vfs: address review feedback for SEA docs and getSeaVfs

- Separate readFileSync calls in SEA VFS example for clarity
- Make getSeaVfs() throw ERR_INVALID_ARG_VALUE if called with a
  different prefix than the first call, preventing subtle bugs

PR-URL: #61478

Author: mcollina

doc/api/single-executable-applications.md

@@ -188,9 +188,11 @@ are accessible through this virtual path.
 const fs = require('node:fs');
 
 // Assets are automatically available at /sea when running as SEA
-const config = JSON.parse(fs.readFileSync('/sea/config.json', 'utf8'));
+const rawConfig = fs.readFileSync('/sea/config.json', 'utf8');
 const data = fs.readFileSync('/sea/data/file.txt');
 
+const config = JSON.parse(rawConfig);
+
 // Directory operations work too
 const files = fs.readdirSync('/sea/assets');
 

lib/internal/vfs/sea.js

@@ -2,9 +2,15 @@
 
 const { isSea, getAssetKeys } = internalBinding('sea');
 const { kEmptyObject, getLazy } = require('internal/util');
+const {
+  codes: {
+    ERR_INVALID_ARG_VALUE,
+  },
+} = require('internal/errors');
 
 // Lazy-loaded VFS
 let cachedSeaVfs = null;
+let cachedSeaVfsPrefix = null;
 
 // Lazy-load VirtualFileSystem and SEAProvider to avoid loading VFS code if not needed
 const lazyVirtualFileSystem = getLazy(
@@ -53,10 +59,20 @@ function createSeaVfs(options = kEmptyObject) {
  * This is a singleton that is lazily created on first access.
  * @param {object} [options] Configuration options (only used on first call)
  * @returns {VirtualFileSystem|null} The VFS instance, or null if not running as SEA
+ * @throws {ERR_INVALID_ARG_VALUE} If called with a different prefix than the first call
  */
 function getSeaVfs(options) {
+  const prefix = options?.prefix ?? '/sea';
+
   if (cachedSeaVfs === null) {
     cachedSeaVfs = createSeaVfs(options);
+    cachedSeaVfsPrefix = prefix;
+  } else if (prefix !== cachedSeaVfsPrefix) {
+    throw new ERR_INVALID_ARG_VALUE(
+      'options.prefix',
+      prefix,
+      `SEA VFS is already initialized with prefix '${cachedSeaVfsPrefix}'`,
+    );
   }
   return cachedSeaVfs;
 }