chore: throw error on assetsDir outside outDir

Author: brc-dd

Diff for: src/node/config.ts

@@ -83,6 +83,18 @@ export async function resolveConfig(
     ? normalizePath(path.resolve(root, userConfig.cacheDir))
     : resolve(root, 'cache')
 
+  const resolvedAssetsDir = normalizePath(path.resolve(outDir, assetsDir))
+  if (!resolvedAssetsDir.startsWith(outDir)) {
+    throw new Error(
+      [
+        `assetsDir cannot be set to a location outside of the outDir.`,
+        `outDir: ${outDir}`,
+        `assetsDir: ${assetsDir}`,
+        `resolved: ${resolvedAssetsDir}`
+      ].join('\n  ')
+    )
+  }
+
   // resolve theme path
   const userThemeDir = resolve(root, 'theme')
   const themeDir = (await fs.pathExists(userThemeDir))