test: fix broken typecheck script and add regression test

scripts/typecheck.test.mjs

@@ -0,0 +1,23 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { spawnSync } from 'node:child_process';
+import path from 'node:path';
+import url from 'node:url';
+
+const __dirname = path.dirname(url.fileURLToPath(import.meta.url));
+const repoRoot = path.join(__dirname, '..');
+
+describe('npm run typecheck', () => {
+  it('runs tsc against tsconfig.json without TS5102 (removed baseUrl option)', () => {
+    const result = spawnSync('npx', ['tsc', '--noEmit'], {
+      cwd: repoRoot,
+      encoding: 'utf-8',
+    });
+
+    assert.equal(
+      result.status,
+      0,
+      `tsc exited with ${result.status}:\n${result.stdout}${result.stderr}`,
+    );
+  });
+});

tsconfig.json

@@ -3,7 +3,11 @@
   "extends": "@docusaurus/tsconfig",
   "compilerOptions": {
     "ignoreDeprecations": "6.0",
-    "allowImportingTsExtensions": true
+    "allowImportingTsExtensions": true,
+    // @docusaurus/tsconfig still sets baseUrl, which TS 5.5+ (we're on ~7.0.2)
+    // rejects with TS5102 ("Option 'baseUrl' has been removed"). Overriding it
+    // to null here strips the inherited value from the merged config.
+    "baseUrl": null
   },
   "exclude": [".docusaurus", "build"]
 }