fix(tests): harden WebMCP evidence capture

Author: miguel-heygen

packages/studio-server/src/helpers/projectSignature.test.ts

@@ -1,5 +1,14 @@
 import { afterEach, describe, expect, it } from "vitest";
-import { mkdtempSync, rmSync, statSync, utimesSync, writeFileSync } from "node:fs";
+import {
+  closeSync,
+  fstatSync,
+  ftruncateSync,
+  futimesSync,
+  mkdtempSync,
+  openSync,
+  rmSync,
+  writeSync,
+} from "node:fs";
 import { tmpdir } from "node:os";
 import { resolve } from "node:path";
 import { affectsProjectSignature, createProjectSignature } from "./projectSignature.js";
@@ -56,13 +65,19 @@ describe("createProjectSignature", () => {
     const project = mkdtempSync(resolve(tmpdir(), "hf-signature-"));
     temporaryProjects.push(project);
     const file = resolve(project, "index.html");
-    writeFileSync(file, "first");
-    const originalMtime = statSync(file).mtime;
-    const before = createProjectSignature(project);
+    const descriptor = openSync(file, "w+");
+    try {
+      writeSync(descriptor, "first");
+      const originalMtime = fstatSync(descriptor).mtime;
+      const before = createProjectSignature(project);
 
-    writeFileSync(file, "other");
-    utimesSync(file, originalMtime, originalMtime);
+      ftruncateSync(descriptor, 0);
+      writeSync(descriptor, "other", 0, "utf8");
+      futimesSync(descriptor, originalMtime, originalMtime);
 
-    expect(createProjectSignature(project)).not.toBe(before);
+      expect(createProjectSignature(project)).not.toBe(before);
+    } finally {
+      closeSync(descriptor);
+    }
   });
 });

packages/studio/tests/e2e/webmcp-edit-loop.mjs

@@ -270,6 +270,31 @@ async function savePreviewScreenshot(page, name) {
   await handle.dispose();
 }
 
+async function saveImageEvidenceFromBrowser(url, evidenceName, contentType) {
+  assert(browser, "Browser is unavailable for image evidence");
+  const evidencePage = await browser.newPage();
+  try {
+    await evidencePage.setViewport({ width: 1200, height: 800, deviceScaleFactor: 1 });
+    await evidencePage.goto(url, {
+      waitUntil: "networkidle0",
+      timeout: RENDER_TIMEOUT_MS,
+    });
+    const image = await evidencePage.waitForSelector("img", {
+      visible: true,
+      timeout: RENDER_TIMEOUT_MS,
+    });
+    assert(image, `Browser did not render image evidence for ${url}`);
+    const outputPath = join(EVIDENCE_DIR, evidenceName);
+    if (contentType.includes("jpeg")) {
+      await image.screenshot({ path: outputPath, type: "jpeg", quality: 92 });
+    } else {
+      await image.screenshot({ path: outputPath, type: "png" });
+    }
+  } finally {
+    await evidencePage.close();
+  }
+}
+
 async function fetchImage(url, evidenceName, expectedContentType = null) {
   const controller = new AbortController();
   const timeout = setTimeout(() => controller.abort(), RENDER_TIMEOUT_MS);
@@ -286,7 +311,7 @@ async function fetchImage(url, evidenceName, expectedContentType = null) {
     }
     const bytes = Buffer.from(await response.arrayBuffer());
     assert(bytes.length > 1_000, `Image evidence was unexpectedly small (${bytes.length} bytes)`);
-    writeFileSync(join(EVIDENCE_DIR, evidenceName), bytes);
+    await saveImageEvidenceFromBrowser(url, evidenceName, contentType);
     return { contentType, sha256: sha256(bytes), size: bytes.length };
   } finally {
     clearTimeout(timeout);
@@ -700,7 +725,6 @@ try {
     error: error instanceof Error ? (error.stack ?? error.message) : String(error),
     serverLogs: serverLogs.join("").slice(-12_000),
   };
-  writeFileSync(join(EVIDENCE_DIR, "failure.json"), `${JSON.stringify(failure, null, 2)}\n`);
   console.error(failure.error);
   process.exitCode = 1;
 } finally {