test: add build smoke test to catch compile failures (#511)

* test: add build smoke test to catch compile failures

Compiles the server binary (darwin-arm64) and verifies --version outputs
the correct version from package.json. Uses an empty resource manifest
and stub env vars so the test runs without R2 access or real secrets.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: address review feedback for PR #511

- Derive build target from process.platform/arch for CI portability
- Include binary stderr in --version assertion for better diagnostics

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/browseros-agent/apps/server/tests/build.test.ts

@@ -0,0 +1,100 @@
+/**
+ * @license
+ * Copyright 2025 BrowserOS
+ *
+ * Build smoke test — compiles the server binary and verifies --version output.
+ * Catches compile failures, broken imports, and version injection bugs.
+ */
+
+import { afterAll, describe, it } from 'bun:test'
+import assert from 'node:assert'
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join, resolve } from 'node:path'
+
+// Derive the build target from the current platform so the test is portable
+function getNativeTarget(): { id: string; ext: string } {
+  const os =
+    process.platform === 'darwin'
+      ? 'darwin'
+      : process.platform === 'win32'
+        ? 'windows'
+        : 'linux'
+  const cpu = process.arch === 'arm64' ? 'arm64' : 'x64'
+  return { id: `${os}-${cpu}`, ext: process.platform === 'win32' ? '.exe' : '' }
+}
+
+// Stub values so the build config validation passes without real secrets
+const BUILD_ENV_STUBS: Record<string, string> = {
+  BROWSEROS_CONFIG_URL: 'https://stub.test/config',
+  CODEGEN_SERVICE_URL: 'https://stub.test/codegen',
+  POSTHOG_API_KEY: 'phc_test_stub',
+  SENTRY_DSN: 'https://stub@sentry.test/0',
+  R2_ACCOUNT_ID: 'test',
+  R2_ACCESS_KEY_ID: 'test',
+  R2_SECRET_ACCESS_KEY: 'test',
+  R2_BUCKET: 'test',
+}
+
+describe('server build', () => {
+  const rootDir = resolve(import.meta.dir, '../../..')
+  const serverPkgPath = resolve(rootDir, 'apps/server/package.json')
+  const buildScript = resolve(rootDir, 'scripts/build/server.ts')
+  const target = getNativeTarget()
+  const binaryPath = resolve(
+    rootDir,
+    `dist/prod/server/.tmp/binaries/browseros-server-${target.id}${target.ext}`,
+  )
+
+  // Empty manifest so the build skips R2 resource downloads
+  const tempDir = mkdtempSync(join(tmpdir(), 'browseros-build-test-'))
+  const emptyManifestPath = join(tempDir, 'empty-manifest.json')
+  writeFileSync(emptyManifestPath, JSON.stringify({ resources: [] }))
+
+  afterAll(() => {
+    rmSync(tempDir, { recursive: true, force: true })
+  })
+
+  it('compiles and --version outputs correct version', async () => {
+    const pkg = await Bun.file(serverPkgPath).json()
+    const expectedVersion: string = pkg.version
+
+    const build = Bun.spawn(
+      [
+        'bun',
+        buildScript,
+        `--target=${target.id}`,
+        '--no-upload',
+        `--manifest=${emptyManifestPath}`,
+      ],
+      {
+        cwd: rootDir,
+        stdout: 'pipe',
+        stderr: 'pipe',
+        env: { ...process.env, ...BUILD_ENV_STUBS },
+      },
+    )
+    const buildExit = await build.exited
+    if (buildExit !== 0) {
+      const stderr = await new Response(build.stderr).text()
+      assert.fail(`Build failed (exit ${buildExit}):\n${stderr}`)
+    }
+
+    const proc = Bun.spawn([binaryPath, '--version'], {
+      stdout: 'pipe',
+      stderr: 'pipe',
+    })
+    const [versionOutput, versionStderr] = await Promise.all([
+      new Response(proc.stdout).text(),
+      new Response(proc.stderr).text(),
+    ])
+    const versionExit = await proc.exited
+
+    assert.strictEqual(
+      versionExit,
+      0,
+      `Binary --version exited non-zero:\n${versionStderr}`,
+    )
+    assert.strictEqual(versionOutput.trim(), expectedVersion)
+  }, 300_000)
+})