test: add buffer independence and SEA VFS coverage tests

Add test verifying MemoryProvider readFileSync returns independent
buffer copies that don't share underlying memory. Add SEA fixture
tests for node:sea API coexistence with VFS and node_modules package
lookups. Use Uint8Array from primordials in SEA provider.

Author: mcollina

lib/internal/vfs/providers/sea.js

@@ -8,6 +8,7 @@ const {
   SafeSet,
   StringPrototypeStartsWith,
   Symbol,
+  Uint8Array,
 } = primordials;
 
 const { Buffer } = require('buffer');

test/fixtures/sea/vfs/sea-config.json

@@ -6,6 +6,8 @@
     "config.json": "config.json",
     "data/greeting.txt": "greeting.txt",
     "modules/math.js": "math.js",
-    "modules/calculator.js": "calculator.js"
+    "modules/calculator.js": "calculator.js",
+    "node_modules/test-pkg/package.json": "test-pkg-package.json",
+    "node_modules/test-pkg/index.js": "test-pkg-index.js"
   }
 }

test/fixtures/sea/vfs/sea.js

@@ -48,4 +48,17 @@ assert.strictEqual(calculator.sum(10, 20), 30, 'calculator.sum should work');
 assert.strictEqual(calculator.product(3, 7), 21, 'calculator.product should work');
 console.log('transitive require from VFS tests passed');
 
+// Test that node:sea API and VFS can load the same asset
+const sea = require('node:sea');
+const seaAsset = sea.getAsset('data/greeting.txt', 'utf8');
+const vfsAsset = fs.readFileSync('/sea/data/greeting.txt', 'utf8');
+assert.strictEqual(seaAsset, vfsAsset, 'node:sea and VFS should return the same content');
+console.log('node:sea API and VFS coexistence test passed');
+
+// Test node_modules package lookup via VFS
+const testPkg = require('test-pkg');
+assert.strictEqual(testPkg.name, 'test-pkg', 'package name should match');
+assert.strictEqual(testPkg.greet('World'), 'Hello, World!', 'package function should work');
+console.log('node_modules package lookup test passed');
+
 console.log('All SEA VFS tests passed!');

test/fixtures/sea/vfs/test-pkg-index.js

@@ -0,0 +1,5 @@
+'use strict';
+module.exports = {
+  name: 'test-pkg',
+  greet: (name) => `Hello, ${name}!`,
+};

test/fixtures/sea/vfs/test-pkg-package.json

@@ -0,0 +1,5 @@
+{
+  "name": "test-pkg",
+  "version": "1.0.0",
+  "main": "index.js"
+}

test/parallel/test-vfs-provider-memory.js

@@ -363,6 +363,28 @@ const vfs = require('node:vfs');
   }, { code: 'EISDIR' });
 }
 
+// Test that readFileSync returns independent buffer copies
+{
+  const myVfs = vfs.create();
+
+  myVfs.writeFileSync('/independent.txt', 'original content');
+
+  const buf1 = myVfs.readFileSync('/independent.txt');
+  const buf2 = myVfs.readFileSync('/independent.txt');
+
+  // Both should have the same content
+  assert.deepStrictEqual(buf1, buf2);
+
+  // Mutating one should not affect the other
+  buf1[0] = 0xFF;
+  assert.notDeepStrictEqual(buf1, buf2);
+  assert.strictEqual(buf2.toString(), 'original content');
+
+  // A third read should still return the original content
+  const buf3 = myVfs.readFileSync('/independent.txt');
+  assert.strictEqual(buf3.toString(), 'original content');
+}
+
 // ==================== Async Operations ====================
 
 // Test async read and write operations