vfs: reject useVfs with useSnapshot, useCodeCache, or mainFormat module

Add SEA config validation to error when useVfs is enabled together with
useSnapshot, useCodeCache, or mainFormat: "module", as these combinations
are not supported.

Author: mcollina

doc/api/vfs.md

@@ -753,7 +753,11 @@ file system:
 
 When running as a Single Executable Application (SEA) with `"useVfs": true` in
 the SEA configuration, bundled assets are automatically mounted at `/sea`. No
-additional setup is required:
+additional setup is required.
+
+`"useVfs"` cannot be used together with `"useSnapshot"`, `"useCodeCache"`, or
+`"mainFormat": "module"`. The SEA configuration parser will error if any of
+these combinations are detected.
 
 ```cjs
 // In your SEA entry script

src/node_sea.cc

@@ -565,6 +565,25 @@ std::optional<SeaConfig> ParseSingleExecutableConfig(
     return std::nullopt;
   }
 
+  if (static_cast<bool>(result.flags & SeaFlags::kEnableVfs)) {
+    if (static_cast<bool>(result.flags & SeaFlags::kUseSnapshot)) {
+      FPrintF(stderr,
+              "\"useVfs\" is not supported when \"useSnapshot\" is true\n");
+      return std::nullopt;
+    }
+    if (static_cast<bool>(result.flags & SeaFlags::kUseCodeCache)) {
+      FPrintF(stderr,
+              "\"useVfs\" is not supported when \"useCodeCache\" is true\n");
+      return std::nullopt;
+    }
+    if (result.main_format == ModuleFormat::kModule) {
+      FPrintF(stderr,
+              "\"useVfs\" is not supported when "
+              "\"mainFormat\" is \"module\"\n");
+      return std::nullopt;
+    }
+  }
+
   if (result.main_path.empty()) {
     FPrintF(stderr,
             "\"main\" field of %s is not a non-empty string\n",