diff --git a/scripts/test_viewer_render_cancellation.py b/scripts/test_viewer_render_cancellation.py
new file mode 100644
index 000000000..570899d17
--- /dev/null
+++ b/scripts/test_viewer_render_cancellation.py
@@ -0,0 +1,203 @@
+#!/usr/bin/env python3
+"""Exercise viewer PDF rendering cancellation in a real JavaScript runtime."""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+import unittest
+from pathlib import Path
+
+
+REPOSITORY_ROOT = Path(__file__).resolve().parents[1]
+VIEWER_SOURCE = REPOSITORY_ROOT / "src/main/resources/static/assets/viewer/viewer.js"
+
+NODE_HARNESS = r"""
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const vm = require("node:vm");
+
+function makeElement(tagName = "div") {
+  return {
+    tagName: tagName.toUpperCase(),
+    hidden: false,
+    disabled: false,
+    textContent: "",
+    className: "",
+    href: "",
+    target: "",
+    rel: "",
+    clientWidth: 800,
+    children: [],
+    style: {},
+    attributes: new Map(),
+    setAttribute(name, value) {
+      this.attributes.set(name, String(value));
+    },
+    getAttribute(name) {
+      return this.attributes.get(name) ?? null;
+    },
+    addEventListener() {},
+    appendChild(child) {
+      this.children.push(child);
+      return child;
+    },
+    querySelector() {
+      return null;
+    },
+    querySelectorAll() {
+      return [];
+    },
+    remove() {},
+    focus() {},
+    getContext() {
+      return {};
+    },
+  };
+}
+
+(async () => {
+  const elements = new Map();
+  const ids = [
+    "doc-meta",
+    "live-status",
+    "error",
+    "error-title",
+    "error-message",
+    "retry-btn",
+    "open-json-link",
+    "preview",
+  ];
+  for (const id of ids) {
+    elements.set(id, makeElement());
+  }
+
+  const documentStub = {
+    getElementById(id) {
+      return elements.get(id) ?? null;
+    },
+    querySelector() {
+      return null;
+    },
+    createElement(tagName) {
+      return makeElement(tagName);
+    },
+  };
+
+  const windowStub = {
+    location: {
+      origin: "https://viewer.example.test",
+      search: "",
+    },
+    setTimeout() {},
+    open() {
+      return null;
+    },
+  };
+
+  const context = {
+    AbortController,
+    URL,
+    URLSearchParams,
+    console,
+    document: documentStub,
+    window: windowStub,
+  };
+  context.globalThis = context;
+  vm.createContext(context);
+
+  const viewerPath = process.argv[1];
+  const viewerSource = fs.readFileSync(viewerPath, "utf8");
+  vm.runInContext(
+    `${viewerSource}\n;globalThis.__viewerTest = { renderPdfInline };`,
+    context,
+    { filename: viewerPath },
+  );
+
+  let renderStarted;
+  const renderStartedPromise = new Promise(resolve => {
+    renderStarted = resolve;
+  });
+  let resolveRender;
+  const renderPromise = new Promise(resolve => {
+    resolveRender = resolve;
+  });
+  const pdfDocument = {
+    numPages: 1,
+    async getPage() {
+      return {
+        getViewport({ scale }) {
+          return { width: 100 * scale, height: 200 * scale };
+        },
+        render() {
+          renderStarted();
+          return { promise: renderPromise };
+        },
+      };
+    },
+    async destroy() {},
+  };
+  context.__pdfJs = {
+    GlobalWorkerOptions: {},
+    getDocument() {
+      return { promise: Promise.resolve(pdfDocument) };
+    },
+  };
+  vm.runInContext(
+    "pdfJsModulePromise = Promise.resolve(globalThis.__pdfJs);",
+    context,
+  );
+
+  const controller = new AbortController();
+  const rendering = context.__viewerTest.renderPdfInline(
+    "/artifacts/document.pdf",
+    controller.signal,
+  );
+
+  // Wait until page.render() starts so the post-render abort boundary is deterministic.
+  await renderStartedPromise;
+  controller.abort();
+  resolveRender();
+  assert.equal(
+    await rendering,
+    false,
+    "an aborted render must report failure",
+  );
+
+  const preview = elements.get("preview");
+  assert.equal(
+    preview.children.length,
+    0,
+    "a superseded PDF render must not publish canvas or metadata",
+  );
+})().catch(error => {
+  console.error(error.stack || String(error));
+  process.exitCode = 1;
+});
+"""
+
+
+class ViewerRenderCancellationTest(unittest.TestCase):
+    """Validate PDF render supersession behavior through the Node.js harness."""
+
+    def test_superseded_pdf_render_does_not_publish(self) -> None:
+        """Abort an in-flight render and require zero stale DOM publication."""
+
+        node = shutil.which("node")
+        self.assertIsNotNone(node, "Node.js is required for the viewer runtime regression")
+        assert node is not None
+
+        result = subprocess.run(
+            [node, "-e", NODE_HARNESS, str(VIEWER_SOURCE)],
+            cwd=REPOSITORY_ROOT,
+            capture_output=True,
+            check=False,
+            text=True,
+            timeout=15,
+        )
+
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/src/main/resources/static/assets/viewer/viewer.js b/src/main/resources/static/assets/viewer/viewer.js
index a998675c7..33ec05397 100644
--- a/src/main/resources/static/assets/viewer/viewer.js
+++ b/src/main/resources/static/assets/viewer/viewer.js
@@ -131,20 +131,36 @@ function getPdfJsModule() {
   return pdfJsModulePromise;
 }
 
-async function renderPdfInline(path) {
+async function renderPdfInline(path, abortSignal) {
   const resolvedPath = resolveSameOriginHttpUrl(path);
   if (resolvedPath === null) {
     throw new Error("PDF preview resource is invalid");
   }
 
+  if (abortSignal?.aborted) {
+    return false;
+  }
+
   const pdfJs = await getPdfJsModule();
+  if (abortSignal?.aborted) {
+    return false;
+  }
+
   const loadingTask = pdfJs.getDocument({
     url: resolvedPath,
     withCredentials: true,
   });
   const pdfDocument = await loadingTask.promise;
   try {
+    if (abortSignal?.aborted) {
+      return false;
+    }
+
     const page = await pdfDocument.getPage(1);
+    if (abortSignal?.aborted) {
+      return false;
+    }
+
     const unscaledViewport = page.getViewport({ scale: 1 });
     const availableWidth = Math.max(320, el.preview.clientWidth - 32);
     const renderScale = Math.min(2, availableWidth / unscaledViewport.width);
@@ -164,6 +180,10 @@ async function renderPdfInline(path) {
     canvas.setAttribute("aria-label", `Rendered first page of a ${pdfDocument.numPages}-page PDF`);
 
     await page.render({ canvasContext: context, viewport }).promise;
+    if (abortSignal?.aborted) {
+      return false;
+    }
+
     el.preview.appendChild(canvas);
 
     const metadata = document.createElement("p");
@@ -172,6 +192,7 @@ async function renderPdfInline(path) {
       ? "Showing the document page."
       : `Showing page 1 of ${pdfDocument.numPages}. Open the artifact for the complete document.`;
     el.preview.appendChild(metadata);
+    return true;
   } finally {
     await pdfDocument.destroy();
   }
@@ -265,12 +286,19 @@ async function poll(docId, abortSignal) {
     clearPreview();
     const path = bootstrap.data.previewResourcePath;
     if (typeof path === "string" && path.endsWith(".pdf")) {
-      await renderPdfInline(path);
+      await renderPdfInline(path, abortSignal);
+      if (abortSignal.aborted) {
+        return;
+      }
     }
     if (typeof path === "string" && path.length > 0) {
       renderPreviewLink(path);
     }
 
+    if (abortSignal.aborted) {
+      return;
+    }
+
     el.preview.setAttribute("aria-busy", "false");
     el.liveStatus.textContent = "Ready.";
     el.retryBtn.disabled = false;
@@ -348,4 +376,4 @@ async function init() {
   start();
 }
 
-void init();
+void init();
\ No newline at end of file