fix(pwa): keep no-store and clinician-share pages out of the page cache

With the service worker now registered for every user, the network-first
page cache sees every authenticated navigation. The everyday app routes
are client-fetch-only shells with no server-rendered PII, but the
`/c/[token]` clinician-share view renders health values straight into the
HTML and emits `no-store`. The page cache ignored the header and stored
it, so a revoked or expired share could still render back offline.

Gate `cache.put` in `networkFirst` on a new `isCacheableNavigation`
check: skip any response carrying `Cache-Control: no-store` (the
principled rule for any present or future server RSC that renders user
data) and skip the `/c/*` path outright as belt-and-braces. Ordinary
navigations still cache unchanged.

public/sw.js

@@ -118,6 +118,32 @@ async function cacheFirst(request, cacheName) {
   return response;
 }
 
+/**
+ * Privacy gate for the navigation page cache. Most app routes are
+ * client-fetch-only shells with no server-rendered PII (health JSON loads
+ * over `/api/*`, which is network-only here), so caching their HTML is
+ * safe. Two carve-outs:
+ *
+ *   1. A `Cache-Control: no-store` response opts itself out — the
+ *      principled, future-proof rule for any current/future server RSC
+ *      that renders user data and sets the header.
+ *   2. `/c/*` (the clinician-share view) renders health values + wellness
+ *      scores straight into the HTML and emits `no-store`; the explicit
+ *      path skip is belt-and-braces so a revoked share can never linger in
+ *      CacheStorage and render back offline.
+ */
+function isCacheableNavigation(request, response) {
+  const cacheControl = response.headers.get("Cache-Control") || "";
+  if (/no-store/i.test(cacheControl)) return false;
+  try {
+    const { pathname } = new URL(request.url);
+    if (pathname === "/c" || pathname.startsWith("/c/")) return false;
+  } catch {
+    // Unparseable URL — fall through; the no-store check already ran.
+  }
+  return true;
+}
+
 /**
  * Network-first: try network (preferring the navigation-preload response
  * when the browser already started it), fall back to cache.
@@ -134,7 +160,7 @@ async function networkFirst(event, cacheName) {
     const response =
       (event.preloadResponse ? await event.preloadResponse : null) ||
       (await fetch(request));
-    if (response.ok) {
+    if (response.ok && isCacheableNavigation(request, response)) {
       const cache = await caches.open(cacheName);
       cache.put(request, response.clone());
       trimCache(cacheName, MAX_PAGE_ENTRIES);

src/__tests__/service-worker.test.ts

@@ -238,6 +238,44 @@ describe("sw.js — networkFirst offline fallback", () => {
   });
 });
 
+describe("sw.js — networkFirst privacy gate", () => {
+  it("does not cache a navigation response that carries Cache-Control: no-store", async () => {
+    const harness = bootServiceWorker();
+    harness.context.fetch = async () =>
+      new Response("private shell", {
+        headers: { "Cache-Control": "no-store" },
+      });
+
+    const res = await dispatchNavigationFetch(harness, "/");
+    expect(await res.clone().text()).toBe("private shell");
+
+    const pages = await harness.cacheStorage.open(CURRENT_PAGE_CACHE);
+    expect(await pages.match(`${ORIGIN}/`)).toBeUndefined();
+  });
+
+  it("does not cache the /c/ clinician-share view even without no-store", async () => {
+    const harness = bootServiceWorker();
+    harness.context.fetch = async () => new Response("share shell");
+
+    const res = await dispatchNavigationFetch(harness, "/c/hls_abc123");
+    expect(await res.clone().text()).toBe("share shell");
+
+    const pages = await harness.cacheStorage.open(CURRENT_PAGE_CACHE);
+    expect(await pages.match(`${ORIGIN}/c/hls_abc123`)).toBeUndefined();
+  });
+
+  it("still caches an ordinary navigation response", async () => {
+    const harness = bootServiceWorker();
+    harness.context.fetch = async () => new Response("app shell");
+
+    const res = await dispatchNavigationFetch(harness, "/measurements");
+    expect(await res.clone().text()).toBe("app shell");
+
+    const pages = await harness.cacheStorage.open(CURRENT_PAGE_CACHE);
+    expect(await pages.match(`${ORIGIN}/measurements`)).toBeDefined();
+  });
+});
+
 describe("sw.js — trimCache", () => {
   it("reads the key list once and deletes only the oldest excess entries", async () => {
     const harness = bootServiceWorker();