive: true, force: true });
+
+    buildResult = await appBuild({ appPath: APP_PATH });
+  }, 60_000);
+
+  it('should complete build successfully', () => {
+    expect(buildResult.success).toBe(true);
+  });
+
+  it('should produce manifest in output directory', async () => {
+    const manifestPath = join(APP_PATH, OUTPUT_DIR, 'manifest.json');
+
+    expect(await pathExists(manifestPath)).toBe(true);
+  });
+
+  it('should produce built logic function files', async () => {
+    const outputDir = join(APP_PATH, OUTPUT_DIR);
+    const files = await readdir(outputDir, { recursive: true });
+    const functionFiles = files
+      .map((file) => file.toString())
+      .filter((file) => file.endsWith('.function.mjs'))
+      .sort();
+
+    expect(functionFiles.length).toBeGreaterThan(0);
+  });
+
+  // app:build only creates client stubs (empty CoreApiClient / MetadataApiClient)
+  // because it doesn't sync with the server or generate the real API client.
+  // Logic functions that use CoreApiClient will get an empty class at runtime.
+  // When this is fixed, update this test to assert the client IS fully generated.
+  // See: https://github.com/twentyhq/twenty/pull/18460
+  it('should only produce client stubs (not a fully generated CoreApiClient)', async () => {
+    const clientIndexPath = join(
+      APP_PATH,
+      'node_modules',
+      'twenty-sdk',
+      GENERATED_DIR,
+      'core',
+      'index.ts',
+    );
+
+    const { readFile } = await import('node:fs/promises');
+    const content = await readFile(clientIndexPath, 'utf-8');
+
+    expect(content).toBe('export class CoreApiClient {}\n');
+  });
+});
diff --git a/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/__e2e__/function-execute.e2e-spec.ts b/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/__e2e__/function-execute.e2e-spec.ts
index 5b5165229aa..e6618e256b1 100644
--- a/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/__e2e__/function-execute.e2e-spec.ts
+++ b/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/__e2e__/function-execute.e2e-spec.ts
@@ -76,4 +76,24 @@ describe('functionExecute E2E', () => {
       error: { code: 'FUNCTION_NOT_FOUND' },
     });
   });
+
+  // Verifies that CoreApiClient is fully generated (not just stubs) after
+  // appGenerateClient. If app:build is used without client generation, the
+  // bundled CoreApiClient would be an empty stub and this test would fail.
+  // See: https://github.com/twentyhq/twenty/pull/18460
+  it('should execute a function that uses CoreApiClient with real query/mutation methods', async () => {
+    const result = await functionExecute({
+      appPath: APP_PATH,
+      functionName: 'check-core-client',
+    });
+
+    expect(result).toMatchObject({
+      success: true,
+      data: {
+        functionName: 'check-core-client',
+        status: 'SUCCESS',
+        data: { hasQuery: true, hasMutation: true },
+      },
+    });
+  });
 });
diff --git a/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/src/logic-functions/check-core-client.function.ts b/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/src/logic-functions/check-core-client.function.ts
new file mode 100644
index 00000000000..6645dd04650
--- /dev/null
+++ b/packages/twenty-sdk/src/cli/__tests__/apps/function-execute-app/src/logic-functions/check-core-client.function.ts
@@ -0,0 +1,26 @@
+import { CoreApiClient } from 'twenty-sdk/generated';
+import { defineLogicFunction } from '@/sdk';
+
+export const CHECK_CORE_CLIENT_UNIVERSAL_IDENTIFIER =
+  'b7c8d9e0-1a2b-4c3d-8e5f-6a7b8c9d0e1f';
+
+const checkCoreClientHandler = () => {
+  const client = new CoreApiClient();
+
+  return {
+    hasQuery: typeof client.query === 'function',
+    hasMutation: typeof client.mutation === 'function',
+  };
+};
+
+export default defineLogicFunction({
+  universalIdentifier: CHECK_CORE_CLIENT_UNIVERSAL_IDENTIFIER,
+  name: 'check-core-client',
+  timeoutSeconds: 5,
+  handler: checkCoreClientHandler,
+  httpRouteTriggerSettings: {
+    path: '/check-core-client',
+    httpMethod: 'GET',
+    isAuthRequired: false,
+  },
+});
diff --git a/packages/twenty-sdk/tsconfig.json b/packages/twenty-sdk/tsconfig.json
index db12e9ed30a..a1005264c31 100644
--- a/packages/twenty-sdk/tsconfig.json
+++ b/packages/twenty-sdk/tsconfig.json
@@ -36,6 +36,8 @@
     "src/front-component-renderer/host/generated/host-component-registry.ts",
     "src/front-component-renderer/remote/generated/remote-components.ts",
     "src/front-component-renderer/remote/generated/remote-elements.ts",
-    "src/front-component-renderer/__stories__/**/*"
+    "src/front-component-renderer/__stories__/**/*",
+    "src/app-seeds/*/src/**/*",
+    "src/cli/__tests__/apps/*/src/**/*"
   ]
 }