diff --git a/wasm-port/docs/compatibility-validation.md b/wasm-port/docs/compatibility-validation.md
index 27608eb..0b4b61d 100644
--- a/wasm-port/docs/compatibility-validation.md
+++ b/wasm-port/docs/compatibility-validation.md
@@ -295,7 +295,8 @@ restore/save behavior through the exported C ABI, including out-of-order file
 rejection, missing-file success, missing required numeric parameter defaulting,
 required numeric parameter writeback, removal of named-parameter-only lines
 from saved output, and the `.bak` backup produced by vendored
-`save_parameters()`. It also covers LinuxCNC tool-table
+`save_parameters()`, including browser OPFS readback of the backup text after
+the host bridge writes it to persistent storage. It also covers LinuxCNC tool-table
 load/save behavior through vendored `tooldata_common.cc`, including the
 non-random and random-toolchanger `tooldata_init()` branches, with the SDK
 only copying text into the Emscripten filesystem and calling the exported C
diff --git a/wasm-port/tests/browser/interp_smoke.html b/wasm-port/tests/browser/interp_smoke.html
index dc06a57..d074792 100644
--- a/wasm-port/tests/browser/interp_smoke.html
+++ b/wasm-port/tests/browser/interp_smoke.html
@@ -15,6 +15,7 @@
       saveMachineParametersToOpfs,
     } from "../../runtime/opfs/linuxcnc-parameter-bridge.js";
     import {
+      loadTextFile,
       saveTextFile,
     } from "../../runtime/opfs/file-service.js";
     import {
@@ -384,6 +385,23 @@
           "absent=<_named_param>",
         ].join("\n"),
       );
+      if (
+        savedParameters.backupOpfsPath !==
+        "linuxcnc/machines/browser-interp/linuxcnc.var.bak"
+      ) {
+        throw new Error(`unexpected parameter backup path: ${savedParameters.backupOpfsPath}`);
+      }
+      verifyExpectedOutput(
+        "opfs_saved_parameter_backup_text",
+        await loadTextFile(savedParameters.backupOpfsPath),
+        [
+          "5161 10.5",
+          "5162 20.25",
+          "5221 2.25",
+          "5399 44",
+          "<_named_param> 123",
+        ].join("\n"),
+      );
       const savedToolTable = await saveMachineToolTableToOpfs(
         interp,
         "browser-interp",