diff --git a/wasm-port/docs/compatibility-validation.md b/wasm-port/docs/compatibility-validation.md
index 2240f2c..83e5277 100644
--- a/wasm-port/docs/compatibility-validation.md
+++ b/wasm-port/docs/compatibility-validation.md
@@ -263,9 +263,9 @@ path additionally covers the same canonical-event fixture group, plus
 `position_params` uses a dedicated file-path expectation under
 `tests/fixtures/canon_file/` because LinuxCNC file execution advances the
 post-execute position parameters differently than the line-by-line MDI smoke.
-The same Node WASM file-path smoke also covers the negative fixture group and
-checks the LinuxCNC file-execution error text plus absent canonical motion
-constraints where applicable.
+The same Node WASM and browser file-path smokes also cover the negative fixture
+group and check the LinuxCNC file-execution error text plus absent canonical
+motion constraints where applicable.
 The Node WASM interpreter smoke also covers LinuxCNC parameter-file
 restore/save behavior through the exported C ABI, including out-of-order file
 rejection, missing-file success, required numeric parameter writeback, removal
@@ -375,6 +375,19 @@ Node WASM file-path negative coverage currently includes every fixture under
 - `tool_length_offset_not_found`
 - `tool_not_found`
 
+Browser interpreter file-path negative coverage currently includes the same
+negative fixture list through `Interp::open()`/`read()`/`execute()`:
+
+- `g1_zero_feed`
+- `arc_radius_mismatch`
+- `arc_zero_radius`
+- `cutter_comp_plane_change`
+- `g53_incremental`
+- `namedparam_readonly`
+- `numbered_param_readonly`
+- `tool_length_offset_not_found`
+- `tool_not_found`
+
 Browser interpreter `Interp::execute()` coverage currently includes:
 
 - `minimal_linear`
diff --git a/wasm-port/tests/browser/interp_smoke.html b/wasm-port/tests/browser/interp_smoke.html
index 7911a9c..fac4488 100644
--- a/wasm-port/tests/browser/interp_smoke.html
+++ b/wasm-port/tests/browser/interp_smoke.html
@@ -61,6 +61,35 @@
       }
     }
 
+    function verifyExpectedFileError(fixtureName, output, expectedText) {
+      if (!output.includes("file_open=0")) {
+        throw new Error(`${fixtureName}: missing file_open=0`);
+      }
+
+      const expectedLines = expectedText.split("\n").filter(Boolean);
+      for (const expectedLine of expectedLines) {
+        if (expectedLine.startsWith("absent=")) {
+          const forbidden = expectedLine.slice("absent=".length);
+          if (output.includes(forbidden)) {
+            throw new Error(`${fixtureName}: unexpected ${forbidden}`);
+          }
+          continue;
+        }
+
+        if (expectedLine.startsWith("error_text=")) {
+          const message = expectedLine.slice("error_text=".length);
+          if (!output.includes(`file_error_text=${message}`)) {
+            throw new Error(`${fixtureName}: missing file error ${message}`);
+          }
+          continue;
+        }
+
+        if (expectedLine.startsWith("canon_event=") && !output.includes(expectedLine)) {
+          throw new Error(`${fixtureName}: missing ${expectedLine}`);
+        }
+      }
+    }
+
     async function verifyRejects(fixtureName, operation, expectedPattern) {
       try {
         await operation();
@@ -113,6 +142,19 @@
         );
       }
 
+      for (const errorFixtureName of INTERP_ERROR_FIXTURES) {
+        const programPath = `/work/${errorFixtureName}-error.ngc`;
+        interp.writeTextFile(
+          programPath,
+          await fetchText(`../fixtures/gcode_errors/${errorFixtureName}.ngc`),
+        );
+        verifyExpectedFileError(
+          `${errorFixtureName}_file`,
+          interp.runFile(programPath),
+          (await fetchText(`../fixtures/canon_errors/${errorFixtureName}.expected`)).trimEnd(),
+        );
+      }
+
       const namedParamIniPath = "/work/namedparams.ini";
       const namedParamProgramText = await fetchText(
         `../fixtures/gcode/${INTERP_INI_FIXTURE}.ngc`,