diff --git a/scripts/build-diffs-viewer-runtime.mjs b/scripts/build-diffs-viewer-runtime.mjs
index 5d4f739f1fa..d569e4a8ef2 100644
--- a/scripts/build-diffs-viewer-runtime.mjs
+++ b/scripts/build-diffs-viewer-runtime.mjs
@@ -7,6 +7,8 @@ import { build } from "esbuild";
 
 const modulePath = fileURLToPath(import.meta.url);
 const repoRoot = path.resolve(path.dirname(modulePath), "..");
+const pierreDiffsEmptySideEffectNamespace = "openclaw-diffs-empty-side-effect";
+const pierreDiffsEmptySideEffectPath = "pierre-diffs-parse-decorations-side-effect";
 
 const targets = {
   curated: {
@@ -20,6 +22,39 @@ const targets = {
   },
 };
 
+function toPosixPath(value) {
+  return String(value ?? "").replaceAll("\\", "/");
+}
+
+export function createPierreDiffsSideEffectImportPlugin() {
+  return {
+    name: "openclaw-diffs-pierre-side-effect-imports",
+    setup(buildContext) {
+      buildContext.onResolve({ filter: /^diff$/ }, (args) => {
+        const importer = toPosixPath(args.importer);
+        if (!importer.endsWith("/@pierre/diffs/dist/utils/parseDiffDecorations.js")) {
+          return undefined;
+        }
+        return {
+          path: pierreDiffsEmptySideEffectPath,
+          namespace: pierreDiffsEmptySideEffectNamespace,
+          sideEffects: true,
+        };
+      });
+      buildContext.onLoad(
+        {
+          filter: /^pierre-diffs-parse-decorations-side-effect$/,
+          namespace: pierreDiffsEmptySideEffectNamespace,
+        },
+        () => ({
+          contents: "export {};\n",
+          loader: "js",
+        }),
+      );
+    },
+  };
+}
+
 export async function buildDiffsViewerRuntime(targetName) {
   const target = targets[targetName];
   if (!target) {
@@ -44,18 +79,21 @@ export async function buildDiffsViewerRuntime(targetName) {
     legalComments: "none",
     outfile: outputPath,
     write: false,
-    plugins: target.shikiAlias
-      ? [
-          {
-            name: "openclaw-diffs-curated-shiki",
-            setup(buildContext) {
-              buildContext.onResolve({ filter: /^shiki$/ }, () => ({
-                path: path.join(repoRoot, target.shikiAlias),
-              }));
+    plugins: [
+      createPierreDiffsSideEffectImportPlugin(),
+      ...(target.shikiAlias
+        ? [
+            {
+              name: "openclaw-diffs-curated-shiki",
+              setup(buildContext) {
+                buildContext.onResolve({ filter: /^shiki$/ }, () => ({
+                  path: path.join(repoRoot, target.shikiAlias),
+                }));
+              },
             },
-          },
-        ]
-      : [],
+          ]
+        : []),
+    ],
   });
 
   const outputFile = result.outputFiles?.[0];
diff --git a/scripts/test-projects.test-support.mjs b/scripts/test-projects.test-support.mjs
index 82d986c5337..9d48e13cdf1 100644
--- a/scripts/test-projects.test-support.mjs
+++ b/scripts/test-projects.test-support.mjs
@@ -423,6 +423,7 @@ const TOOLING_SOURCE_TEST_TARGETS = new Map([
   ["scripts/test-projects.test-support.mjs", ["test/scripts/test-projects.test.ts"]],
   ["scripts/bundled-plugin-assets.mjs", ["test/scripts/bundled-plugin-assets.test.ts"]],
   ["scripts/bundle-a2ui.mjs", ["test/scripts/bundled-plugin-assets.test.ts"]],
+  ["scripts/build-diffs-viewer-runtime.mjs", ["test/scripts/build-diffs-viewer-runtime.test.ts"]],
   ["extensions/canvas/scripts/bundle-a2ui.mjs", ["extensions/canvas/scripts/bundle-a2ui.test.ts"]],
   ["extensions/canvas/scripts/copy-a2ui.mjs", ["extensions/canvas/scripts/copy-a2ui.test.ts"]],
 ]);
diff --git a/test/scripts/build-diffs-viewer-runtime.test.ts b/test/scripts/build-diffs-viewer-runtime.test.ts
new file mode 100644
index 00000000000..d0a2ba51270
--- /dev/null
+++ b/test/scripts/build-diffs-viewer-runtime.test.ts
@@ -0,0 +1,49 @@
+import { describe, expect, it } from "vitest";
+import { createPierreDiffsSideEffectImportPlugin } from "../../scripts/build-diffs-viewer-runtime.mjs";
+
+type ResolveCallback = (args: { importer: string; path: string }) => unknown;
+type LoadCallback = () => unknown;
+
+function collectPluginCallbacks() {
+  const resolveCallbacks: ResolveCallback[] = [];
+  const loadCallbacks: LoadCallback[] = [];
+  const plugin = createPierreDiffsSideEffectImportPlugin();
+  plugin.setup({
+    onResolve(_options: unknown, callback: ResolveCallback) {
+      resolveCallbacks.push(callback);
+    },
+    onLoad(_options: unknown, callback: LoadCallback) {
+      loadCallbacks.push(callback);
+    },
+  });
+  return { loadCallbacks, resolveCallbacks };
+}
+
+describe("build diffs viewer runtime", () => {
+  it("replaces Pierre Diffs' empty side-effect import without touching real diff imports", () => {
+    const { loadCallbacks, resolveCallbacks } = collectPluginCallbacks();
+    expect(resolveCallbacks).toHaveLength(1);
+    expect(loadCallbacks).toHaveLength(1);
+
+    expect(
+      resolveCallbacks[0]({
+        path: "diff",
+        importer: "/repo/node_modules/@pierre/diffs/dist/utils/parseDiffDecorations.js",
+      }),
+    ).toEqual({
+      path: "pierre-diffs-parse-decorations-side-effect",
+      namespace: "openclaw-diffs-empty-side-effect",
+      sideEffects: true,
+    });
+    expect(
+      resolveCallbacks[0]({
+        path: "diff",
+        importer: "/repo/node_modules/@pierre/diffs/dist/utils/renderDiffWithHighlighter.js",
+      }),
+    ).toBeUndefined();
+    expect(loadCallbacks[0]()).toEqual({
+      contents: "export {};\n",
+      loader: "js",
+    });
+  });
+});