fix(rspack): ensure implementation path is defined

Author: ScriptedAlchemy

packages/rspack/src/ModuleFederationPlugin.ts

@@ -136,7 +136,8 @@ export class ModuleFederationPlugin implements RspackPluginInstance {
       }).apply(compiler);
     }
 
-    options.implementation = options.implementation || RuntimeToolsPath;
+    const implementationPath = options.implementation || RuntimeToolsPath;
+    options.implementation = implementationPath;
     let disableManifest = options.manifest === false;
     let disableDts = options.dts === false;
 
@@ -166,7 +167,7 @@ export class ModuleFederationPlugin implements RspackPluginInstance {
       for (const candidate of candidates) {
         try {
           return require.resolve(candidate, {
-            paths: [options.implementation],
+            paths: [implementationPath],
           });
         } catch {}
       }