diff --git a/scripts/demo.ts b/scripts/demo.ts
index 88a6a58..25aecde 100644
--- a/scripts/demo.ts
+++ b/scripts/demo.ts
@@ -1,14 +1,24 @@
 import { spawnSync } from 'node:child_process';
 import { fileURLToPath } from 'node:url';
-import { mkdtempSync, rmSync } from 'node:fs';
+import { mkdtempSync, rmSync, statSync } from 'node:fs';
 import { tmpdir } from 'node:os';
-import { join } from 'node:path';
+import { isAbsolute, join } from 'node:path';
 
 const root = fileURLToPath(new URL('..', import.meta.url));
 const mode = process.argv[2] ?? 'dev';
 let temporary: string | undefined;
 
 try {
+  const npmEntry = process.env.npm_execpath;
+  if (
+    !npmEntry ||
+    !isAbsolute(npmEntry) ||
+    !statSync(npmEntry, { throwIfNoEntry: false })?.isFile()
+  ) {
+    throw new Error(
+      'The demo launcher requires the npm entry supplied by npm. Run "npm run dev" or "npm run build:demo" from the repository root.',
+    );
+  }
   const environment = { ...process.env };
   if (
     environment.CSO_GALLERY_DIRECTORY === undefined &&
@@ -20,8 +30,9 @@ try {
     ).prepareDemoExamples({ directory: temporary });
   }
   const result = spawnSync(
-    'npm',
+    process.execPath,
     [
+      npmEntry,
       'run',
       mode,
       '--workspace',
@@ -33,11 +44,15 @@ try {
       cwd: root,
       stdio: 'inherit',
       env: environment,
+      shell: false,
     },
   );
   if (result.error) {
     throw result.error;
   }
+  if (result.signal) {
+    throw new Error(`Demo npm process terminated by ${result.signal}`);
+  }
   process.exitCode = result.status ?? 1;
 } finally {
   if (temporary) {
diff --git a/tests/integration/demo-launch.test.ts b/tests/integration/demo-launch.test.ts
new file mode 100644
index 0000000..eed53de
--- /dev/null
+++ b/tests/integration/demo-launch.test.ts
@@ -0,0 +1,131 @@
+import { spawnSync } from 'node:child_process';
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { afterEach, expect, test } from 'vitest';
+
+const root = fileURLToPath(new URL('../..', import.meta.url));
+const launcher = join(root, 'scripts/demo.ts');
+const directories: string[] = [];
+
+afterEach(() => {
+  for (const directory of directories.splice(0)) {
+    rmSync(directory, { recursive: true, force: true });
+  }
+});
+
+function fixture() {
+  const directory = mkdtempSync(join(tmpdir(), 'cso npm café '));
+  directories.push(directory);
+  const npmEntry = join(directory, 'npm entry.mjs');
+  const env = { ...process.env };
+  for (const key of Object.keys(env)) {
+    if (
+      [
+        'path',
+        'npm_execpath',
+        'cso_examples_directory',
+        'cso_gallery_directory',
+      ].includes(key.toLowerCase())
+    ) {
+      Reflect.deleteProperty(env, key);
+    }
+  }
+  env.PATH = '';
+  env.npm_execpath = npmEntry;
+  env.PYTHON = join(directory, 'missing-python');
+  return { directory, npmEntry, env };
+}
+
+test.each([
+  ['dev', 'CSO_EXAMPLES_DIRECTORY'],
+  ['build', 'CSO_GALLERY_DIRECTORY'],
+])(
+  'launches %s through the supplied npm entry with %s',
+  (mode, dataVariable) => {
+    const { directory, npmEntry, env } = fixture();
+    env[dataVariable] = directory;
+    writeFileSync(
+      npmEntry,
+      'process.stdout.write(JSON.stringify({ args: process.argv.slice(2), cwd: process.cwd(), examples: process.env.CSO_EXAMPLES_DIRECTORY, gallery: process.env.CSO_GALLERY_DIRECTORY }));',
+    );
+    const forwarded = [
+      '--port',
+      '4123',
+      'a path with spaces',
+      '"quoted" & $HOME; %PATH%',
+      '',
+    ];
+    const result = spawnSync(process.execPath, [launcher, mode, ...forwarded], {
+      cwd: directory,
+      env,
+      encoding: 'utf8',
+      timeout: 30_000,
+    });
+    expect(result.error).toBeUndefined();
+    expect(result.status, result.stderr).toBe(0);
+    expect(JSON.parse(result.stdout)).toEqual({
+      args: ['run', mode, '--workspace', '@cs-object/demo', '--', ...forwarded],
+      cwd: root.replace(/[\\/]$/, ''),
+      ...(dataVariable === 'CSO_EXAMPLES_DIRECTORY'
+        ? { examples: directory }
+        : { gallery: directory }),
+    });
+  },
+);
+
+test('preserves child stderr and nonzero exit status', () => {
+  const { directory, npmEntry, env } = fixture();
+  env.CSO_EXAMPLES_DIRECTORY = directory;
+  writeFileSync(
+    npmEntry,
+    'process.stderr.write("npm child failed\\n"); process.exitCode = 23;',
+  );
+  const result = spawnSync(process.execPath, [launcher, 'build'], {
+    env,
+    encoding: 'utf8',
+    timeout: 30_000,
+  });
+  expect(result.status).toBe(23);
+  expect(result.stderr).toBe('npm child failed\n');
+});
+
+test.skipIf(process.platform === 'win32')(
+  'reports a child terminated by a signal',
+  () => {
+    const { directory, npmEntry, env } = fixture();
+    env.CSO_EXAMPLES_DIRECTORY = directory;
+    writeFileSync(npmEntry, 'process.kill(process.pid, "SIGTERM");');
+    const result = spawnSync(process.execPath, [launcher, 'dev'], {
+      env,
+      encoding: 'utf8',
+      timeout: 30_000,
+    });
+    expect(result.status).toBe(1);
+    expect(result.stderr).toContain('Demo npm process terminated by SIGTERM');
+  },
+);
+
+test.each(['missing', 'empty', 'absent-file', 'directory', 'relative'])(
+  'explains how to launch when the npm entry is %s before preparing examples',
+  (kind) => {
+    const { directory, npmEntry, env } = fixture();
+    if (kind === 'missing') Reflect.deleteProperty(env, 'npm_execpath');
+    if (kind === 'empty') env.npm_execpath = '';
+    if (kind === 'directory') env.npm_execpath = directory;
+    if (kind === 'relative') env.npm_execpath = 'npm entry.mjs';
+    if (kind !== 'absent-file')
+      writeFileSync(npmEntry, 'process.exitCode = 0;');
+    const result = spawnSync(process.execPath, [launcher], {
+      cwd: directory,
+      env,
+      encoding: 'utf8',
+      timeout: 30_000,
+    });
+    expect(result.status).toBe(1);
+    expect(result.stderr).toContain('npm run dev');
+    expect(result.stderr).toContain('npm run build:demo');
+    expect(result.stdout).toBe('');
+  },
+);