test(spec): cast the root-frame read through unknown, and assert presence

`scripts/import-prerequisite.d.mts` is partial by design and declares only the
two loaders, so tsc sees a namespace without the exit-code constants and
refused the direct cast (TS2352) under `check:scripts-typecheck`. The cast now
goes through `unknown`, and the two `typeof` assertions are what stop a
vanished export from reading as `undefined` on both sides of a comparison.

Claude-Session: https://claude.ai/code/session_01UDXER3sdqfeVYpEWZs5mZx
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/spec/scripts/dist-freshness.test.ts

@@ -537,10 +537,19 @@ describe('the prerequisite exit code, and the refusal text that explains it (#19
     // The drift check, against the authority rather than against a copy of it.
     // `packages/spec` already declares `scripts/**` in CROSS_PACKAGE_TEST_INPUTS,
     // so this read is inside a declared radius.
-    const frame = (await import('../../../scripts/import-prerequisite.mjs')) as {
-      EXIT_PREREQUISITE_NOT_MET: number;
-      EXIT_FINDINGS: number;
+    //
+    // ⚠️ The cast goes through `unknown` because `scripts/import-prerequisite.d.mts`
+    // is PARTIAL BY DESIGN — its own header says the exit-code constants are
+    // deliberately omitted from the mirror — so tsc sees a namespace without
+    // them. That is exactly why the two `typeof` assertions are here rather
+    // than implied: without them the cast would make a vanished export read as
+    // `undefined` on both sides of a comparison nobody would notice.
+    const frame = (await import('../../../scripts/import-prerequisite.mjs')) as unknown as {
+      EXIT_PREREQUISITE_NOT_MET?: number;
+      EXIT_FINDINGS?: number;
     };
+    expect(typeof frame.EXIT_PREREQUISITE_NOT_MET).toBe('number');
+    expect(typeof frame.EXIT_FINDINGS).toBe('number');
     expect(EXIT_PREREQUISITE_NOT_MET).toBe(frame.EXIT_PREREQUISITE_NOT_MET);
     expect(EXIT_FINDINGS).toBe(frame.EXIT_FINDINGS);
   });