test: verify committed string oracle

- Regenerate the string case oracle with the active Node executable.\n- Compare the checked-in fixture byte-for-byte before native runtime checks.\n- Keep the Linux parseInt ULP allowance scoped to native output.

packages/runtime/test/string.test.ts

@@ -1,5 +1,5 @@
 import { execFile } from "node:child_process";
-import { mkdir } from "node:fs/promises";
+import { mkdir, readFile } from "node:fs/promises";
 import { join } from "node:path";
 import { promisify } from "node:util";
 import { beforeAll, expect, test } from "vitest";
@@ -33,8 +33,10 @@ beforeAll(async () => {
   ]);
 });
 
-// Runs against the committed case file (generated once from Node via
-// gen-string-cases.mjs — see that file to regenerate). Covers UTF-16
+// Runs against the committed case file generated from Node via
+// gen-string-cases.mjs. The test below also verifies the checked-in oracle
+// against the generator, so an accidental stale result cannot be masked by
+// the platform-specific native-runtime allowlist. Covers UTF-16
 // length/charCodeAt/indexOf/includes/startsWith/endsWith/slice/repeat/
 // trim/trimStart/trimEnd/split/padStart/padEnd/charAt plus parseInt over
 // ASCII, Latin-1, CJK, astral, and combining-mark strings, including the
@@ -63,6 +65,17 @@ const LINUX_PARSEINT_ULP: ReadonlyMap<string, string> = new Map([
   ],
 ]);
 
+test("committed string oracle matches Node", async () => {
+  const caseFile = join(testDir, "string-cases.txt");
+  const [{ stdout }, committed] = await Promise.all([
+    execFileAsync(process.execPath, [join(testDir, "gen-string-cases.mjs")], {
+      maxBuffer: 2 * 1024 * 1024,
+    }),
+    readFile(caseFile, "utf8"),
+  ]);
+  expect(committed).toBe(stdout);
+});
+
 test("string methods match Node on committed oracle cases", async () => {
   const r = await execFileAsync(bin, [join(testDir, "string-cases.txt")]).then(
     (v) => ({ stderr: v.stderr }),