参考所有分组：完善OPFS参数备份桥接

结论：按 LinuxCNC rs274ngc_pre.cc save_parameters()/restore_parameters() 语义，补齐浏览器 OPFS 参数文件 .bak 持久化；未扩展 smoke 解析行为。

验证：./test-native.sh；./test-linuxcnc-source-link.sh；./test-web-wasm-node-smoke.sh；./test-web-wasm-browser-smoke.sh。

web/src/wasm-core.js

@@ -703,10 +703,19 @@ export async function createWasmSimulator(moduleOptions = {}) {
         throw new Error("OPFS workspace is not available for parameter file persistence");
       }
       cleanupLinuxCncParameterFiles(module);
-      await opfs.loadParameterFile(parameterPath);
+      const previousParameterFile = await opfs.loadParameterFile(parameterPath);
       try {
         const events = parseText(program, dialect, options, { keepLinuxCncParameterFiles: true });
         await opfs.persistParameterFile(parameterPath);
+        // LinuxCNC source basis: rs274ngc_pre.cc save_parameters()
+        // links the previous parameter file to filename + ".bak" before
+        // replacing filename. Browser filesystems may not expose that link
+        // through the WASM mirror, so preserve the loaded OPFS file here.
+        if (previousParameterFile === null) {
+          await opfs.removeFile(`${parameterPath}.bak`);
+        } else if (!(await opfs.exists(`${parameterPath}.bak`))) {
+          await opfs.writeFile(`${parameterPath}.bak`, previousParameterFile);
+        }
         return events;
       } finally {
         cleanupLinuxCncParameterFiles(module);