Guard browser OPFS machine file write helper

wasm-port/tests/browser/interp_smoke.html

@@ -4539,6 +4539,12 @@
       verifyExpectedOutput(label, await loadTextFile(opfsPath), expectedText);
     }
 
+    async function writeOpfsMachineFile(machineId, filename, text) {
+      const opfsPath = opfsMachineFilePath(machineId, filename);
+      await saveTextFile(opfsPath, text);
+      return opfsPath;
+    }
+
     function assertOpfsSessionStaging(label, session, machineId, expectedPaths) {
       if (session.machineId !== machineId) {
         throw new Error(`${label}: unexpected machine id ${session.machineId}`);
@@ -9389,8 +9395,9 @@
         browserIniFileTextPaths,
         "browser-ini-file-session",
       );
-      await saveTextFile(
-        "linuxcnc/machines/browser-ini-file-session/browser-custom.var",
+      await writeOpfsMachineFile(
+        "browser-ini-file-session",
+        "browser-custom.var",
         [
           "5161 31.25",
           "5162 62.5",
@@ -9400,8 +9407,9 @@
           "",
         ].join("\n"),
       );
-      await saveTextFile(
-        "linuxcnc/machines/browser-ini-file-session/browser-custom-tool.tbl",
+      await writeOpfsMachineFile(
+        "browser-ini-file-session",
+        "browser-custom-tool.tbl",
         "T8 P8 Z4.5 D0.5 ;browser custom tool\n",
       );
       const loadedIniFileSession = await loadMachineSessionFromOpfs(
@@ -9560,8 +9568,9 @@
         browserIniOverrideTextPaths,
         "browser-ini-override-session",
       );
-      await saveTextFile(
-        "linuxcnc/machines/browser-ini-override-session/browser-explicit.var",
+      await writeOpfsMachineFile(
+        "browser-ini-override-session",
+        "browser-explicit.var",
         [
           "5161 41.25",
           "5162 82.5",
@@ -9571,8 +9580,9 @@
           "",
         ].join("\n"),
       );
-      await saveTextFile(
-        "linuxcnc/machines/browser-ini-override-session/browser-explicit-tool.tbl",
+      await writeOpfsMachineFile(
+        "browser-ini-override-session",
+        "browser-explicit-tool.tbl",
         "T9 P9 Z5.5 D0.625 ;browser explicit tool\n",
       );
       const loadedIniOverrideSession = await loadMachineSessionFromOpfs(