chore(#4591): add platform-conformance-tier classifier + gate CI on it (#4598)

scripts/lib/suite-detection.cjs

@@ -0,0 +1,32 @@
+'use strict';
+
+/**
+ * Suite classification by filename suffix (#4591 packaging fix — extracted
+ * from scripts/run-tests.cjs so a SHIPPED script, e.g.
+ * scripts/gen-platform-conformance-tier.cjs, can depend on it: run-tests.cjs
+ * itself does not ship (it is a repo-development-only tool), so a shipped
+ * file requiring it directly is MODULE_NOT_FOUND in a published install
+ * (tests/packaging-shipped-scripts-require-only-shipped.test.cjs, #2858).
+ * run-tests.cjs re-exports suiteOf from here unchanged for full backward
+ * compatibility — this is a pure relocation, not a behavior change.
+ *
+ * A file with no suite suffix (plain `foo.test.cjs`) belongs to the `unit`
+ * suite and returns `null` here; a suite-tagged file (`foo.install.test.cjs`)
+ * returns its marker string.
+ */
+
+const { basename } = require('node:path');
+
+const MARKED_SUITES = ['integration', 'install', 'security', 'slow', 'qa'];
+
+function suiteOf(filename) {
+  const name = basename(filename);
+  if (!name.endsWith('.test.cjs')) return null;
+  const base = name.slice(0, -'.test.cjs'.length);
+  const lastDot = base.lastIndexOf('.');
+  if (lastDot === -1) return null;
+  const marker = base.slice(lastDot + 1);
+  return MARKED_SUITES.includes(marker) ? marker : null;
+}
+
+module.exports = { MARKED_SUITES, suiteOf };