diff --git a/scripts/run-cross-platform-tests.cjs b/scripts/run-cross-platform-tests.cjs
new file mode 100644
index 000000000..72eb3b1cd
--- /dev/null
+++ b/scripts/run-cross-platform-tests.cjs
@@ -0,0 +1,63 @@
+'use strict';
+
+const { spawnSync } = require('child_process');
+
+const CROSS_PLATFORM_TEST_REASON = Object.freeze({
+  PASS: 'pass',
+  TEST_FAILURE: 'test_failure',
+  INFRA_FAILURE: 'infra_failure',
+  UNKNOWN_FAILURE: 'unknown_failure',
+});
+
+function classify(exitCode, output) {
+  if (exitCode === 0) return CROSS_PLATFORM_TEST_REASON.PASS;
+  if (exitCode === 2 || /infrastructure failure|worktree\.Construct/i.test(output)) {
+    return CROSS_PLATFORM_TEST_REASON.INFRA_FAILURE;
+  }
+  if (/\bFAIL\b|\d+\s+failures?\)/i.test(output)) {
+    return CROSS_PLATFORM_TEST_REASON.TEST_FAILURE;
+  }
+  return CROSS_PLATFORM_TEST_REASON.UNKNOWN_FAILURE;
+}
+
+function runCrossPlatformTests(options = {}, deps = {}) {
+  const {
+    base = 'next',
+    head = 'HEAD',
+    source = '.',
+    targets = 'linux,macos',
+    cwd = process.cwd(),
+  } = options;
+  const runner = deps.spawnSync || spawnSync;
+
+  const args = ['--targets', targets, '--base', base, '--head', head, '--source', source];
+  const result = runner('gsd-test', args, { cwd, encoding: 'utf8' });
+
+  const stdout = result.stdout || '';
+  const stderr = result.stderr || '';
+  const output = `${stdout}\n${stderr}`;
+  const exitCode = Number(result.status ?? 1);
+  const reason = classify(exitCode, output);
+
+  return {
+    ok: exitCode === 0,
+    reason,
+    exitCode,
+    command: ['gsd-test', ...args].join(' '),
+    stdout,
+    stderr,
+  };
+}
+
+if (require.main === module) {
+  const result = runCrossPlatformTests();
+  const line = `[cross-platform-tests] reason=${result.reason} exit=${result.exitCode}`;
+  if (result.ok) {
+    process.stdout.write(`${line}\n`);
+    process.exit(0);
+  }
+  process.stderr.write(`${line}\n`);
+  process.exit(result.exitCode);
+}
+
+module.exports = { CROSS_PLATFORM_TEST_REASON, runCrossPlatformTests };
diff --git a/tests/run-cross-platform-tests.test.cjs b/tests/run-cross-platform-tests.test.cjs
new file mode 100644
index 000000000..d55bb30a8
--- /dev/null
+++ b/tests/run-cross-platform-tests.test.cjs
@@ -0,0 +1,46 @@
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+
+const { CROSS_PLATFORM_TEST_REASON, runCrossPlatformTests } = require('../scripts/run-cross-platform-tests.cjs');
+
+describe('run cross-platform tests module', () => {
+  test('returns pass reason on zero exit', () => {
+    const out = runCrossPlatformTests({}, {
+      spawnSync: () => ({ status: 0, stdout: 'ok', stderr: '' }),
+    });
+    assert.strictEqual(out.ok, true);
+    assert.strictEqual(out.reason, CROSS_PLATFORM_TEST_REASON.PASS);
+    assert.ok(out.command.includes('--base next'));
+  });
+
+  test('classifies infrastructure failure', () => {
+    const out = runCrossPlatformTests({}, {
+      spawnSync: () => ({ status: 2, stdout: '', stderr: 'infrastructure failure' }),
+    });
+    assert.strictEqual(out.ok, false);
+    assert.strictEqual(out.reason, CROSS_PLATFORM_TEST_REASON.INFRA_FAILURE);
+  });
+
+  test('classifies test failure from FAIL marker', () => {
+    const out = runCrossPlatformTests({}, {
+      spawnSync: () => ({ status: 1, stdout: 'linux FAIL 1/2 tests (1 failures)', stderr: '' }),
+    });
+    assert.strictEqual(out.ok, false);
+    assert.strictEqual(out.reason, CROSS_PLATFORM_TEST_REASON.TEST_FAILURE);
+  });
+
+  test('passes options through to command args', () => {
+    let cmd = null;
+    let args = null;
+    runCrossPlatformTests({ base: 'main', head: 'abc123', source: '/tmp/x', targets: 'linux' }, {
+      spawnSync: (c, a) => {
+        cmd = c;
+        args = a;
+        return { status: 0, stdout: '', stderr: '' };
+      },
+    });
+
+    assert.strictEqual(cmd, 'gsd-test');
+    assert.deepStrictEqual(args, ['--targets', 'linux', '--base', 'main', '--head', 'abc123', '--source', '/tmp/x']);
+  });
+});