尽快推进：收紧浏览器后端边界

docs/linuxcnc-browser-app-source-map.md

@@ -37,6 +37,8 @@ must not expand the temporary smoke parser.
 - The app must require OPFS for browser program parsing and call
   `parseFileWithParameterFile(programPath, parameterPath, "linuxcnc", ...)`.
 - The visible backend selector must stay limited to the LinuxCNC RS274 backend.
+- The app must not read the backend selector as a dynamic backend source; it
+  must force `linuxCncBackend` for browser parsing.
 - `test-native.sh`, `test-linuxcnc-source-link.sh`, and `build-wasm.sh` must
   run `./check-linuxcnc-browser-app-source-map.sh` before consuming app-backed
   browser artifacts or source-linked LinuxCNC objects.