style: fix extension lint violations

extensions/diffs/src/browser.test.ts

@@ -106,7 +106,7 @@ describe("PlaywrightDiffScreenshotter", () => {
   });
 
   it("renders PDF output when format is pdf", async () => {
-    const { pages, browser, screenshotter } = await createScreenshotterHarness();
+    const { pages, _browser, screenshotter } = await createScreenshotterHarness();
     const pdfPath = path.join(rootDir, "preview.pdf");
 
     await screenshotter.screenshotHtml({

extensions/diffs/src/browser.ts

@@ -258,6 +258,7 @@ export class PlaywrightDiffScreenshotter implements DiffScreenshotter {
       const reason = error instanceof Error ? error.message : String(error);
       throw new Error(
         `Diff PNG/PDF rendering requires a Chromium-compatible browser. Set browser.executablePath or install Chrome/Chromium. ${reason}`,
+        { cause: error },
       );
     } finally {
       await page?.close().catch(() => {});

extensions/diffs/src/tool-render-output.test.ts

@@ -80,7 +80,7 @@ function createApi(): OpenClawPluginApi {
       },
     },
     runtime: {} as OpenClawPluginApi["runtime"],
-  }) as OpenClawPluginApi;
+  });
 }
 
 function createPngScreenshotter(

extensions/diffs/src/tool.test.ts

@@ -485,7 +485,7 @@ function createApi(pluginConfig?: Record<string, unknown>): OpenClawPluginApi {
     },
     pluginConfig,
     runtime: {} as OpenClawPluginApi["runtime"],
-  }) as OpenClawPluginApi;
+  });
 }
 
 function createToolWithScreenshotter(