fix(release-gate): skip duplicate CI work and stop live LLM blowups

Shared paths like db.mjs were pulling PAGE/DATA live agent suites into every
hotfix. Keep those cases for actual page-data changes, resume passed suites on
the same artifact, and fail fast on Docker/port issues instead of rerunning 100+
scenarios.

Co-authored-by: Cursor <cursoragent@cursor.com>

release-gate/preflight.test.mjs

@@ -0,0 +1,23 @@
+import assert from 'node:assert/strict';
+import net from 'node:net';
+import test from 'node:test';
+
+import { GATE_SUITE_PORTS, assertLoopbackPortAvailable } from './preflight.mjs';
+
+test('gate suites pin isolated loopback ports', () => {
+  assert.equal(GATE_SUITE_PORTS['runtime-sanitized-data-upgrade'], 19085);
+  assert.equal(GATE_SUITE_PORTS['page-data-product-scenarios'], 19086);
+  assert.equal(GATE_SUITE_PORTS['page-content-delivery-scenarios'], 19087);
+});
+
+test('assertLoopbackPortAvailable rejects an occupied port', async () => {
+  const server = net.createServer();
+  await new Promise((resolve) => server.listen(0, '127.0.0.1', resolve));
+  const { port } = server.address();
+  await assert.rejects(
+    () => assertLoopbackPortAvailable(port),
+    /already in use/,
+  );
+  await new Promise((resolve) => server.close(resolve));
+  await assertLoopbackPortAvailable(port);
+});