Run typecheck with the local TypeScript binary so Windows npx does not fetch dummy tsc.

scripts/run-ci.mjs

@@ -296,8 +296,9 @@ async function main() {
   const singleShard = /^\d+\/\d+$/.test(opts.shard) ? opts.shard : '';
 
   if (!opts.skipTypecheck) {
+    const tscJs = path.join(ROOT, 'node_modules', 'typescript', 'bin', 'tsc');
     console.log('[ci] typecheck: tsc --noEmit');
-    const tsc = spawnSync('npx', ['tsc', '--noEmit'], { cwd: ROOT, stdio: 'inherit' });
+    const tsc = spawnSync(process.execPath, [tscJs, '--noEmit'], { cwd: ROOT, stdio: 'inherit' });
     if (tsc.status !== 0) {
       const failSummary = { suite: suite.name, status: 'typecheck_failed', stamp, durationMs: Date.now() - startedAt };
       writeFileSync(path.join(archiveDir, 'summary.json'), JSON.stringify(failSummary, null, 2));