diff --git a/extensions/package-vulnerability-scanner/manifest.json b/extensions/package-vulnerability-scanner/manifest.json
index 80c4ca99..bed1b9b6 100644
--- a/extensions/package-vulnerability-scanner/manifest.json
+++ b/extensions/package-vulnerability-scanner/manifest.json
@@ -20,14 +20,14 @@
   },
   "packages": {},
   "files": {
-    "dist/assets/index-CGfl-rCQ.css": {
-      "checksum": "b4dadccacaa63c585d549a30e09ed801"
+    "dist/assets/index-Bd7WoAqv.css": {
+      "checksum": "980b7708188eee5f84707dcc6cf3b01d"
     },
-    "dist/assets/index-SEZBmp0A.js": {
-      "checksum": "5045b070467147359ba4430ff5a5d602"
+    "dist/assets/index-DDPGfFmA.js": {
+      "checksum": "b6d254fb7554759a23d54603d83fd836"
     },
     "dist/index.html": {
-      "checksum": "35a9caef18b056356d5caff6e12b3c10"
+      "checksum": "58ca7cb5afb344897d80bf2bb8a0b1ac"
     },
     "main.py": {
       "checksum": "331f2474111a6280734062de89152bb6"
diff --git a/extensions/package-vulnerability-scanner/src/App.test.ts b/extensions/package-vulnerability-scanner/src/App.test.ts
new file mode 100644
index 00000000..ff697c87
--- /dev/null
+++ b/extensions/package-vulnerability-scanner/src/App.test.ts
@@ -0,0 +1,61 @@
+// @vitest-environment happy-dom
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+import { setActivePinia, createPinia } from "pinia";
+import { mount, flushPromises } from "@vue/test-utils";
+
+import App from "./App.vue";
+
+// A fetch stub that fails every request with a 424 carrying the given detail,
+// as the backend does for the setup cases.
+function stub424(detail: string) {
+  return vi.fn(async () => ({
+    ok: false,
+    status: 424,
+    json: async () => ({ detail }),
+  }));
+}
+
+beforeEach(() => {
+  setActivePinia(createPinia());
+  vi.spyOn(console, "error").mockImplementation(() => {});
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+describe("App setup screen", () => {
+  it("shows the reason when the viewer's session can't be read", async () => {
+    vi.stubGlobal(
+      "fetch",
+      stub424(
+        "Couldn't read your Connect session. In the content settings, on the " +
+          "Access tab, add a Connect Visitor API Key integration under " +
+          "Integrations, to scan content as you.",
+      ),
+    );
+
+    const wrapper = mount(App);
+    await flushPromises();
+
+    expect(wrapper.text()).toContain("Setup");
+    expect(wrapper.text()).toContain("Couldn't read your Connect session");
+  });
+
+  it("shows the reason when the integration is missing", async () => {
+    vi.stubGlobal(
+      "fetch",
+      stub424(
+        "In the content settings, on the Access tab, add a Connect Visitor API " +
+          "Key integration under Integrations, to scan your content.",
+      ),
+    );
+
+    const wrapper = mount(App);
+    await flushPromises();
+
+    expect(wrapper.text()).toContain("add a Connect Visitor API Key");
+    // Each cause shows its own reason, not the other one.
+    expect(wrapper.text()).not.toContain("Couldn't read your Connect session");
+  });
+});
diff --git a/extensions/package-vulnerability-scanner/src/App.vue b/extensions/package-vulnerability-scanner/src/App.vue
index 0a40095e..adcdf774 100644
--- a/extensions/package-vulnerability-scanner/src/App.vue
+++ b/extensions/package-vulnerability-scanner/src/App.vue
@@ -1,7 +1,9 @@
 <script setup lang="ts">
+import { computed } from "vue";
 import VulnerabilityChecker from "./components/VulnerabilityChecker.vue";
 import ContentList from "./components/ContentList.vue";
 import PoweredByFooter from "./components/PoweredByFooter.vue";
+import StatusMessage from "./components/ui/StatusMessage.vue";
 import { useContentStore } from "./stores/content";
 import { useScannerStore } from "./stores/scanner";
 import { useUserStore } from "./stores/user";
@@ -13,25 +15,74 @@ const userStore = useUserStore();
 
 // ContentList fetches vulnerabilities after it gathers the installed packages.
 userStore.fetchCurrentUser().catch(() => {});
-contentStore.fetchContentList();
+contentStore.fetchContentList().catch(() => {});
 
 const loadingMessage = "Fetching your content...";
+
+// The scan needs the viewer's identity, so a missing Visitor API Key integration
+// gates the whole UI behind a setup message (see the stores' setupRequired).
+const setupRequired = computed(
+  () => userStore.setupRequired || contentStore.setupRequired,
+);
+const isLoading = computed(
+  () => contentStore.isLoading || (!userStore.user && !userStore.error),
+);
+// The stores only set setupRequired on a path that also records the error, so
+// the setup screen can show the reason the backend reported (the session
+// couldn't be read, or the integration is missing) rather than a fixed message.
+const errorMessage = computed(
+  () => userStore.error?.message || contentStore.error?.message,
+);
 </script>
 
 <template>
   <div class="flex flex-col min-h-svh">
+    <div
+      v-if="setupRequired"
+      class="grow bg-gray-100 flex items-center justify-center p-4"
+    >
+      <div
+        class="max-w-md w-full bg-white rounded-lg border border-gray-200 shadow-sm p-8"
+      >
+        <h1 class="text-lg font-semibold text-gray-900 text-center">Setup</h1>
+        <p class="mt-4 text-sm leading-relaxed text-gray-600">
+          {{ errorMessage }}
+        </p>
+        <p class="mt-4 text-sm text-gray-500">
+          For more information, see the
+          <a
+            href="https://docs.posit.co/connect/user/oauth-integrations/"
+            class="text-indigo-600 hover:underline"
+            target="_blank"
+            rel="noopener"
+            >OAuth Integrations documentation</a
+          >.
+        </p>
+      </div>
+    </div>
     <LoadingSpinner
-      v-if="contentStore.isLoading || !userStore.user"
+      v-else-if="isLoading"
       class="grow bg-gray-100"
       :message="loadingMessage"
     />
+    <div
+      v-else-if="errorMessage"
+      class="grow bg-gray-100 flex items-center justify-center p-4"
+    >
+      <StatusMessage
+        type="error"
+        message="The scanner couldn't load"
+        :details="errorMessage"
+        class="max-w-md"
+      />
+    </div>
     <main v-else class="flex-1 p-4 md:p-8 bg-gray-100">
       <div class="max-w-4xl mx-auto">
         <VulnerabilityChecker
           v-if="scannerStore.currentContent"
           :content="scannerStore.currentContent"
         />
-        <ContentList :user="userStore.user" v-else />
+        <ContentList v-else-if="userStore.user" :user="userStore.user" />
       </div>
     </main>
 
diff --git a/extensions/package-vulnerability-scanner/src/stores/content.test.ts b/extensions/package-vulnerability-scanner/src/stores/content.test.ts
new file mode 100644
index 00000000..0c2b459e
--- /dev/null
+++ b/extensions/package-vulnerability-scanner/src/stores/content.test.ts
@@ -0,0 +1,78 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+import { setActivePinia, createPinia } from "pinia";
+
+import { useContentStore } from "./content";
+
+function mockFetch(impl: (url: string) => unknown) {
+  const fn = vi.fn(async (url: string) => impl(url));
+  vi.stubGlobal("fetch", fn);
+  return fn;
+}
+
+function ok(body: unknown) {
+  return { ok: true, status: 200, json: async () => body };
+}
+
+beforeEach(() => {
+  setActivePinia(createPinia());
+  vi.spyOn(console, "error").mockImplementation(() => {});
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+  vi.restoreAllMocks();
+});
+
+describe("content store fetchContentList", () => {
+  it("loads the content list and marks it loaded", async () => {
+    mockFetch(() => ok([{ guid: "g1", title: "A" }]));
+    const store = useContentStore();
+
+    await store.fetchContentList();
+
+    expect(store.contentList).toHaveLength(1);
+    expect(store.isContentLoaded).toBe(true);
+    expect(store.isLoading).toBe(false);
+    expect(store.error).toBeNull();
+  });
+
+  it("requests all content when showAllContent is set", async () => {
+    const fetchFn = mockFetch(() => ok([]));
+    const store = useContentStore();
+    store.showAllContent = true;
+
+    await store.fetchContentList();
+
+    expect(fetchFn).toHaveBeenCalledWith("api/content?show_all=true");
+  });
+
+  it("flags setupRequired and rethrows on a 424", async () => {
+    mockFetch(() => ({ ok: false, status: 424 }));
+    const store = useContentStore();
+
+    await expect(store.fetchContentList()).rejects.toThrow("424");
+    expect(store.setupRequired).toBe(true);
+    expect(store.error).not.toBeNull();
+  });
+
+  it("records the error without flagging setup on a non-424 failure", async () => {
+    mockFetch(() => ({ ok: false, status: 500 }));
+    const store = useContentStore();
+
+    await expect(store.fetchContentList()).rejects.toThrow("500");
+    expect(store.setupRequired).toBe(false);
+    expect(store.error).not.toBeNull();
+  });
+
+  it("skips a refetch once loaded unless forced", async () => {
+    const fetchFn = mockFetch(() => ok([{ guid: "g1", title: "A" }]));
+    const store = useContentStore();
+
+    await store.fetchContentList();
+    await store.fetchContentList();
+    expect(fetchFn).toHaveBeenCalledTimes(1);
+
+    await store.fetchContentList(true);
+    expect(fetchFn).toHaveBeenCalledTimes(2);
+  });
+});
diff --git a/extensions/package-vulnerability-scanner/src/stores/content.ts b/extensions/package-vulnerability-scanner/src/stores/content.ts
index d3a4745d..d80b819d 100644
--- a/extensions/package-vulnerability-scanner/src/stores/content.ts
+++ b/extensions/package-vulnerability-scanner/src/stores/content.ts
@@ -1,6 +1,8 @@
 import { defineStore } from "pinia";
 import { ref } from "vue";
 
+import { errorDetail } from "../lib/errorDetail";
+
 export interface ContentListItem {
   guid: string;
   title: string;
@@ -20,6 +22,7 @@ export const useContentStore = defineStore("content", () => {
   const contentList = ref<ContentListItem[]>([]);
   const isLoading = ref(false);
   const error = ref<Error | null>(null);
+  const setupRequired = ref(false);
   const showAllContent = ref(false);
 
   // Track if content has been loaded for the current mode
@@ -33,6 +36,7 @@ export const useContentStore = defineStore("content", () => {
 
     isLoading.value = true;
     error.value = null;
+    setupRequired.value = false;
 
     try {
       const url = showAllContent.value
@@ -41,7 +45,14 @@ export const useContentStore = defineStore("content", () => {
       const response = await fetch(url);
 
       if (!response.ok) {
-        throw new Error(`HTTP error! Status: ${response.status}`);
+        // 424: the Connect Visitor API Key integration this app needs is not configured.
+        if (response.status === 424) setupRequired.value = true;
+        throw new Error(
+          await errorDetail(
+            response,
+            "Couldn't load your content from Connect",
+          ),
+        );
       }
 
       const data = await response.json();
@@ -61,6 +72,7 @@ export const useContentStore = defineStore("content", () => {
     contentList,
     isLoading,
     error,
+    setupRequired,
     isContentLoaded,
     showAllContent,