diff --git a/ui/public/sw.js b/ui/public/sw.js
index 9a9d1a7ee65..4f9da070a7a 100644
--- a/ui/public/sw.js
+++ b/ui/public/sw.js
@@ -24,8 +24,9 @@ self.addEventListener("fetch", (event) => {
   const { request } = event;
   const url = new URL(request.url);
 
-  // Skip non-GET requests and API calls
-  if (request.method !== "GET" || url.pathname.startsWith("/api")) {
+  // Explicitly private requests must bypass BOTH cache writes and offline
+  // fallback, including extension endpoints outside the host /api namespace.
+  if (request.method !== "GET" || url.pathname.startsWith("/api") || request.cache === "no-store") {
     return;
   }
 
@@ -33,7 +34,8 @@ self.addEventListener("fetch", (event) => {
   event.respondWith(
     fetch(request)
       .then((response) => {
-        if (response.ok && url.origin === self.location.origin) {
+        const cacheControl = response.headers.get("cache-control") ?? "";
+        if (response.ok && url.origin === self.location.origin && !/(?:^|,)\s*(?:no-store|private)(?:\s*(?:,|=)|\s*$)/i.test(cacheControl)) {
           const clone = response.clone();
           caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
         }
diff --git a/ui/src/lib/service-worker-cache-policy.test.ts b/ui/src/lib/service-worker-cache-policy.test.ts
new file mode 100644
index 00000000000..802be4ef178
--- /dev/null
+++ b/ui/src/lib/service-worker-cache-policy.test.ts
@@ -0,0 +1,43 @@
+// @vitest-environment node
+import { readFileSync } from "node:fs";
+import vm from "node:vm";
+import { describe, expect, it, vi } from "vitest";
+
+function worker() {
+  const handlers = new Map<string, (event: unknown) => void>();
+  const put = vi.fn();
+  const match = vi.fn();
+  const fetch = vi.fn().mockResolvedValue(new Response("public asset"));
+  vm.runInNewContext(readFileSync(new URL("../../public/sw.js", import.meta.url), "utf8"), {
+    self: { location: { origin: "https://example.test" }, addEventListener: (type: string, fn: (event: unknown) => void) => handlers.set(type, fn) },
+    URL, Response, fetch, caches: { open: async () => ({ put }), match },
+  });
+  const request = (cache: RequestCache = "default") => {
+    const respondWith = vi.fn();
+    handlers.get("fetch")!({ request: new Request("https://example.test/extension/history", { cache }), respondWith });
+    return respondWith;
+  };
+  return { request, fetch, put, match };
+}
+
+describe("service worker privacy boundaries", () => {
+  it("bypasses both caching and offline fallback for a no-store request outside /api", () => {
+    const w = worker();
+    expect(w.request("no-store")).not.toHaveBeenCalled();
+    expect(w.fetch).not.toHaveBeenCalled();
+    expect(w.match).not.toHaveBeenCalled();
+    expect(w.put).not.toHaveBeenCalled();
+  });
+  it.each(["no-store", "max-age=0, no-store", "private", 'private="Set-Cookie"', "PRIVATE, max-age=60"])("never caches a response marked %s", async directive => {
+    const w = worker();
+    w.fetch.mockResolvedValue(new Response("personal content", { headers: { "cache-control": directive } }));
+    const response = await w.request().mock.calls[0]![0];
+    expect(await response.text()).toBe("personal content");
+    expect(w.put).not.toHaveBeenCalled();
+  });
+  it("keeps public asset offline caching", async () => {
+    const w = worker();
+    await w.request().mock.calls[0]![0];
+    expect(w.put).toHaveBeenCalledOnce();
+  });
+});