参考所有分组：保持OPFS备份失败非致命

结论：按 LinuxCNC rs274ngc_pre.cc save_parameters() 中 unlink/link 失败不阻止 rename 主参数文件的语义，OPFS 参数 .bak 写入失败时不让解析保存失败，并避免把目录当作可 unlink 的备份文件删除；未扩展 smoke 解析行为。

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

web/src/wasm-core.js

@@ -141,6 +141,21 @@ async function removeOpfsEntry(workspacePath, relativePath, recursive) {
   }
 }
 
+async function removeOpfsFileEntry(workspacePath, relativePath) {
+  assertRelativePath(relativePath);
+  const parts = relativePath.split("/");
+  const entryName = parts.pop();
+  try {
+    const directory = await getOpfsDirectoryHandle([workspacePath, ...parts].filter(Boolean).join("/"), false);
+    await directory.getFileHandle(entryName, { create: false });
+    await directory.removeEntry(entryName, { recursive: false });
+  } catch (error) {
+    if (error?.name !== "NotFoundError" && error?.name !== "TypeMismatchError") {
+      throw error;
+    }
+  }
+}
+
 async function opfsEntryExists(workspacePath, relativePath) {
   assertRelativePath(relativePath);
   const parts = relativePath.split("/");
@@ -498,7 +513,7 @@ function installOpfsWorkspace(module, options) {
       if (backupData !== null) {
         await writeOpfsFile(workspacePath, `${path}.bak`, backupData);
       } else {
-        await removeOpfsEntry(workspacePath, `${path}.bak`, false);
+        await removeOpfsFileEntry(workspacePath, `${path}.bak`);
       }
       return data;
     },
@@ -712,9 +727,22 @@ export async function createWasmSimulator(moduleOptions = {}) {
         // replacing filename. Browser filesystems may not expose that link
         // through the WASM mirror, so preserve the loaded OPFS file here.
         if (previousParameterFile === null) {
-          await opfs.removeFile(`${parameterPath}.bak`);
+          try {
+            const backupStat = await opfs.stat(`${parameterPath}.bak`);
+            if (backupStat.kind === "file") {
+              await opfs.removeFile(`${parameterPath}.bak`);
+            }
+          } catch (error) {
+            if (error?.name !== "NotFoundError") {
+              throw error;
+            }
+          }
         } else {
-          await opfs.writeFile(`${parameterPath}.bak`, previousParameterFile);
+          try {
+            await opfs.writeFile(`${parameterPath}.bak`, previousParameterFile);
+          } catch (_backupError) {
+            // LinuxCNC treats link(filename, filename + ".bak") failure as non-fatal.
+          }
         }
         return events;
       } finally {