Guard mixed m98m99 staging paths

wasm-port/tests/browser/interp_smoke.html

@@ -7697,6 +7697,7 @@
         ].join("\n"),
       );
 
+      const m98m99MixedSubStylePaths = [];
       for (const mixedSubStyleFixture of [
         {
           name: "called_with_o_call",
@@ -7746,6 +7747,7 @@
           "m98m99/06-error-mixed-sub-styles",
           mixedSubStyleFixture.file,
         );
+        m98m99MixedSubStylePaths.push(mixedSubStylePath);
         const mixedSubStyleRun = runWithCapturedPrints(() =>
           interp.runFile(mixedSubStylePath),
         );
@@ -7772,6 +7774,14 @@
           );
         }
       }
+      const m98m99MixedStagedNgcFiles = [
+        m98m99M98ButNoSubPath,
+        m98m99M98LoopsPath,
+        ...m98m99MixedSubStylePaths,
+      ].map((path) => path.replace("/work/browser-interp/m98m99/", ""));
+      if (m98m99MixedStagedNgcFiles.join(",") !== m98m99RegressionFiles.slice(3, 9).join(",")) {
+        throw new Error("browser_interp_m98m99_mixed_staging_manifest: list drift");
+      }
 
       const m98m99NestedSubsPath = await writeInterpRegressionFile(
         interp,