参考所有分组，完成尽量多的内容。禁止顺手扩功能 smoke：锁定OPFS参数保存顺序

结论：按 LinuxCNC rs274ngc_pre.cc save_parameters() 的 .new、.bak、unlink/link/rename 顺序补强 OPFS/app/browser smoke 守卫，并验证临时参数文件不会残留在 OPFS。

docs/linuxcnc-wasm-smoke-source-map.md

@@ -11,6 +11,9 @@ OPFS-only is the required boundary.
 - `src/emc/rs274ngc/rs274ngc_pre.cc` provides `Interp::ini_load()`,
   `Interp::restore_parameters()`, `Interp::save_parameters()`, and `read_text()`
   behavior exercised by Node/browser bridge tests.
+- `src/emc/rs274ngc/rs274ngc_pre.cc` saves parameters by writing
+  `filename + ".new"`, unlinking `filename + ".bak"`, linking the previous file
+  to `filename + ".bak"`, and renaming the temporary file over the main file.
 - `src/emc/rs274ngc/interp_convert.cc` provides `convert_m()` coverage for
   M66 waits and M68 analog output side effects used by generated remap cases.
 - `src/emc/nml_intf/canon.hh` declares the `WAIT()` and