diff --git a/.env.production.example b/.env.production.example
index 0d5f7a2c5..06ff00f4b 100644
--- a/.env.production.example
+++ b/.env.production.example
@@ -521,10 +521,16 @@ API_TOKEN_HMAC_KEY="<openssl rand -hex 32>"
 # LOG_SLOW_THRESHOLD_MS="3000"
 # LOG_INCLUDE_STACK="false"
 
-# Optional log shipping to a Loki instance. LOKI_ENDPOINT is the push URL and
-# is what turns shipping on; the username/password pair is only needed when
-# your Loki sits behind basic auth. Leave all three unset and logs stay on
-# stdout for the Docker log driver to rotate.
+# Optional log shipping to a Loki instance. LOKI_ENDPOINT turns shipping on.
+# Either form works: the base URL (http://loki:3100) or the full push URL
+# (http://loki:3100/loki/api/v1/push). A Loki on your own network is fine,
+# private addresses and internal hostnames included; only link-local and
+# cloud-metadata addresses are refused. The username/password pair is only
+# needed when your Loki sits behind basic auth. When a push fails (Loki down,
+# wrong path, rejected credentials) the app writes one line to stderr naming
+# the Loki origin, the reason and how many events were dropped, at most once
+# every five minutes per reason; the password never appears in it. Leave all
+# three unset and logs stay on stdout for the Docker log driver to rotate.
 # LOKI_ENDPOINT=""
 # LOKI_USERNAME=""
 # LOKI_PASSWORD=""
diff --git a/docker-compose.yml b/docker-compose.yml
index e55a024af..2ad99006b 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -345,10 +345,11 @@ x-healthlog-env: &healthlog_env
   LOG_SAMPLE_RATE: "${LOG_SAMPLE_RATE:-}"
   LOG_SLOW_THRESHOLD_MS: "${LOG_SLOW_THRESHOLD_MS:-}"
   LOG_INCLUDE_STACK: "${LOG_INCLUDE_STACK:-}"
-  # Optional log shipping to a Loki instance. Set LOKI_ENDPOINT to the push
-  # URL to turn it on; the username/password pair is only needed when your
-  # Loki is behind basic auth. Leave all three unset and logs stay on stdout
-  # for the Docker log driver to rotate.
+  # Optional log shipping to a Loki instance. Set LOKI_ENDPOINT to the base
+  # URL or the full push URL to turn it on; a Loki on your own network works.
+  # The username/password pair is only needed when your Loki is behind basic
+  # auth. Push failures show up as a rate-limited line on stderr. Leave all
+  # three unset and logs stay on stdout for the Docker log driver to rotate.
   LOKI_ENDPOINT: "${LOKI_ENDPOINT:-}"
   LOKI_USERNAME: "${LOKI_USERNAME:-}"
   LOKI_PASSWORD: "${LOKI_PASSWORD:-}"
diff --git a/public/sw.js b/public/sw.js
index 8c4284924..67c604453 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -61,6 +61,21 @@ const CURRENT_HEALTHLOG_CACHES = new Set([
   PAGE_CACHE,
   DATA_CACHE,
 ]);
+// Presence marker `src/proxy.ts` sets on every HealthLog page response. See
+// `isForeignNavigationResponse` for why the worker needs it and the proxy for
+// why it carries no version. Keep the name in lockstep with
+// `HEALTHLOG_PAGE_MARKER_HEADER` there.
+const HEALTHLOG_PAGE_MARKER_HEADER = "X-HealthLog-Page";
+// Set as soon as a navigation looks like another app (see
+// `isForeignNavigationResponse`). While it is set the fetch handler declines
+// every request, so the page and its assets come from the network. It is
+// cleared again when `confirmForeignOrigin` finds HealthLog after all, and
+// stays set for the rest of the worker's life when the origin is confirmed
+// foreign and the worker retires.
+let foreignOrigin = false;
+// One confirmation at a time: a burst of navigations must not fire a burst of
+// probes, or race one probe's "HealthLog after all" against another's retire.
+let foreignOriginCheck = null;
 const MAX_STATIC_ENTRIES = 150;
 const MAX_PAGE_ENTRIES = 30;
 const MAX_DATA_ENTRIES = 60;
@@ -168,6 +183,10 @@ self.addEventListener("activate", (event) => {
 
 // ── Fetch: strategy per resource type ────────────────────────────────────────
 self.addEventListener("fetch", (event) => {
+  // The origin serves another app now (see `retireFromForeignOrigin`): no
+  // `respondWith`, no cache, the browser's own fetch for everything.
+  if (foreignOrigin) return;
+
   const { request } = event;
   const url = new URL(request.url);
 
@@ -335,6 +354,134 @@ function isCacheableNavigation(request, response) {
   return true;
 }
 
+/**
+ * Does this navigation response come from something other than HealthLog?
+ *
+ * The worker is registered with scope `/` because HealthLog serves everything
+ * from `/`. When HealthLog is stopped and a different app starts on the same
+ * origin (the usual case is `localhost:3000` on a developer machine), this
+ * worker kept answering: `/_next/static/*` is cache-first, so the other app
+ * ran on HealthLog's cached chunks, and the only way out was unregistering by
+ * hand in the browser's developer tools.
+ *
+ * Only a response that positively looks like another app counts:
+ *
+ *   - a redirect is opaque to the worker (`opaqueredirect`, status 0, no
+ *     readable headers), and HealthLog redirects every signed-out page, so it
+ *     proves nothing; status 0 fails the `ok` check below;
+ *   - a non-2xx answer proves nothing either: a reverse proxy or auth gateway
+ *     in front of a stopped HealthLog answers 502 or 401 without the marker,
+ *     and unregistering there would also drop the Web Push subscription;
+ *   - a network failure never reaches this check (it throws into the offline
+ *     fallback in `networkFirst`).
+ *
+ * What is left is a successful page without the marker HealthLog's proxy puts
+ * on every page response. That is a suspicion, not a verdict: a reverse proxy
+ * with a response-header allowlist strips the marker from every genuine page.
+ * `confirmForeignOrigin` settles it before anything is deleted.
+ */
+function isForeignNavigationResponse(response) {
+  if (!response || !response.ok) return false;
+  return !response.headers.has(HEALTHLOG_PAGE_MARKER_HEADER);
+}
+
+/**
+ * Is the origin positively not HealthLog? Asked of `/api/version`, which is
+ * public (on the proxy's `PUBLIC_PATHS` list, no session needed) and answers
+ * `{ data: { version, buildSha, ... } }`. A body check survives any proxy that
+ * rewrites headers.
+ *
+ * Retire only on a positive answer from something else: a 404, a 2xx that is
+ * not JSON (another app's HTML fallback), or JSON without the HealthLog shape.
+ * `buildSha` is `null` on an image not built by the release workflow, so the
+ * shape is "`version` is a string and `buildSha` is present", not "both are
+ * strings". Anything that is not an answer (a thrown fetch, a 5xx, a 401 from
+ * an auth gateway, a redirect) proves nothing, and the worker resumes normal
+ * service.
+ *
+ * The probe is the worker's own `fetch`, which never passes through this
+ * worker's fetch handler; `no-store` keeps the HTTP cache out of it and
+ * `redirect: "manual"` keeps a login redirect from reading as an answer.
+ */
+async function confirmForeignOrigin() {
+  let response;
+  try {
+    response = await fetch("/api/version", {
+      cache: "no-store",
+      redirect: "manual",
+      credentials: "omit",
+    });
+  } catch {
+    return false;
+  }
+  if (response.status === 404) return true;
+  if (!response.ok) return false;
+  let body;
+  try {
+    body = JSON.parse(await response.text());
+  } catch {
+    return true;
+  }
+  const data = body && typeof body === "object" ? body.data : null;
+  const isHealthlog =
+    !!data &&
+    typeof data === "object" &&
+    typeof data.version === "string" &&
+    "buildSha" in data;
+  return !isHealthlog;
+}
+
+/**
+ * Confirm, then either retire or resume. Shared by concurrent navigations.
+ */
+function checkForeignOrigin() {
+  if (!foreignOriginCheck) {
+    foreignOriginCheck = (async () => {
+      let foreign = false;
+      try {
+        foreign = await confirmForeignOrigin();
+      } catch {
+        foreign = false;
+      }
+      if (foreign) {
+        await retireFromForeignOrigin();
+        return;
+      }
+      // HealthLog after all, or no answer: serve normally again, and let a
+      // later suspicious navigation ask again.
+      foreignOrigin = false;
+      foreignOriginCheck = null;
+    })();
+  }
+  return foreignOriginCheck;
+}
+
+/**
+ * Leave an origin that no longer serves HealthLog: delete every HealthLog
+ * cache (only ours, matched by name, never another app's CacheStorage) and
+ * unregister, so the next load of that origin runs without this worker. The
+ * `foreignOrigin` flag set by the caller covers the requests the current page
+ * still makes before it unloads. Each step is best-effort and independent: a
+ * failed cache delete must not keep the worker registered.
+ */
+async function retireFromForeignOrigin() {
+  try {
+    const keys = await caches.keys();
+    await Promise.all(
+      keys
+        .filter((k) => HEALTHLOG_CACHE_NAME_RE.test(k))
+        .map((k) => caches.delete(k)),
+    );
+  } catch {
+    // CacheStorage unavailable; unregistering still matters more.
+  }
+  try {
+    await self.registration.unregister();
+  } catch {
+    // Nothing further to do from inside the worker.
+  }
+}
+
 /**
  * Network-first: try network (preferring the navigation-preload response
  * when the browser already started it), fall back to cache.
@@ -351,6 +498,13 @@ async function networkFirst(event, cacheName) {
     const response =
       (event.preloadResponse ? await event.preloadResponse : null) ||
       (await fetch(request));
+    if (isForeignNavigationResponse(response)) {
+      // Step aside at once (declining a request only sends it to the
+      // network), but delete nothing until the origin is confirmed foreign.
+      foreignOrigin = true;
+      event.waitUntil(checkForeignOrigin());
+      return response;
+    }
     if (response.ok && isCacheableNavigation(request, response)) {
       event.waitUntil(
         bestEffortCacheWrite(
diff --git a/src/__tests__/proxy-page-marker.test.ts b/src/__tests__/proxy-page-marker.test.ts
new file mode 100644
index 000000000..9c4c897bc
--- /dev/null
+++ b/src/__tests__/proxy-page-marker.test.ts
@@ -0,0 +1,72 @@
+/**
+ * The page marker `public/sw.js` uses to recognise that its origin still
+ * serves HealthLog (#847). A successful navigation without it makes the
+ * worker delete its caches and unregister, so the marker has to be on every
+ * page the proxy lets through, signed in or not, and it must never carry a
+ * version.
+ */
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/process-type", () => ({
+  shouldRunWeb: () => true,
+}));
+
+import { HEALTHLOG_PAGE_MARKER_HEADER, proxy } from "../proxy";
+
+beforeEach(() => {
+  vi.stubEnv("NODE_ENV", "production");
+});
+
+afterEach(() => {
+  vi.unstubAllEnvs();
+});
+
+function request(pathname: string, signedIn = true): NextRequest {
+  return new NextRequest(`http://localhost${pathname}`, {
+    headers: signedIn
+      ? { cookie: "healthlog_session=sess-1", accept: "text/html" }
+      : { accept: "text/html" },
+  });
+}
+
+describe("proxy.ts page marker for the service worker", () => {
+  it.each(["/", "/measurements", "/settings/profile", "/c/hls_abc123"])(
+    "marks the signed-in page %s",
+    (path) => {
+      const res = proxy(request(path));
+      expect(res.headers.get(HEALTHLOG_PAGE_MARKER_HEADER)).toBe("1");
+    },
+  );
+
+  it.each(["/auth/login", "/privacy", "/onboarding"])(
+    "marks the public page %s",
+    (path) => {
+      const res = proxy(request(path, false));
+      expect(res.headers.get(HEALTHLOG_PAGE_MARKER_HEADER)).toBe("1");
+    },
+  );
+
+  it.each(["/api/version", "/api/measurements", "/api/auth/me"])(
+    "leaves the API response %s unmarked",
+    (path) => {
+      const res = proxy(request(path));
+      expect(res.headers.has(HEALTHLOG_PAGE_MARKER_HEADER)).toBe(false);
+    },
+  );
+
+  it("carries presence only, never a version or build id", () => {
+    vi.stubEnv("NEXT_PUBLIC_APP_VERSION", "9.9.9");
+    const res = proxy(request("/"));
+    expect(res.headers.get(HEALTHLOG_PAGE_MARKER_HEADER)).toBe("1");
+  });
+
+  it("uses the header name public/sw.js checks", () => {
+    const sw = readFileSync(resolve(process.cwd(), "public/sw.js"), "utf8");
+    expect(sw).toContain(
+      `const HEALTHLOG_PAGE_MARKER_HEADER = "${HEALTHLOG_PAGE_MARKER_HEADER}";`,
+    );
+  });
+});
diff --git a/src/__tests__/service-worker.test.ts b/src/__tests__/service-worker.test.ts
index ec749ab7b..0ec33c658 100644
--- a/src/__tests__/service-worker.test.ts
+++ b/src/__tests__/service-worker.test.ts
@@ -14,6 +14,11 @@
  *      `event.preloadResponse` when the browser supplies it;
  *   4. `trimCache` reads the key list once and deletes the excess prefix
  *      in a single pass (the previous loop re-fetched all keys per delete).
+ *
+ * A HealthLog page response carries the `X-HealthLog-Page` marker the proxy
+ * sets, so the navigation fixtures below build pages with `healthlogPage()`.
+ * A successful page without it is another app on the same origin (#847),
+ * which the "foreign origin" block covers.
  */
 import { describe, it, expect } from "vitest";
 import { readFileSync } from "node:fs";
@@ -38,6 +43,15 @@ const CURRENT_PAGE_CACHE = `healthlog-pages-${FALLBACK_VERSION}`;
 const CURRENT_STATIC_CACHE = `healthlog-static-${FALLBACK_VERSION}`;
 const CURRENT_DATA_CACHE = `healthlog-data-${FALLBACK_VERSION}`;
 
+const PAGE_MARKER = "X-HealthLog-Page";
+
+/** A page response as HealthLog's proxy delivers it: marker included. */
+function healthlogPage(body: string, init: ResponseInit = {}): Response {
+  const headers = new Headers(init.headers);
+  headers.set(PAGE_MARKER, "1");
+  return new Response(body, { ...init, headers });
+}
+
 class FakeCache {
   map = new Map<string, Response>();
   keysCalls = 0;
@@ -121,6 +135,7 @@ interface SwHarness {
   listeners: Map<string, (event: unknown) => void>;
   cacheStorage: FakeCacheStorage;
   navPreload: { enabled: boolean; enable: () => Promise<void> };
+  unregisterCalls: { count: number };
   lifetimePromises: Promise<unknown>[];
   context: Record<string, unknown>;
 }
@@ -129,6 +144,7 @@ function bootServiceWorker(): SwHarness {
   const listeners = new Map<string, (event: unknown) => void>();
   const cacheStorage = new FakeCacheStorage();
   const lifetimePromises: Promise<unknown>[] = [];
+  const unregisterCalls = { count: 0 };
   const navPreload = {
     enabled: false,
     enable: async () => {
@@ -147,6 +163,10 @@ function bootServiceWorker(): SwHarness {
     clients: { claim: async () => {} },
     registration: {
       navigationPreload: navPreload,
+      unregister: async () => {
+        unregisterCalls.count += 1;
+        return true;
+      },
       showNotification: async (title: string, opts: { tag?: string }) => {
         shown.push({ title, tag: opts?.tag, closed: false });
       },
@@ -194,7 +214,14 @@ function bootServiceWorker(): SwHarness {
   };
   vm.createContext(context);
   vm.runInContext(SW_SOURCE, context);
-  return { listeners, cacheStorage, navPreload, lifetimePromises, context };
+  return {
+    listeners,
+    cacheStorage,
+    navPreload,
+    unregisterCalls,
+    lifetimePromises,
+    context,
+  };
 }
 
 async function dispatchActivate(harness: SwHarness): Promise<void> {
@@ -389,7 +416,7 @@ describe("sw.js — best-effort cache writes", () => {
     const harness = bootServiceWorker();
     const pageCache = await harness.cacheStorage.open(CURRENT_PAGE_CACHE);
     pageCache.putError = new Error("CacheStorage quota exceeded");
-    const networkResponse = new Response("network shell", {
+    const networkResponse = healthlogPage("network shell", {
       headers: { "X-Network-Response": "original" },
     });
     harness.context.fetch = async () => networkResponse;
@@ -413,7 +440,7 @@ describe("sw.js — best-effort cache writes", () => {
       notifyPutStarted = resolve;
     });
     pageCache.onPut = notifyPutStarted;
-    const networkResponse = new Response("network shell");
+    const networkResponse = healthlogPage("network shell");
     harness.context.fetch = async () => networkResponse;
 
     const responsePromise = dispatchNavigationFetch(harness, "/measurements");
@@ -572,7 +599,7 @@ describe("sw.js — networkFirst offline fallback", () => {
     const res = await dispatchNavigationFetch(
       harness,
       "/",
-      Promise.resolve(new Response("preloaded shell")),
+      Promise.resolve(healthlogPage("preloaded shell")),
     );
 
     expect(await res.clone().text()).toBe("preloaded shell");
@@ -587,7 +614,7 @@ 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", {
+      healthlogPage("private shell", {
         headers: { "Cache-Control": "no-store" },
       });
 
@@ -600,7 +627,7 @@ describe("sw.js — networkFirst privacy gate", () => {
 
   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");
+    harness.context.fetch = async () => healthlogPage("share shell");
 
     const res = await dispatchNavigationFetch(harness, "/c/hls_abc123");
     expect(await res.clone().text()).toBe("share shell");
@@ -611,7 +638,7 @@ describe("sw.js — networkFirst privacy gate", () => {
 
   it("still caches an ordinary navigation response", async () => {
     const harness = bootServiceWorker();
-    harness.context.fetch = async () => new Response("app shell");
+    harness.context.fetch = async () => healthlogPage("app shell");
 
     const res = await dispatchNavigationFetch(harness, "/measurements");
     expect(await res.clone().text()).toBe("app shell");
@@ -621,6 +648,375 @@ describe("sw.js — networkFirst privacy gate", () => {
   });
 });
 
+/**
+ * Dispatch any request and report whether the worker took it. Used where the
+ * assertion IS whether `respondWith` was called: a declined request goes to
+ * the network through the browser, untouched by this worker.
+ */
+function dispatchAnyFetch(
+  harness: SwHarness,
+  path: string,
+  headers: Record<string, string> = {},
+): { responded: boolean; response: Promise<Response> | null } {
+  let captured: Promise<Response> | null = null;
+  let responded = false;
+  harness.listeners.get("fetch")!({
+    request: new Request(`${ORIGIN}${path}`, { headers }),
+    respondWith: (p: Promise<Response>) => {
+      responded = true;
+      captured = p;
+    },
+    waitUntil: (p: Promise<unknown>) => {
+      harness.lifetimePromises.push(p);
+    },
+  });
+  return { responded, response: captured };
+}
+
+const HEALTHLOG_VERSION_BODY = JSON.stringify({
+  data: { version: "1.38.21", buildSha: null, builtAt: null },
+  error: null,
+});
+
+/**
+ * Route the harness `fetch`: `/api/version` (the worker's confirmation probe)
+ * gets `version`, everything else gets `page`. Records every requested path.
+ */
+function routeFetch(
+  harness: SwHarness,
+  page: () => Response,
+  version: () => Response | Promise<Response>,
+): string[] {
+  const calls: string[] = [];
+  harness.context.fetch = async (input: RequestInfo | URL) => {
+    const url = new URL(
+      typeof input === "string" || input instanceof URL ? input : input.url,
+      ORIGIN,
+    );
+    calls.push(url.pathname);
+    return url.pathname === "/api/version" ? version() : page();
+  };
+  return calls;
+}
+
+const foreignHtml = () =>
+  new Response("<html>another app</html>", {
+    headers: { "Content-Type": "text/html" },
+  });
+
+async function seedHealthlogCaches(harness: SwHarness): Promise<void> {
+  const statics = await harness.cacheStorage.open(CURRENT_STATIC_CACHE);
+  await statics.put(
+    `${ORIGIN}/_next/static/chunks/app.js`,
+    new Response("healthlog chunk"),
+  );
+  const pages = await harness.cacheStorage.open(CURRENT_PAGE_CACHE);
+  await pages.put(`${ORIGIN}/`, healthlogPage("healthlog shell"));
+  const legacy = await harness.cacheStorage.open("healthlog-data-v0.0.1");
+  await legacy.put(`${ORIGIN}/api/version`, new Response("{}"));
+  // CacheStorage the other app owns on the same origin.
+  const other = await harness.cacheStorage.open("next-app-runtime");
+  await other.put(`${ORIGIN}/x`, new Response("theirs"));
+}
+
+describe("sw.js — foreign origin (#847)", () => {
+  it("keeps serving and caching while the page carries the HealthLog marker", async () => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    harness.context.fetch = async () => healthlogPage("fresh shell");
+
+    const res = await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(await res.text()).toBe("fresh shell");
+    expect(harness.unregisterCalls.count).toBe(0);
+    expect(harness.cacheStorage.stores.has(CURRENT_STATIC_CACHE)).toBe(true);
+    const asset = dispatchAnyFetch(harness, "/_next/static/chunks/app.js");
+    expect(asset.responded).toBe(true);
+    expect(await (await asset.response!).text()).toBe("healthlog chunk");
+  });
+
+  it("retires when the page lacks the marker and the version probe finds another app's HTML", async () => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    const foreignPage = foreignHtml();
+    const calls = routeFetch(harness, () => foreignPage, foreignHtml);
+
+    const res = await dispatchNavigationFetch(harness, "/");
+
+    // The other app's page is returned untouched, and the worker declines
+    // requests at once, before the probe has answered.
+    expect(res).toBe(foreignPage);
+    expect(
+      dispatchAnyFetch(harness, "/_next/static/chunks/app.js").responded,
+    ).toBe(false);
+
+    await Promise.all(harness.lifetimePromises);
+
+    expect(calls).toEqual(["/", "/api/version"]);
+    expect(harness.unregisterCalls.count).toBe(1);
+    // Every HealthLog cache is gone, current and legacy; the other app's is not.
+    expect([...harness.cacheStorage.stores.keys()]).toEqual([
+      "next-app-runtime",
+    ]);
+
+    // Still declining after the retire: static, HTML and API all go to the
+    // network through the browser.
+    expect(
+      dispatchAnyFetch(harness, "/_next/static/chunks/app.js").responded,
+    ).toBe(false);
+    expect(
+      dispatchAnyFetch(harness, "/about", { accept: "text/html" }).responded,
+    ).toBe(false);
+    expect(dispatchAnyFetch(harness, "/api/measurements").responded).toBe(
+      false,
+    );
+  });
+
+  it("retires when the version probe answers 404", async () => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    routeFetch(
+      harness,
+      foreignHtml,
+      () => new Response("Not Found", { status: 404 }),
+    );
+
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(harness.unregisterCalls.count).toBe(1);
+    expect(harness.cacheStorage.stores.has(CURRENT_STATIC_CACHE)).toBe(false);
+  });
+
+  it("retires when the version probe answers JSON without the HealthLog shape", async () => {
+    const harness = bootServiceWorker();
+    routeFetch(
+      harness,
+      foreignHtml,
+      () => new Response(JSON.stringify({ version: "3.0.0" })),
+    );
+
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(harness.unregisterCalls.count).toBe(1);
+  });
+
+  it("probes with no-store and a manual redirect", async () => {
+    const harness = bootServiceWorker();
+    let probeInit: RequestInit | undefined;
+    harness.context.fetch = async (
+      input: RequestInfo | URL,
+      init?: RequestInit,
+    ) => {
+      const path = new URL(
+        String(input instanceof Request ? input.url : input),
+        ORIGIN,
+      ).pathname;
+      if (path === "/api/version") {
+        probeInit = init;
+        return new Response(HEALTHLOG_VERSION_BODY);
+      }
+      return foreignHtml();
+    };
+
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(probeInit?.cache).toBe("no-store");
+    expect(probeInit?.redirect).toBe("manual");
+  });
+
+  it("does not retire when a header-stripping proxy hides the marker from a real HealthLog", async () => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    // The page is HealthLog's, minus the marker a proxy allowlist removed.
+    routeFetch(
+      harness,
+      () => new Response("healthlog page without marker"),
+      () =>
+        new Response(HEALTHLOG_VERSION_BODY, {
+          headers: { "Content-Type": "application/json" },
+        }),
+    );
+
+    const res = await dispatchNavigationFetch(harness, "/");
+    expect(await res.text()).toBe("healthlog page without marker");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(harness.unregisterCalls.count).toBe(0);
+    expect(harness.cacheStorage.stores.has(CURRENT_STATIC_CACHE)).toBe(true);
+    // Normal service resumed: the cached chunk is served cache-first again.
+    const asset = dispatchAnyFetch(harness, "/_next/static/chunks/app.js");
+    expect(asset.responded).toBe(true);
+    expect(await (await asset.response!).text()).toBe("healthlog chunk");
+  });
+
+  it.each([
+    [
+      "the probe throws (network)",
+      () => Promise.reject(new TypeError("network down")),
+    ],
+    ["the probe answers 500", () => new Response("boom", { status: 500 })],
+    [
+      "the probe answers 401 from an auth gateway",
+      () => new Response("Unauthorized", { status: 401 }),
+    ],
+  ])(
+    "does not retire when %s, and resumes service",
+    async (_label, version) => {
+      const harness = bootServiceWorker();
+      await seedHealthlogCaches(harness);
+      routeFetch(harness, foreignHtml, version as () => Promise<Response>);
+
+      await dispatchNavigationFetch(harness, "/");
+      await Promise.all(harness.lifetimePromises);
+
+      expect(harness.unregisterCalls.count).toBe(0);
+      expect(harness.cacheStorage.stores.has(CURRENT_STATIC_CACHE)).toBe(true);
+      expect(
+        dispatchAnyFetch(harness, "/_next/static/chunks/app.js").responded,
+      ).toBe(true);
+    },
+  );
+
+  it("asks again on a later suspicious navigation after an inconclusive probe", async () => {
+    const harness = bootServiceWorker();
+    let probeStatus = 503;
+    const calls = routeFetch(harness, foreignHtml, () =>
+      probeStatus === 503
+        ? new Response("down", { status: 503 })
+        : new Response("Not Found", { status: 404 }),
+    );
+
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+    expect(harness.unregisterCalls.count).toBe(0);
+
+    probeStatus = 404;
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(calls.filter((p) => p === "/api/version")).toHaveLength(2);
+    expect(harness.unregisterCalls.count).toBe(1);
+  });
+
+  it("recognises a foreign page delivered through navigation preload", async () => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    const calls = routeFetch(
+      harness,
+      () => healthlogPage("unexpected"),
+      () => new Response("Not Found", { status: 404 }),
+    );
+
+    const res = await dispatchNavigationFetch(
+      harness,
+      "/",
+      Promise.resolve(new Response("another app")),
+    );
+    await Promise.all(harness.lifetimePromises);
+
+    expect(await res.text()).toBe("another app");
+    // The page came from the preload; the only network call is the probe.
+    expect(calls).toEqual(["/api/version"]);
+    expect(harness.unregisterCalls.count).toBe(1);
+  });
+
+  it("still unregisters when deleting the caches fails", async () => {
+    const harness = bootServiceWorker();
+    harness.cacheStorage.keys = async () => {
+      throw new Error("CacheStorage unavailable");
+    };
+    routeFetch(harness, foreignHtml, foreignHtml);
+
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(harness.unregisterCalls.count).toBe(1);
+  });
+
+  it("keeps the offline fallback when the network fails (HealthLog is down, not replaced)", async () => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    // Default harness fetch throws: network down.
+
+    const res = await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(await res.text()).toBe("healthlog shell");
+    expect(harness.unregisterCalls.count).toBe(0);
+    expect(harness.cacheStorage.stores.has(CURRENT_STATIC_CACHE)).toBe(true);
+  });
+
+  it.each([
+    [
+      "an error page from HealthLog itself",
+      healthlogPage("boom", { status: 500 }),
+    ],
+    [
+      "a gateway error from a proxy in front of a stopped HealthLog",
+      new Response("Bad Gateway", { status: 502 }),
+    ],
+    [
+      "a 401 from an auth gateway",
+      new Response("Unauthorized", { status: 401 }),
+    ],
+  ])("does not treat %s as foreign", async (_label, response) => {
+    const harness = bootServiceWorker();
+    await seedHealthlogCaches(harness);
+    harness.context.fetch = async () => response;
+
+    const res = await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(res).toBe(response);
+    expect(harness.unregisterCalls.count).toBe(0);
+    expect(
+      dispatchAnyFetch(harness, "/_next/static/chunks/app.js").responded,
+    ).toBe(true);
+  });
+
+  it("does not treat an opaque redirect (a signed-out HealthLog page) as foreign", async () => {
+    const harness = bootServiceWorker();
+    const redirect = Response.redirect(`${ORIGIN}/auth/login`, 307);
+    // A navigation fetched with `redirect: "manual"` surfaces as an opaque
+    // redirect in a real worker; model the type the worker sees.
+    Object.defineProperty(redirect, "type", { value: "opaqueredirect" });
+    Object.defineProperty(redirect, "headers", { value: new Headers() });
+    Object.defineProperty(redirect, "ok", { value: false });
+    harness.context.fetch = async () => redirect;
+
+    await dispatchNavigationFetch(harness, "/");
+    await Promise.all(harness.lifetimePromises);
+
+    expect(harness.unregisterCalls.count).toBe(0);
+  });
+
+  it("leaves the one-shot auth navigation path unchanged", async () => {
+    const harness = bootServiceWorker();
+    let fetchCalls = 0;
+    harness.context.fetch = async () => {
+      fetchCalls += 1;
+      return new Response("network callback");
+    };
+
+    const { responded, response } = dispatchAuthNavigation(
+      harness,
+      "/api/auth/oidc/callback?code=abc&state=xyz",
+      Promise.resolve(new Response("preloaded callback")),
+    );
+
+    expect(responded).toBe(true);
+    expect(await (await response!).text()).toBe("preloaded callback");
+    expect(fetchCalls).toBe(0);
+    // An auth response has no page marker and must not retire the worker.
+    await Promise.all(harness.lifetimePromises);
+    expect(harness.unregisterCalls.count).toBe(0);
+  });
+});
+
 describe("sw.js — trimCache", () => {
   it("reads the key list once and deletes only the oldest excess entries", async () => {
     const harness = bootServiceWorker();
diff --git a/src/lib/logging/__tests__/transports-loki.test.ts b/src/lib/logging/__tests__/transports-loki.test.ts
new file mode 100644
index 000000000..a234d8aa4
--- /dev/null
+++ b/src/lib/logging/__tests__/transports-loki.test.ts
@@ -0,0 +1,352 @@
+/**
+ * Loki shipping (#947 follow-up): the endpoint forms an operator types, the
+ * dial path a private Loki needs, the floor no configuration opens, and the
+ * stderr notice that replaces the silent catch.
+ *
+ * Two layers. The mocked-`safeFetch` block pins what the transport asks for
+ * and what it says when that fails. The loopback block runs the real
+ * `safeFetch` against a real HTTP server on 127.0.0.1, which is the case the
+ * public-host pin used to refuse: an address that is not public at all.
+ */
+import { createServer, type Server } from "node:http";
+import type { AddressInfo } from "node:net";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { resetLoggingConfig } from "../config";
+import type { WideEvent } from "../types";
+
+const safeFetchMock = vi.hoisted(() => vi.fn());
+const useRealSafeFetch = vi.hoisted(() => ({ value: false }));
+
+vi.mock("@/lib/safe-fetch", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/safe-fetch")>();
+  return {
+    ...actual,
+    safeFetch: (...args: Parameters<typeof actual.safeFetch>) =>
+      useRealSafeFetch.value
+        ? actual.safeFetch(...args)
+        : safeFetchMock(...args),
+  };
+});
+
+import { SafeFetchError } from "@/lib/safe-fetch";
+import {
+  _resetLokiTransportForTests,
+  emitEvent,
+  flushLokiBuffer,
+  LOKI_FAILURE_NOTICE_INTERVAL_MS,
+  resolveLokiPushTarget,
+} from "../transports";
+
+const USERNAME = "loki-user";
+const PASSWORD = "s3cret-loki-password";
+const BASIC = Buffer.from(`${USERNAME}:${PASSWORD}`).toString("base64");
+
+function makeEvent(): WideEvent {
+  return {
+    timestamp: new Date().toISOString(),
+    duration_ms: 1,
+    request_id: "req-loki",
+    trace_id: "trace-loki",
+    level: "info",
+    kind: "http",
+    service: "healthlog",
+    environment: "test",
+  };
+}
+
+let stderrLines: string[];
+let stderrSpy: ReturnType<typeof vi.spyOn>;
+let stdoutSpy: ReturnType<typeof vi.spyOn>;
+
+function configure(endpoint: string, withAuth = true): void {
+  vi.stubEnv("LOKI_ENDPOINT", endpoint);
+  vi.stubEnv("LOKI_USERNAME", withAuth ? USERNAME : "");
+  vi.stubEnv("LOKI_PASSWORD", withAuth ? PASSWORD : "");
+  resetLoggingConfig();
+}
+
+function buffer(count: number): void {
+  for (let i = 0; i < count; i++) emitEvent(makeEvent());
+}
+
+beforeEach(() => {
+  _resetLokiTransportForTests();
+  safeFetchMock.mockReset();
+  useRealSafeFetch.value = false;
+  stderrLines = [];
+  stderrSpy = vi
+    .spyOn(process.stderr, "write")
+    .mockImplementation((chunk: string | Uint8Array) => {
+      stderrLines.push(String(chunk));
+      return true;
+    });
+  stdoutSpy = vi.spyOn(process.stdout, "write").mockReturnValue(true);
+});
+
+afterEach(() => {
+  stderrSpy.mockRestore();
+  stdoutSpy.mockRestore();
+  vi.unstubAllEnvs();
+  vi.useRealTimers();
+  resetLoggingConfig();
+  _resetLokiTransportForTests();
+});
+
+describe("resolveLokiPushTarget", () => {
+  it.each([
+    ["http://loki:3100", "http://loki:3100/loki/api/v1/push"],
+    ["http://loki:3100/", "http://loki:3100/loki/api/v1/push"],
+    ["http://loki:3100/loki/api/v1/push", "http://loki:3100/loki/api/v1/push"],
+    ["http://loki:3100/loki/api/v1/push/", "http://loki:3100/loki/api/v1/push"],
+    [
+      "https://logs.example.com/tenant-a",
+      "https://logs.example.com/tenant-a/loki/api/v1/push",
+    ],
+    [
+      "https://logs.example.com/tenant-a/loki/api/v1/push",
+      "https://logs.example.com/tenant-a/loki/api/v1/push",
+    ],
+    ["  http://10.0.0.5:3100  ", "http://10.0.0.5:3100/loki/api/v1/push"],
+  ])("%s pushes to %s", (endpoint, expected) => {
+    const resolved = resolveLokiPushTarget(endpoint);
+    expect(resolved.ok).toBe(true);
+    if (resolved.ok) expect(resolved.target.url).toBe(expected);
+  });
+
+  it("approves exactly the endpoint origin, private addresses included", () => {
+    const resolved = resolveLokiPushTarget("http://192.168.1.20:3100/");
+    expect(resolved).toEqual({
+      ok: true,
+      target: {
+        url: "http://192.168.1.20:3100/loki/api/v1/push",
+        origin: "http://192.168.1.20:3100",
+      },
+    });
+  });
+
+  it.each([
+    "http://169.254.169.254",
+    "http://169.254.10.1:3100",
+    "http://0.0.0.0:3100",
+    "http://[fe80::1]:3100",
+  ])("refuses the never-grantable host %s", (endpoint) => {
+    const resolved = resolveLokiPushTarget(endpoint);
+    expect(resolved.ok).toBe(false);
+    if (!resolved.ok) expect(resolved.reason).toBe("never_grantable");
+  });
+
+  it.each([
+    "loki:3100",
+    "ftp://loki:3100",
+    "http://user:pw@loki:3100",
+    "http://loki:3100?token=abc",
+  ])("refuses the malformed endpoint %s", (endpoint) => {
+    const resolved = resolveLokiPushTarget(endpoint);
+    expect(resolved.ok).toBe(false);
+    if (!resolved.ok) {
+      expect(resolved.reason).toBe("invalid_endpoint");
+      expect(resolved.shown).not.toContain("pw");
+      expect(resolved.shown).not.toContain("abc");
+    }
+  });
+});
+
+describe("flushLokiBuffer — dial path", () => {
+  it("dials a private endpoint as an operator-approved origin, not through the public pin", async () => {
+    configure("http://10.0.0.5:3100/loki/api/v1/push");
+    safeFetchMock.mockResolvedValue(new Response(null, { status: 204 }));
+    buffer(2);
+
+    await flushLokiBuffer();
+
+    expect(safeFetchMock).toHaveBeenCalledTimes(1);
+    const [url, init, opts] = safeFetchMock.mock.calls[0];
+    expect(url).toBe("http://10.0.0.5:3100/loki/api/v1/push");
+    expect(init.headers.Authorization).toBe(`Basic ${BASIC}`);
+    expect(opts.operatorApprovedPrivateOrigin).toBe("http://10.0.0.5:3100");
+    expect(opts.requirePublicHost).toBeUndefined();
+    expect(JSON.parse(init.body).streams[0].values).toHaveLength(2);
+    expect(stderrLines).toEqual([]);
+  });
+
+  it("never dials a metadata endpoint and says why", async () => {
+    configure("http://169.254.169.254:3100");
+    buffer(3);
+
+    await flushLokiBuffer();
+
+    expect(safeFetchMock).not.toHaveBeenCalled();
+    expect(stderrLines).toHaveLength(1);
+    expect(stderrLines[0]).toContain("never_grantable");
+    expect(stderrLines[0]).toContain("3 events dropped");
+  });
+});
+
+describe("flushLokiBuffer — failures reach stderr, once per window", () => {
+  it("reports a non-2xx answer with origin, status and dropped count", async () => {
+    configure("https://logs.example.com/loki/api/v1/push/loki/api/v1/push");
+    safeFetchMock.mockResolvedValue(
+      new Response("404 page not found", { status: 404 }),
+    );
+    buffer(4);
+
+    await flushLokiBuffer();
+
+    expect(stderrLines).toHaveLength(1);
+    expect(stderrLines[0]).toContain("https://logs.example.com");
+    expect(stderrLines[0]).toContain("HTTP 404");
+    expect(stderrLines[0]).toContain("4 events dropped");
+  });
+
+  it("reports a thrown error by class and socket code, never by message", async () => {
+    configure("http://loki.lan:3100");
+    const cause = Object.assign(new Error("connect ECONNREFUSED"), {
+      code: "ECONNREFUSED",
+    });
+    safeFetchMock.mockRejectedValue(
+      new SafeFetchError(
+        `safeFetch network error: http://${USERNAME}:${PASSWORD}@loki.lan`,
+        "network",
+        { cause },
+      ),
+    );
+    buffer(1);
+
+    await flushLokiBuffer();
+
+    expect(stderrLines).toHaveLength(1);
+    expect(stderrLines[0]).toContain("http://loki.lan:3100");
+    expect(stderrLines[0]).toContain("network ECONNREFUSED");
+    expect(stderrLines[0]).toContain("1 event dropped");
+  });
+
+  it("writes one line per reason per window and carries the suppressed count forward", async () => {
+    vi.useFakeTimers({ toFake: ["Date"] });
+    configure("http://loki.lan:3100");
+    safeFetchMock.mockImplementation(
+      async () => new Response(null, { status: 503 }),
+    );
+
+    for (let i = 0; i < 5; i++) {
+      buffer(2);
+      await flushLokiBuffer();
+      vi.advanceTimersByTime(5_000);
+    }
+    expect(stderrLines).toHaveLength(1);
+    expect(stderrLines[0]).toContain("2 events dropped");
+
+    // A different reason is not muted by the first one's window.
+    safeFetchMock.mockImplementationOnce(
+      async () => new Response(null, { status: 401 }),
+    );
+    buffer(1);
+    await flushLokiBuffer();
+    expect(stderrLines).toHaveLength(2);
+    expect(stderrLines[1]).toContain("HTTP 401");
+
+    vi.advanceTimersByTime(LOKI_FAILURE_NOTICE_INTERVAL_MS);
+    buffer(2);
+    await flushLokiBuffer();
+    expect(stderrLines).toHaveLength(3);
+    expect(stderrLines[2]).toContain("HTTP 503");
+    // Four suppressed batches of two plus this batch of two.
+    expect(stderrLines[2]).toContain("10 events dropped");
+  });
+
+  it("never prints the credentials or the basic-auth header", async () => {
+    configure("http://loki.lan:3100");
+    safeFetchMock.mockResolvedValueOnce(new Response(null, { status: 403 }));
+    safeFetchMock.mockRejectedValueOnce(
+      new SafeFetchError(`failed with Basic ${BASIC} ${PASSWORD}`, "timeout"),
+    );
+    buffer(1);
+    await flushLokiBuffer();
+    buffer(1);
+    await flushLokiBuffer();
+
+    expect(stderrLines).toHaveLength(2);
+    const all = stderrLines.join("");
+    expect(all).not.toContain(PASSWORD);
+    expect(all).not.toContain(USERNAME);
+    expect(all).not.toContain(BASIC);
+  });
+
+  it("stays silent on success", async () => {
+    configure("http://loki.lan:3100");
+    safeFetchMock.mockResolvedValue(new Response(null, { status: 204 }));
+    buffer(1);
+    await flushLokiBuffer();
+    expect(stderrLines).toEqual([]);
+  });
+
+  it("does not feed its own notice back into the Loki buffer", async () => {
+    configure("http://loki.lan:3100");
+    safeFetchMock.mockResolvedValue(new Response(null, { status: 500 }));
+    buffer(1);
+    await flushLokiBuffer();
+    expect(stderrLines).toHaveLength(1);
+
+    // Nothing was buffered by the failure, so the next flush has nothing
+    // to send.
+    safeFetchMock.mockClear();
+    await flushLokiBuffer();
+    expect(safeFetchMock).not.toHaveBeenCalled();
+  });
+});
+
+describe("flushLokiBuffer — real dial to a loopback Loki", () => {
+  let server: Server;
+  let received: Array<{ url: string; auth: string | undefined }>;
+  let status: number;
+
+  beforeEach(async () => {
+    useRealSafeFetch.value = true;
+    received = [];
+    status = 204;
+    server = createServer((req, res) => {
+      received.push({ url: req.url ?? "", auth: req.headers.authorization });
+      req.resume();
+      req.on("end", () => {
+        res.statusCode = status;
+        res.end();
+      });
+    });
+    await new Promise<void>((resolve) =>
+      server.listen(0, "127.0.0.1", resolve),
+    );
+  });
+
+  afterEach(async () => {
+    await new Promise<void>((resolve) => server.close(() => resolve()));
+  });
+
+  function endpoint(path = ""): string {
+    const { port } = server.address() as AddressInfo;
+    return `http://127.0.0.1:${port}${path}`;
+  }
+
+  it("delivers to a non-public address given as the full push URL", async () => {
+    configure(endpoint("/loki/api/v1/push"));
+    buffer(1);
+
+    await flushLokiBuffer();
+
+    expect(received).toEqual([
+      { url: "/loki/api/v1/push", auth: `Basic ${BASIC}` },
+    ]);
+    expect(stderrLines).toEqual([]);
+  });
+
+  it("reports the 404 a wrong path produces instead of swallowing it", async () => {
+    status = 404;
+    configure(endpoint("/wrong"));
+    buffer(2);
+
+    await flushLokiBuffer();
+
+    expect(received).toHaveLength(1);
+    expect(received[0].url).toBe("/wrong/loki/api/v1/push");
+    expect(stderrLines).toHaveLength(1);
+    expect(stderrLines[0]).toContain(`${endpoint()} failed (HTTP 404)`);
+  });
+});
diff --git a/src/lib/logging/transports.ts b/src/lib/logging/transports.ts
index 4bbddb090..0e1b4cb02 100644
--- a/src/lib/logging/transports.ts
+++ b/src/lib/logging/transports.ts
@@ -2,7 +2,8 @@ import type { WideEvent } from "./types";
 import { getLoggingConfig } from "./config";
 import { shouldEmit } from "./sampler";
 import { appendLogEvent } from "./in-memory-buffer";
-import { safeFetch } from "@/lib/safe-fetch";
+import { safeFetch, SafeFetchError } from "@/lib/safe-fetch";
+import { canonicalOrigin } from "@/lib/private-origin-policy";
 
 /** Event auf stdout als einzelne JSON-Zeile schreiben */
 function emitToStdout(event: WideEvent): void {
@@ -31,7 +32,133 @@ function initLokiTransport(): void {
   if (lokiFlushTimer.unref) lokiFlushTimer.unref();
 }
 
-async function flushLokiBuffer(): Promise<void> {
+const LOKI_PUSH_PATH = "/loki/api/v1/push";
+const LOKI_PUSH_TIMEOUT_MS = 10_000;
+
+export interface LokiPushTarget {
+  /** The URL the batch is POSTed to. */
+  url: string;
+  /**
+   * The exact origin handed to `safeFetch` as the operator approval. Also the
+   * only part of the endpoint that ever appears in a failure line: it carries
+   * no userinfo, path or query by construction.
+   */
+  origin: string;
+}
+
+export type LokiTargetResolution =
+  | { ok: true; target: LokiPushTarget }
+  | {
+      ok: false;
+      reason: "invalid_endpoint" | "never_grantable";
+      shown: string;
+    };
+
+/**
+ * Turn `LOKI_ENDPOINT` into the push URL and the origin it may dial.
+ *
+ * Both spellings an operator reaches for work: the base URL
+ * (`http://loki:3100`, the push path is appended) and the full push URL
+ * (`http://loki:3100/loki/api/v1/push`, used as is, trailing slash or not).
+ * Appending unconditionally turned the second form into
+ * `/loki/api/v1/push/loki/api/v1/push` and a 404.
+ *
+ * Why the endpoint dials as an operator-approved origin rather than through
+ * the public-host pin: `LOKI_ENDPOINT` is read from the server environment in
+ * `config.ts` and nowhere else. No request field, settings row or admin form
+ * can set it, so there is no user-supplied host to defend against, and the
+ * public-only pin was refusing the common deployment (a Loki on the same LAN
+ * or Docker network) without a word. The exact origin still goes through the
+ * pinned operator resolver in `safeFetch` with redirects forbidden, and the
+ * never-grantable floor holds: an endpoint whose literal host is the
+ * unspecified address, link-local or the metadata range is refused here
+ * (`canonicalOrigin`), and a name that resolves there is dropped at dial time.
+ */
+export function resolveLokiPushTarget(endpoint: string): LokiTargetResolution {
+  let url: URL;
+  try {
+    url = new URL(endpoint.trim());
+  } catch {
+    return { ok: false, reason: "invalid_endpoint", shown: "(unparseable)" };
+  }
+  if (url.protocol !== "http:" && url.protocol !== "https:") {
+    return { ok: false, reason: "invalid_endpoint", shown: url.protocol };
+  }
+  // `url.origin` never carries userinfo, so it is safe to print even when
+  // the endpoint itself is refused for carrying credentials.
+  if (url.username || url.password || url.search || url.hash) {
+    return { ok: false, reason: "invalid_endpoint", shown: url.origin };
+  }
+  const origin = canonicalOrigin(url.origin);
+  if (!origin) {
+    return { ok: false, reason: "never_grantable", shown: url.origin };
+  }
+  const basePath = url.pathname.replace(/\/+$/, "");
+  const pushPath = basePath.endsWith(LOKI_PUSH_PATH)
+    ? basePath
+    : `${basePath}${LOKI_PUSH_PATH}`;
+  return { ok: true, target: { url: `${origin}${pushPath}`, origin } };
+}
+
+/**
+ * Failure notices for the Loki push, written straight to stderr.
+ *
+ * Never through `emitEvent`: a failing Loki push that reported itself as a
+ * wide event would buffer that event for the same failing push. At most one
+ * line per reason per window, so a Loki that is down for an hour costs twelve
+ * lines, not seven hundred. Events dropped while a reason is quiet are counted
+ * and reported on its next line, so the numbers add up.
+ */
+export const LOKI_FAILURE_NOTICE_INTERVAL_MS = 5 * 60 * 1000;
+const lokiFailureNotices = new Map<
+  string,
+  { lastAt: number; droppedSinceLast: number }
+>();
+
+function reportLokiFailure(
+  shownEndpoint: string,
+  reason: string,
+  droppedEvents: number,
+): void {
+  const now = Date.now();
+  const entry = lokiFailureNotices.get(reason);
+  if (entry && now - entry.lastAt < LOKI_FAILURE_NOTICE_INTERVAL_MS) {
+    entry.droppedSinceLast += droppedEvents;
+    return;
+  }
+  const dropped = droppedEvents + (entry?.droppedSinceLast ?? 0);
+  lokiFailureNotices.set(reason, { lastAt: now, droppedSinceLast: 0 });
+  process.stderr.write(
+    `[logging] Loki push to ${shownEndpoint} failed (${reason}); ` +
+      `${dropped} event${dropped === 1 ? "" : "s"} dropped. ` +
+      `Repeats of this failure are reported at most every 5 minutes.\n`,
+  );
+}
+
+/**
+ * The failure reason as a short class, never the error message: messages
+ * from the fetch stack can embed the target URL, and this line goes to stderr
+ * unredacted. A socket error code (`ECONNREFUSED`, `ENOTFOUND`) is kept
+ * because it is the part that tells an operator what to fix.
+ */
+function classifyLokiError(err: unknown): string {
+  const kind = err instanceof SafeFetchError ? err.kind : "error";
+  let cause: unknown = err instanceof SafeFetchError ? err.cause : err;
+  for (
+    let depth = 0;
+    depth < 4 && cause && typeof cause === "object";
+    depth++
+  ) {
+    const code = (cause as { code?: unknown }).code;
+    if (typeof code === "string" && /^[A-Z][A-Z0-9_]{1,40}$/.test(code)) {
+      return `${kind} ${code}`;
+    }
+    cause = (cause as { cause?: unknown }).cause;
+  }
+  return kind;
+}
+
+export async function flushLokiBuffer(): Promise<void> {
   if (lokiBuffer.length === 0) return;
   const config = getLoggingConfig();
   if (!config.lokiEndpoint) return;
@@ -39,6 +166,13 @@ async function flushLokiBuffer(): Promise<void> {
   const batch = lokiBuffer;
   lokiBuffer = [];
 
+  const resolved = resolveLokiPushTarget(config.lokiEndpoint);
+  if (!resolved.ok) {
+    reportLokiFailure(resolved.shown, resolved.reason, batch.length);
+    return;
+  }
+  const { target } = resolved;
+
   const streams = [
     {
       stream: {
@@ -64,21 +198,41 @@ async function flushLokiBuffer(): Promise<void> {
       );
   }
 
+  let res: Response;
   try {
-    await safeFetch(
-      `${config.lokiEndpoint}/loki/api/v1/push`,
+    res = await safeFetch(
+      target.url,
       {
         method: "POST",
         headers,
         body: JSON.stringify({ streams }),
       },
-      // Operator-configured Loki endpoint — pin the connect-time IP
-      // against DNS rebinding.
-      { timeoutMs: 10_000, requirePublicHost: true },
+      // Operator-configured endpoint: dial exactly its origin through the
+      // pinned operator resolver (see `resolveLokiPushTarget`).
+      {
+        timeoutMs: LOKI_PUSH_TIMEOUT_MS,
+        operatorApprovedPrivateOrigin: target.origin,
+      },
     );
-  } catch {
-    // Events gehen verloren — akzeptabel fuer Logging
+  } catch (err) {
+    // The batch is already detached from the buffer; say so rather than
+    // losing it without a trace.
+    reportLokiFailure(target.origin, classifyLokiError(err), batch.length);
+    return;
   }
+
+  // Loki answers 204. Anything else, including a 3xx the forbidden redirect
+  // left unfollowed, means the batch did not land.
+  if (!res.ok) {
+    reportLokiFailure(target.origin, `HTTP ${res.status}`, batch.length);
+  }
+  await res.body?.cancel().catch(() => {});
+}
+
+/** Test helper: clear the buffer and the failure-notice windows. */
+export function _resetLokiTransportForTests(): void {
+  lokiBuffer = [];
+  lokiFailureNotices.clear();
 }
 
 /**
diff --git a/src/proxy.ts b/src/proxy.ts
index 23c1e0cf7..7eea0ed35 100644
--- a/src/proxy.ts
+++ b/src/proxy.ts
@@ -244,6 +244,26 @@ const LEGACY_ADMIN_ANCHORS: Record<string, string> = {
   "/admin/section-danger-zone": "/admin/danger-zone",
 };
 
+/**
+ * Presence marker on every HealthLog page response, read by `public/sw.js`.
+ *
+ * The service worker is registered with scope `/` and serves `/_next/static/*`
+ * cache-first. When HealthLog is stopped and a different app starts on the
+ * same origin (`localhost:3000` on a developer machine is the usual case), the
+ * worker went on serving HealthLog's cached chunks to that app (#847). It
+ * needs a way to tell a HealthLog page from someone else's, and nothing
+ * HealthLog already sends is specific enough: `x-request-id`, the nonce CSP
+ * and the COOP/COEP set are headers any Next.js app may emit. So the proxy
+ * adds one of its own.
+ *
+ * Presence only, value `1`: no version and no build id, because a version on
+ * every page is a free fingerprint for anyone scanning for an outdated
+ * instance and the worker does not need it. Pages only, not `/api/*`: the
+ * worker checks navigations and nothing else. Keep the name in lockstep with
+ * `HEALTHLOG_PAGE_MARKER_HEADER` in `public/sw.js`.
+ */
+export const HEALTHLOG_PAGE_MARKER_HEADER = "X-HealthLog-Page";
+
 function generateNonce(): string {
   const bytes = crypto.getRandomValues(new Uint8Array(16));
   let binary = "";
@@ -484,6 +504,10 @@ export function proxy(request: NextRequest) {
   // Request ID for log correlation
   response.headers.set("x-request-id", requestId);
 
+  if (!isApiRoute) {
+    response.headers.set(HEALTHLOG_PAGE_MARKER_HEADER, "1");
+  }
+
   // The document vault's decrypt-and-serve route is framed SAME-ORIGIN by
   // the document detail preview (an <iframe> for inline-class PDFs). The
   // blanket `X-Frame-Options: DENY` + `frame-ancestors 'none'` below would