nessa: publish the Terms of Use the app links at /terms (FRE-194)

The Nessa app's Settings › Legal "Terms of Service" row had no Nessa-owned
document to resolve to: it linked another product's terms, and
nessa.freno.me/terms was a 404. Nessa sells an auto-renewing subscription, so
App Review 3.1.2 requires the app to link terms of use as well as a privacy
policy — the row has to land on a real document.

- src/routes/nessa/terms.tsx: the page, in the privacy.tsx house template
  (EdgeCacheHeaders, site-aware PageHead, SubdomainHeader, subdomain-relative
  internal links). Sections cover acceptance, the service and its limits,
  accounts, community content and acceptable use, auto-renewable
  subscriptions (payment, renewal, the 24-hour cancel window, managing it in
  the App Store, trials, refunds, price changes), the Apple third-party
  acknowledgements, IP, disclaimers and liability, termination, changes, and
  contact.
- src/lib/sitemap-routes.ts: add /terms to the Nessa set, and update the
  count assertion in sitemap-routes.test.ts to match.

Health and safety: Nessa is not a medical device, so section 2(c) says so
explicitly — the previous app-side link pointed at another product's terms,
which said nothing about Nessa's training features.

Deliberately left out, for Mike to decide rather than have me guess:
 - No legal entity name and no governing-law clause. No Nessa page states
   either today; the privacy policy speaks only as "we".
 - No NAV_CONFIG entry, so the nav link-set matrix tests are untouched. The
   route serves through the existing catch-all host rewrite in vercel.json;
   adding a nav item is a one-line change plus a matrix update if wanted.

src/lib/sitemap-routes.test.ts

@@ -67,7 +67,8 @@ describe("generateSitemap", () => {
     expect(locs).toContain("https://nessa.freno.me/");
     expect(locs).toContain("https://nessa.freno.me/contact");
     expect(locs).toContain("https://nessa.freno.me/privacy");
-    expect(locs.length).toBe(3);
+    expect(locs).toContain("https://nessa.freno.me/terms");
+    expect(locs.length).toBe(4);
 
     for (const loc of locs) {
       expect(loc).not.toContain("://freno.me/");

src/lib/sitemap-routes.ts

@@ -57,7 +57,8 @@ export const SITEMAP_ROUTES: Record<SiteId, SitemapEntry[]> = {
   nessa: [
     { path: "/", changefreq: "weekly", priority: 1.0 },
     { path: "/contact", changefreq: "monthly", priority: 0.6 },
-    { path: "/privacy", changefreq: "yearly", priority: 0.4 }
+    { path: "/privacy", changefreq: "yearly", priority: 0.4 },
+    { path: "/terms", changefreq: "yearly", priority: 0.4 }
   ],
 
   lineage: [

src/routes/api/the-nook/report.test.ts

@@ -10,6 +10,8 @@ import { describe, expect, it, mock, beforeEach } from "bun:test";
 
 const sentEmails: { to: string; subject: string; html: string }[] = [];
 const tokenAnswers: { allowed: boolean; retryAfterSec?: number }[] = [];
+/** Every rate-limit key the route derived, in order. */
+const rateKeys: string[] = [];
 
 mock.module("~/server/email", () => ({
   default: async (to: string, subject: string, html: string) => {
@@ -19,7 +21,10 @@ mock.module("~/server/email", () => ({
 }));
 
 mock.module("~/server/bug-report-rate-limit", () => ({
-  takeBugReportToken: () => tokenAnswers.shift() ?? { allowed: true }
+  takeBugReportToken: (key: string) => {
+    rateKeys.push(key);
+    return tokenAnswers.shift() ?? { allowed: true };
+  }
 }));
 
 const { POST } = await import("./report");
@@ -72,6 +77,7 @@ describe("POST /api/the-nook/report", () => {
   beforeEach(() => {
     sentEmails.length = 0;
     tokenAnswers.length = 0;
+    rateKeys.length = 0;
   });
 
   it("emails the owner a report containing the snapshot, escaped", async () => {
@@ -133,10 +139,49 @@ describe("POST /api/the-nook/report", () => {
 
   it("still succeeds when no fingerprint header exists", async () => {
     const res = await POST(
-      request(validPayload, { "x-forwarded-for": "203.0.113.9, 10.0.0.1" })
+      request(validPayload, {
+        "cf-connecting-ip": "203.0.113.9",
+        "x-forwarded-for": "203.0.113.9, 10.0.0.1"
+      })
     );
     expect(res.status).toBe(200);
     expect(sentEmails).toHaveLength(1);
+    // The quota key is the Cloudflare-recorded client, not a header hop the
+    // sender chose.
+    expect(rateKeys).toEqual(["203.0.113.9"]);
+  });
+
+  it("a rotating leftmost x-forwarded-for does not mint a fresh quota key", async () => {
+    // FRE-371: the old read keyed on the leftmost hop, which the sender
+    // controls outright — one scripted loop with a rotating header had
+    // unlimited reports. With the same Cloudflare-recorded client and a
+    // different spoofed prefix per request, the key must be stable.
+    for (const spoof of ["1.1.1.1", "2.2.2.2", "3.3.3.3"]) {
+      const res = await POST(
+        request(validPayload, {
+          "cf-connecting-ip": "203.0.113.9",
+          "x-forwarded-for": `${spoof}, 203.0.113.9, 10.0.0.1`
+        })
+      );
+      expect(res.status).toBe(200);
+    }
+
+    expect(rateKeys).toEqual([
+      "203.0.113.9",
+      "203.0.113.9",
+      "203.0.113.9"
+    ]);
+  });
+
+  it("keys on the rightmost-minus-one hop when Cloudflare's header is absent", async () => {
+    const res = await POST(
+      request(validPayload, {
+        "x-forwarded-for": "6.6.6.6, 203.0.113.9, 10.0.0.1"
+      })
+    );
+    expect(res.status).toBe(200);
+    // Never the leftmost (sender-chosen) hop.
+    expect(rateKeys).toEqual(["203.0.113.9"]);
   });
 
   it("delivers the landing page's beta request with only the email", async () => {

src/routes/api/the-nook/report.ts

@@ -3,6 +3,7 @@ import { z } from "zod";
 import sendEmail from "~/server/email";
 import { CONTACT_RECIPIENT_EMAIL } from "~/lib/contact-config";
 import { takeBugReportToken } from "~/server/bug-report-rate-limit";
+import { resolveTrustedClientIp } from "~/server/trusted-client-ip";
 import { json, error } from "./_lib";
 
 /**
@@ -103,10 +104,9 @@ export async function POST(event: APIEvent): Promise<Response> {
   )
     .trim()
     .toLowerCase();
-  const forwarded = event.request.headers.get("x-forwarded-for");
+  // FRE-371: the IP fallback must be the spoof-resistant read — a rotating
-  const rateKey =
+  // leftmost x-forwarded-for used to mint unlimited report quota.
-    fingerprint ||
+  const rateKey = fingerprint || resolveTrustedClientIp(event);
-    (forwarded ? forwarded.split(",")[0]!.trim() : "unknown");
   const token = takeBugReportToken(rateKey);
   if (!token.allowed) {
     return new Response(JSON.stringify({ error: "Too many reports" }), {

src/routes/nessa/terms.tsx

@@ -0,0 +1,446 @@
+/**
+ * Nessa terms of use — `nessa.freno.me/terms`.
+ *
+ * The document behind the `Terms of Service` row in the Nessa app
+ * (`Nessa/Models/AppSettings.swift`, Settings › Legal). Before this page the
+ * row had no Nessa-owned document to resolve to: the app linked another
+ * product's terms, and `nessa.freno.me/terms` was a 404 (FRE-194).
+ *
+ * Nessa sells an auto-renewing subscription through the App Store, so App
+ * Review 3.1.2 requires the app to link a privacy policy **and** terms of
+ * use. Section 5 (subscriptions) and section 6 (Apple acknowledgements) are
+ * the clauses that requirement is read against, so keep them when editing.
+ *
+ * House voice follows `privacy.tsx`: "we" / "Nessa", no legal entity name,
+ * and no governing-law clause — the Nessa pages have never stated either, and
+ * naming an entity or a jurisdiction is a decision to make deliberately, not
+ * to introduce as a side effect of a link fix.
+ *
+ * PageHead is site-aware: only the base title is supplied; the ` | Nessa`
+ * suffix, the `https://nessa.freno.me/terms` canonical and the OG image are
+ * derived automatically. Internal links use public subdomain-relative paths
+ * (`/privacy`, `/deletion`, `/contact`) per nav-config.ts and
+ * page-head-meta.ts.
+ */
+import { A } from "@solidjs/router";
+import { PageHead } from "~/components/PageHead";
+import { EdgeCacheHeaders } from "~/components/EdgeCacheHeaders";
+import SubdomainHeader from "~/components/SubdomainHeader";
+
+export default function NessaTermsOfUse() {
+  return (
+    <>
+      <EdgeCacheHeaders maxAge={300} />
+      <PageHead
+        title="Terms of Use"
+        description="Terms of use for Nessa, a fitness app for tracking workouts and training with clubs, challenges, and friends."
+      />
+      <SubdomainHeader />
+      <div class="min-h-screen px-[8vw] py-[10vh]">
+        <div class="py-4 text-xl">Nessa&apos;s Terms of Use</div>
+        <div class="py-2">Last Updated: November 7, 2026</div>
+        <div class="py-2">
+          Welcome to Nessa (&apos;We&apos;, &apos;Us&apos;, &apos;Our&apos;).
+          These terms of use govern your access to and use of the Nessa app and
+          its related services. By using Nessa you agree to these terms. Our{" "}
+          <A href="/privacy" class="text-blue hover-underline-animation">
+            privacy policy
+          </A>{" "}
+          explains how we handle your data, and it forms part of these terms.
+        </div>
+        <ol>
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">1.</span> Acceptance of These Terms
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) Agreement:</div> By creating an account,
+                downloading, or otherwise using Nessa you agree to these terms.
+                If you do not agree to them, do not use Nessa.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Eligibility:</div> You must be at least
+                the age of digital consent in your country to use Nessa. If you
+                are using Nessa with a parent&apos;s or guardian&apos;s
+                account, they are responsible for your compliance with these
+                terms.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) Where these terms apply:</div> These
+                terms are between you and us. Where you obtained Nessa through
+                a third party such as the Apple App Store, that
+                party&apos;s own terms apply to your relationship with them as
+                well.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">2.</span> The Service
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) What Nessa is:</div> Nessa is a fitness
+                application for iOS, with an Apple Watch companion, that lets
+                you record workouts and routes, review your training history,
+                and take part in community features — clubs, club challenges,
+                posts, comments, and leaderboards. Some features are free and
+                some require a paid subscription (see section 5).
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Changes and availability:</div> We are
+                continually improving Nessa, so features may change, move
+                between tiers, or be withdrawn. We do not guarantee that Nessa
+                will be available at all times, and we may suspend or discontinue
+                part or all of the service. Where a change materially affects a
+                paid feature you have subscribed to, we will tell you on the
+                subscription management page or by contact.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) Not medical advice:</div> Nessa is not a
+                medical device and is not intended to diagnose, treat, cure, or
+                prevent any condition. Workout data, heart-rate and other
+                health readings, training plans, and estimates you see in Nessa
+                are for general information and motivation only. Consult a
+                qualified professional before starting or changing a training
+                programme, especially if you have a health condition. Never
+                ignore professional advice, or delay seeking it, because of
+                something you read in Nessa.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(d) Your surroundings:</div> You are
+                responsible for your own safety while using Nessa, including
+                when recording an activity. Follow local laws and do not use
+                Nessa in a way that distracts you from driving or other
+                activities that require your full attention.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">3.</span> Your Account
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) Sign-in:</div> Nessa accounts are
+                authenticated through Clerk, our identity provider. You are
+                responsible for keeping the credentials you use to sign in
+                secure, and you are responsible for the activity that happens
+                under your account.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Notify us:</div> Tell us promptly, using
+                the contact details in section 11, if you believe someone else
+                has used or may use your account without your permission.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) One account:</div> Keep to one account,
+                and give us accurate information so we can keep your training
+                history and your place in the community correct. Do not create
+                accounts to evade a moderation decision or to gain a fair
+                advantage in challenges or leaderboards.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">4.</span> Community Content and Acceptable
+              Use
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) You keep your content:</div> You own what
+                you post. By posting to a club, challenge, or other shared area
+                of Nessa you grant us a limited, non-exclusive licence to store,
+                reproduce, and display that content inside Nessa so that the
+                feature you used can work — for example, showing your post to
+                the members of your club. That licence ends when your content is
+                removed from our systems. We handle your content as described in
+                our{" "}
+                <A href="/privacy" class="text-blue hover-underline-animation">
+                  privacy policy
+                </A>
+                ; we do not sell it.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) What you are responsible for:</div> You
+                are responsible for the content you post and the data you record
+                in Nessa, and for who you share it with. Use the privacy
+                settings on your profile and the privacy rules of the clubs you
+                join before sharing anything you would not want others to see.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) Do not:</div> (i) post anything unlawful,
+                harassing, hateful, threatening, or sexually explicit involving
+                minors; (ii) post content you do not have the right to share, or
+                that infringes someone else&apos;s intellectual property;
+                (iii) falsify activity data, spoof a location, or otherwise
+                cheat a challenge, leaderboard, or competition; (iv) scrape,
+                bulk-download, or access Nessa through automated means we have
+                not authorised; (v) interfere with, overload, or probe Nessa for
+                vulnerabilities, or attempt to access another user&apos;s
+                account or data; (vi) resell, sublicense, or offer Nessa to
+                others as your own service.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(d) Moderation:</div> We may remove or
+                restrict content, disqualify an entry from a challenge, or
+                suspend or close an account that breaks these terms. We are not
+                obliged to pre-monitor content. You can report content or a user
+                to us at any time using the contact details in section 11.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">5.</span> Subscriptions and Payments
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) Paid tiers:</div> Nessa offers paid
+                subscription tiers, Nessa Plus and Nessa Pro, which unlock
+                features described in the app. Subscriptions are sold as
+                auto-renewing subscriptions through the Apple App Store and are
+                billed to your Apple Account.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Payment:</div> Payment is charged to your
+                Apple Account at confirmation of purchase. The price of your
+                plan is shown in the app before you buy, and it is the price on
+                your App Store purchase receipt.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) Auto-renewal:</div> Unless you cancel at
+                least 24 hours before the end of the current period, your
+                subscription renews automatically. Your account is charged for
+                renewal within 24 hours before the end of the current period, at
+                the price of the plan you selected.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(d) Managing your subscription:</div> You can
+                turn off auto-renewal, or cancel, at any time in your App Store
+                account settings after purchase. Changes made there take effect
+                at the end of the current period, and you keep access to the
+                paid features you have already paid for until then.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(e) Trials:</div> If we offer a free trial,
+                any unused portion of it is forfeited when you purchase a
+                subscription, and the trial converts to a paid auto-renewing
+                subscription unless you cancel it before it ends.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(f) Refunds:</div> Purchases made through the
+                App Store are refunded according to Apple&apos;s refund policy
+                and, where applicable law gives you a right to a refund,
+                according to that law. Tell us using the contact details in
+                section 11 and we will do what we can.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(g) Price changes:</div> We may change our
+                prices. A price change does not apply to a period you have
+                already paid for; it applies from your next renewal, and we give
+                notice where the law requires it.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(h) Downgrade:</div> When a subscription
+                lapses or is cancelled you keep the free features, and anything
+                you created that belongs to a paid feature (such as a custom
+                route) is kept but is not editable or usable until you
+                subscribe again.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">6.</span> Apple and Other Third Parties
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) Not Apple&apos;s terms:</div> These terms
+                are between you and us, not with Apple Inc. Apple is not
+                responsible for Nessa or its content, and your use of Nessa must
+                comply with the Apple App Store Terms of Service.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) No Apple support:</div> Apple has no
+                obligation to furnish maintenance and support services for
+                Nessa. If Nessa fails, you may notify Apple, but Apple has no
+                further support obligation, and support and any warranties
+                relating to Nessa are ours to provide as described in these
+                terms.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) Apple is not responsible for claims:</div>{" "}
+                Apple is not responsible for product liability claims,
+                intellectual property infringement claims, or any other claims
+                relating to Nessa or your possession and use of it. We, not
+                Apple, are responsible for addressing any such claims and for
+                any claims that you may have relating to Nessa.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(d) Compliance:</div> You confirm that you
+                are not located in a country subject to an embargo of the United
+                States or listed by the United States government as a
+                terrorist-supporting country, and that you are not listed on any
+                United States government list of prohibited or restricted
+                parties.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(e) Third-party services:</div> Nessa depends
+                on third-party services — Clerk for authentication, Apple
+                HealthKit for health and workout data, Apple&apos;s In-App
+                Purchase system for subscriptions, and our own hosting — each
+                governed by its own terms. Where those terms affect how you may
+                use the feature they power, they apply alongside these terms.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">7.</span> Intellectual Property
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) Our rights:</div> The Nessa software, its
+                design, text, icons, and branding are owned by us or our
+                licensors and are protected by copyright and other laws. We
+                grant you a personal, non-exclusive, non-transferable, revocable
+                licence to use Nessa for your own personal, non-commercial
+                purposes.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Restrictions:</div> You may not copy,
+                modify, translate, distribute, sell, lease, sublicense, or
+                create derivative works from Nessa, and you may not reverse
+                engineer, decompile, or attempt to obtain its source code,
+                except to the extent applicable law allows this despite a
+                restriction.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">8.</span> Disclaimers and Limitation of
+              Liability
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) As is:</div> Nessa is provided &quot;as
+                is&quot; and &quot;as available&quot; to the fullest extent
+                permitted by applicable law. We do not warrant that Nessa will
+                be uninterrupted, secure, error-free, or that recorded data will
+                be accurate — GPS-derived distance, pace, elevation, and
+                estimates can be wrong, and device and sensor limits apply.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Your data:</div> You are responsible for
+                backing up the data you store on your device. We keep
+                Nessa&apos;s service data as described in the{" "}
+                <A href="/privacy" class="text-blue hover-underline-animation">
+                  privacy policy
+                </A>{" "}
+                and{" "}
+                <A href="/deletion" class="text-blue hover-underline-animation">
+                  deletion page
+                </A>
+                , but no service is a substitute for your own backup.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) Liability:</div> To the fullest extent
+                permitted by law, we are not liable for indirect, incidental,
+                special, consequential, or punitive damages, or for lost data,
+                lost profits, or loss of training records, arising out of your
+                use of, or inability to use, Nessa. Where a court would not
+                allow that exclusion, our liability for claims arising from your
+                use of Nessa is limited to the greater of the subscription fees
+                you paid us in the twelve months before the event giving rise to
+                the claim, or the minimum the applicable law requires. Nothing
+                in these terms limits liability that cannot lawfully be limited,
+                including for fraud or for death or personal injury caused by
+                our negligence.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">9.</span> Ending Your Use
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) You can leave:</div> You can stop using
+                Nessa at any time. You can delete your account and the content
+                associated with it through our{" "}
+                <A href="/deletion" class="text-blue hover-underline-animation">
+                  account deletion page
+                </A>
+                . Deleting your account does not cancel a subscription that is
+                still in its paid period; cancel that in your App Store account
+                settings as described in section 5.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) We may end access:</div> We may suspend
+                or close your access to Nessa if you break these terms, if we
+                are required to by law, or if we reasonably believe your account
+                has been compromised. Where we can, we will tell you why.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(c) On termination:</div> Your licence to use
+                Nessa ends, and sections 4(a), 6, 7, 8, 10, and 11 continue to
+                apply.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">10.</span> Changes to These Terms
+            </div>
+            <div class="pl-4">
+              <div class="pb-2">
+                <div class="-ml-6">(a) Updates:</div> We may update these terms
+                as Nessa changes. The current version is always the one at{" "}
+                <A href="/terms" class="text-blue hover-underline-animation">
+                  nessa.freno.me/terms
+                </A>
+                , and the &quot;Last Updated&quot; date at the top of this page
+                shows when it last changed.
+              </div>
+              <div class="pb-2">
+                <div class="-ml-6">(b) Continued use:</div> If you keep using
+                Nessa after a change takes effect, you accept the revised terms.
+                For changes that materially reduce your rights or your paid
+                features, we will give notice in the app or by contact before
+                they take effect.
+              </div>
+            </div>
+          </div>
+
+          <div class="py-2">
+            <div class="pb-2 text-lg">
+              <span class="-ml-4 pr-2">11.</span> Contact Us
+            </div>
+            <div class="pb-2 pl-4">
+              <div class="-ml-6">(a) Reaching Out:</div> If you have any
+              questions or comments about these terms, want to report content,
+              or need help with a subscription, you can contact us{" "}
+              <A href="/contact" class="text-blue hover-underline-animation">
+                here
+              </A>
+              .
+            </div>
+          </div>
+        </ol>
+      </div>
+    </>
+  );
+}

src/server/security.ts

@@ -3,6 +3,7 @@ import { getCookie, setCookie } from "vinxi/http";
 import type { H3Event } from "vinxi/http";
 import { t } from "~/server/api/utils";
 import { logAuditEvent } from "~/server/audit";
+import { resolveTrustedClientIp } from "~/server/trusted-client-ip";
 import { env } from "~/env/server";
 import {
   AUTH_CONFIG,
@@ -328,39 +329,15 @@ async function cleanupExpiredRateLimits(): Promise<void> {
 }
 
 /**
- * Get client IP address from request headers.
+ * Get client IP address for a security decision (rate limiting, audit).
- * Only trusts X-Forwarded-For outside of local development (set by the Vercel
+ *
- * edge network in production; trusted in tests so the header-parsing path is
+ * Thin alias over `resolveTrustedClientIp` (./trusted-client-ip), which owns
- * exercised). In local development, uses the socket address to prevent header
+ * the trust order: the previous leftmost `x-forwarded-for` read was
- * spoofing.
+ * client-spoofable in our append-only proxy topology, and `x-real-ip` was
+ * read unconditionally — both fixed there (FRE-371).
  */
 export function getClientIP(event: H3Event): string {
-  // In production on Vercel, X-Forwarded-For is set by the edge network
+  return resolveTrustedClientIp(event);
-  // and cannot be spoofed by clients. In dev, ignore it.
-  if (env.NODE_ENV !== "development") {
-    const forwarded = getHeaderValue(event, "x-forwarded-for");
-    if (forwarded) {
-      return forwarded.split(",")[0].trim();
-    }
-    const realIP = getHeaderValue(event, "x-real-ip");
-    if (realIP) {
-      return realIP;
-    }
-  }
-
-  // Fallback: try socket remote address
-  try {
-    const nodeReq = event.node.req;
-    if (nodeReq?.socket?.remoteAddress) {
-      const addr = nodeReq.socket.remoteAddress;
-      // Clean up IPv6-mapped IPv4 addresses
-      return addr.replace(/^::ffff:/, "");
-    }
-  } catch {
-    // socket access failed
-  }
-
-  return "unknown";
 }
 
 /**

src/server/security/rate-limit.test.ts

@@ -150,29 +150,100 @@ describe("Rate Limiting", () => {
   });
 
   describe("getClientIP", () => {
-    it("should extract IP from x-forwarded-for header", () => {
+    // FRE-371: the read is spoof-resistant now. In the pinned topology
+    // (client → Cloudflare → origin proxy → app) both proxies APPEND, so
+    // x-forwarded-for arrives as `<spoof…>, <true client>, <CF edge>` and the
+    // leftmost hop is whatever the sender typed. Trust order:
+    // cf-connecting-ip, then x-forwarded-for rightmost-minus-one, then the
+    // socket peer — never the leftmost hop, never x-real-ip.
+
+    it("takes x-forwarded-for rightmost-minus-one, never the leftmost hop", () => {
       const event = createMockEvent({
-        headers: { "x-forwarded-for": "192.168.1.1, 10.0.0.1" }
+        headers: {
+          "x-forwarded-for": "6.6.6.6, 192.168.1.1, 10.0.0.1"
+        }
       });
 
       const ip = getClientIP(event);
       expect(ip).toBe("192.168.1.1");
     });
 
-    it("should extract IP from x-real-ip header", () => {
+    it("prefers cf-connecting-ip (Cloudflare overwrites it at the edge)", () => {
+      const event = createMockEvent({
+        headers: {
+          "cf-connecting-ip": "203.0.113.7",
+          "x-forwarded-for": "6.6.6.6, 192.168.1.1, 10.0.0.1"
+        }
+      });
+
+      const ip = getClientIP(event);
+      expect(ip).toBe("203.0.113.7");
+    });
+
+    it("a rotating leftmost x-forwarded-for does not change the resolved client", () => {
+      // The spoof the old read fell for: same Cloudflare-recorded client,
+      // different sender-chosen prefix per request. The key must be stable,
+      // or each rotation mints a fresh rate-limit bucket.
+      const first = getClientIP(
+        createMockEvent({
+          headers: {
+            "cf-connecting-ip": "203.0.113.7",
+            "x-forwarded-for": "1.1.1.1, 203.0.113.7, 10.0.0.1"
+          }
+        })
+      );
+      const second = getClientIP(
+        createMockEvent({
+          headers: {
+            "cf-connecting-ip": "203.0.113.7",
+            "x-forwarded-for": "2.2.2.2, 203.0.113.7, 10.0.0.1"
+          }
+        })
+      );
+
+      expect(first).toBe("203.0.113.7");
+      expect(second).toBe(first);
+    });
+
+    it("ignores x-real-ip entirely (client-settable in this topology)", () => {
       const event = createMockEvent({
         headers: { "x-real-ip": "192.168.1.2" }
       });
 
       const ip = getClientIP(event);
-      expect(ip).toBe("192.168.1.2");
+      expect(ip).toBe("unknown");
     });
 
-    it("should prefer x-forwarded-for over x-real-ip", () => {
+    it("ignores a client-supplied single-hop x-forwarded-for with no trusted proxy above it", () => {
+      // One hop only = the sender's own invention; discounting the trusted
+      // hop leaves nothing to believe.
       const event = createMockEvent({
+        headers: { "x-forwarded-for": "6.6.6.6" }
+      });
+
+      const ip = getClientIP(event);
+      expect(ip).toBe("unknown");
+    });
+
+    it("a non-loopback socket peer is the client and beats every header", () => {
+      const event = createMockEvent({
+        remoteAddress: "198.51.100.23",
         headers: {
-          "x-forwarded-for": "192.168.1.1",
+          "cf-connecting-ip": "6.6.6.6",
-          "x-real-ip": "192.168.1.2"
+          "x-forwarded-for": "6.6.6.6, 192.168.1.1, 10.0.0.1",
+          "x-real-ip": "6.6.6.6"
+        }
+      });
+
+      const ip = getClientIP(event);
+      expect(ip).toBe("198.51.100.23");
+    });
+
+    it("a loopback socket peer lets the forwarded headers speak", () => {
+      const event = createMockEvent({
+        remoteAddress: "127.0.0.1",
+        headers: {
+          "x-forwarded-for": "6.6.6.6, 192.168.1.1, 10.0.0.1"
         }
       });
 
@@ -198,13 +269,23 @@ describe("Rate Limiting", () => {
     it("should handle IPv6 addresses", () => {
       const event = createMockEvent({
         headers: {
-          "x-forwarded-for": "2001:0db8:85a3:0000:0000:8a2e:0370:7334"
+          "x-forwarded-for":
+            "2001:0db8:85a3:0000:0000:8a2e:0370:7334, 10.0.0.1"
         }
       });
 
       const ip = getClientIP(event);
       expect(ip).toBe("2001:0db8:85a3:0000:0000:8a2e:0370:7334");
     });
+
+    it("rejects a candidate hop that is not an address", () => {
+      const event = createMockEvent({
+        headers: { "x-forwarded-for": "not-an-ip, 10.0.0.1" }
+      });
+
+      const ip = getClientIP(event);
+      expect(ip).toBe("unknown");
+    });
   });
 
   describe("rateLimitLogin", () => {

src/server/security/test-utils.ts

@@ -14,12 +14,15 @@ export function createMockEvent(options: {
   cookies?: Record<string, string>;
   method?: string;
   url?: string;
+  /** Socket peer the server observed; omit for a peer-less synthetic event. */
+  remoteAddress?: string;
 }): H3Event {
   const {
     headers = {},
     cookies = {},
     method = "POST",
-    url = "http://localhost:3000/"
+    url = "http://localhost:3000/",
+    remoteAddress
   } = options;
 
   // Build the cookie header string from the cookies object only
@@ -49,7 +52,10 @@ export function createMockEvent(options: {
     headers: headersObj,
     node: {
       req: {
-        headers: allHeaders
+        headers: allHeaders,
+        ...(remoteAddress
+          ? { socket: { remoteAddress } }
+          : {})
       },
       res: {
         cookies: {}

src/server/trusted-client-ip.test.ts

@@ -0,0 +1,171 @@
+import { describe, expect, it } from "bun:test";
+
+import {
+  resolveTrustedClientIp,
+  isIpAddress,
+  isLoopbackAddress,
+  UNKNOWN_CLIENT_IP,
+  type ClientIpEventLike
+} from "./trusted-client-ip";
+
+/**
+ * Unit coverage for the security-path client-IP read (FRE-371). The caller
+ * suites (rate-limit.test.ts, report.test.ts) pin the behaviour through
+ * getClientIP and the route; this file pins the helper's own edges: the peer
+ * forms a real socket can present, the APIEvent wrapper, and failing closed.
+ */
+function event(opts: {
+  headers?: Record<string, string>;
+  remoteAddress?: string;
+  wrapped?: boolean;
+}): ClientIpEventLike {
+  const inner: ClientIpEventLike = {
+    ...(opts.remoteAddress
+      ? { node: { req: { socket: { remoteAddress: opts.remoteAddress } } } }
+      : {}),
+    request: { headers: new Headers(opts.headers ?? {}) }
+  };
+  // An APIEvent wraps its H3Event as `nativeEvent` (routes/api/* shape).
+  return opts.wrapped ? { nativeEvent: inner } : inner;
+}
+
+describe("resolveTrustedClientIp", () => {
+  it("trust order: non-loopback peer, then cf-connecting-ip, then rightmost-minus-one x-forwarded-for", () => {
+    // Peer wins.
+    expect(
+      resolveTrustedClientIp(
+        event({
+          remoteAddress: "198.51.100.23",
+          headers: {
+            "cf-connecting-ip": "203.0.113.7",
+            "x-forwarded-for": "6.6.6.6, 203.0.113.7, 10.0.0.1"
+          }
+        })
+      )
+    ).toBe("198.51.100.23");
+
+    // Loopback peer → Cloudflare's record.
+    expect(
+      resolveTrustedClientIp(
+        event({
+          remoteAddress: "127.0.0.1",
+          headers: {
+            "cf-connecting-ip": "203.0.113.7",
+            "x-forwarded-for": "6.6.6.6, 203.0.113.7, 10.0.0.1"
+          }
+        })
+      )
+    ).toBe("203.0.113.7");
+
+    // No CF header → the hop below the trusted proxy.
+    expect(
+      resolveTrustedClientIp(
+        event({
+          remoteAddress: "127.0.0.1",
+          headers: { "x-forwarded-for": "6.6.6.6, 203.0.113.7, 10.0.0.1" }
+        })
+      )
+    ).toBe("203.0.113.7");
+  });
+
+  it("reads the wrapped H3Event of an APIEvent-shaped input", () => {
+    expect(
+      resolveTrustedClientIp(
+        event({
+          wrapped: true,
+          remoteAddress: "127.0.0.1",
+          headers: { "cf-connecting-ip": "203.0.113.7" }
+        })
+      )
+    ).toBe("203.0.113.7");
+  });
+
+  it("never returns a truncated address", () => {
+    // The full /128 is the bucket key; a truncated one would pool attackers
+    // with their neighbours.
+    const ip = resolveTrustedClientIp(
+      event({
+        remoteAddress: "127.0.0.1",
+        headers: { "cf-connecting-ip": "2001:0db8:85a3:0000:0000:8a2e:0370:7334" }
+      })
+    );
+    expect(ip).toBe("2001:0db8:85a3:0000:0000:8a2e:0370:7334");
+  });
+
+  it("fails closed to the stricter unknown key", () => {
+    // One hop = the sender's own invention; a non-address hop; nothing at all.
+    expect(
+      resolveTrustedClientIp(
+        event({ headers: { "x-forwarded-for": "6.6.6.6" } })
+      )
+    ).toBe(UNKNOWN_CLIENT_IP);
+    expect(
+      resolveTrustedClientIp(
+        event({ headers: { "cf-connecting-ip": "not-an-ip" } })
+      )
+    ).toBe(UNKNOWN_CLIENT_IP);
+    expect(resolveTrustedClientIp(event({}))).toBe(UNKNOWN_CLIENT_IP);
+  });
+
+  it("recognises the loopback forms a real peer presents", () => {
+    expect(
+      resolveTrustedClientIp(
+        event({
+          // IPv6-mapped IPv4 loopback from a node socket.
+          remoteAddress: "::ffff:127.0.0.1",
+          headers: { "cf-connecting-ip": "203.0.113.7" }
+        })
+      )
+    ).toBe("203.0.113.7");
+    expect(
+      resolveTrustedClientIp(
+        event({
+          remoteAddress: "::1",
+          headers: { "cf-connecting-ip": "203.0.113.7" }
+        })
+      )
+    ).toBe("203.0.113.7");
+    // A non-loopback peer that merely looks odd is still the client.
+    expect(
+      resolveTrustedClientIp(
+        event({
+          remoteAddress: "::ffff:203.0.113.7",
+          headers: { "cf-connecting-ip": "6.6.6.6" }
+        })
+      )
+    ).toBe("203.0.113.7");
+  });
+
+  it("never believes x-real-ip", () => {
+    expect(
+      resolveTrustedClientIp(
+        event({ headers: { "x-real-ip": "203.0.113.7" } })
+      )
+    ).toBe(UNKNOWN_CLIENT_IP);
+  });
+});
+
+describe("address helpers", () => {
+  it("isIpAddress", () => {
+    expect(isIpAddress("203.0.113.7")).toBe(true);
+    expect(isIpAddress("::1")).toBe(true);
+    expect(isIpAddress("::ffff:203.0.113.7")).toBe(true);
+    expect(isIpAddress("2001:db8::1")).toBe(true);
+    expect(isIpAddress("not-an-ip")).toBe(false);
+    expect(isIpAddress("256.1.1.1")).toBe(false);
+    expect(isIpAddress("")).toBe(false);
+    expect(isIpAddress(null)).toBe(false);
+    expect(isIpAddress(undefined)).toBe(false);
+  });
+
+  it("isLoopbackAddress", () => {
+    expect(isLoopbackAddress("127.0.0.1")).toBe(true);
+    expect(isLoopbackAddress("127.255.0.3")).toBe(true);
+    expect(isLoopbackAddress("::1")).toBe(true);
+    expect(isLoopbackAddress("::ffff:127.0.0.1")).toBe(true);
+    expect(isLoopbackAddress("203.0.113.7")).toBe(false);
+    expect(isLoopbackAddress("::2")).toBe(false);
+    // Unparseable input is not loopback — fails closed.
+    expect(isLoopbackAddress("garbage")).toBe(false);
+  });
+});

src/server/trusted-client-ip.ts

@@ -0,0 +1,250 @@
+/**
+ * The client address, resolved for security decisions (FRE-371).
+ *
+ * This is the ONLY client-IP read allowed to feed a security decision — rate
+ * limiting, abuse quotas, account lockout, audit trails. It exists separately
+ * from `request-client.ts`'s `resolveClientIp` (the analytics read) on
+ * purpose:
+ *
+ *   - `resolveClientIp` carries a standing rule (FRE-369 review, 1d9287a):
+ *     it never feeds a security decision. Its blast radius is a poisoned
+ *     analytics row; ours is granting or denying access.
+ *   - Rate limiting needs the UN-truncated address; the analytics module only
+ *     ever hands out truncated prefixes.
+ *   - `request-client.ts` ships on FRE-366's branch, which is under review;
+ *     a security fix must not merge-depend on an analytics diff.
+ *
+ * The address-parsing primitives below are therefore a deliberate port of the
+ * reviewed ones, not an import. If the two ever drift, this file's version is
+ * the one security paths follow.
+ *
+ * WHY the old read was spoofable: `security.ts`'s `getClientIP` took the
+ * LEFTMOST `x-forwarded-for` hop, believing the header "cannot be spoofed".
+ * In the pinned topology — client → Cloudflare → same-host origin proxy →
+ * app — both proxies *append*, so the header arrives as
+ * `<client-supplied spoof…>, <true client>, <Cloudflare edge>` and the
+ * leftmost hop is exactly the one the sender chose. Rotating
+ * `X-Forwarded-For: <random>` per request minted a fresh rate-limit bucket
+ * and unlimited bug-report quota. `x-real-ip` was read unconditionally too;
+ * nothing in this topology overwrites it, so it is equally client text and is
+ * no longer read at all.
+ *
+ * Trust order (matches the convention FRE-366 landed after its security
+ * review, re-derived here for security stakes):
+ *
+ *   1. The direct socket peer, when it is a real routable address: it IS the
+ *      client (dev, direct hit), and any forwarded header from it is the
+ *      client describing itself — ignored.
+ *   2. `cf-connecting-ip` — reachable only when the peer is the loopback
+ *      origin proxy (or unreadable, e.g. a synthetic event in tests).
+ *      Cloudflare *overwrites* this header at the edge, so a client-supplied
+ *      value never survives. Must parse as an address.
+ *   3. `x-forwarded-for` counted from the RIGHT: drop the rightmost hop (the
+ *      Cloudflare edge address the origin proxy appended) and take the hop
+ *      before it. Never the leftmost. Must parse as an address.
+ *   4. "unknown" — callers give unknown-IP keys stricter shared limits, so
+ *      an unresolvable client fails toward a tighter bucket, never a looser
+ *      one.
+ *
+ * Deploy-side precondition this code cannot verify (same as the analytics
+ * read): the origin must be reachable only through Cloudflare and the
+ * same-host proxy. If the app is directly internet-reachable, a client can
+ * set every header read here and no in-app read can recover the truth.
+ */
+
+/** Cloudflare's "who actually connected" header: overwritten at the edge. */
+const CF_CONNECTING_IP = "cf-connecting-ip";
+const X_FORWARDED_FOR = "x-forwarded-for";
+
+/**
+ * Hops discounted from the right of `x-forwarded-for` before the value is
+ * taken: the Cloudflare edge address the origin proxy appended. Pinned to 1
+ * because there is exactly one trusted proxy between Cloudflare and the app;
+ * raise it only if the topology gains a trusted hop.
+ */
+const FORWARDED_HOPS_TO_DISCOUNT = 1;
+
+/** Returned when no trustworthy address exists. Callers rate-limit it harder. */
+export const UNKNOWN_CLIENT_IP = "unknown";
+
+/**
+ * The shapes this module reads: an H3Event (`security.ts` callers) or a
+ * SolidStart APIEvent (`routes/api/*`), which wraps its H3Event as
+ * `nativeEvent`. Every field is optional because test doubles are minimal;
+ * anything unreadable simply falls through to the next trust step.
+ */
+export interface ClientIpEventLike {
+  request?: { headers?: unknown };
+  headers?: unknown;
+  node?: {
+    req?: {
+      headers?: Record<string, unknown>;
+      socket?: { remoteAddress?: string };
+    };
+  };
+  nativeEvent?: ClientIpEventLike;
+}
+
+/**
+ * The client address for a security decision, per the trust order above.
+ * Never truncated: rate-limit buckets are per-address, and truncating would
+ * let an attacker share a bucket with the innocents behind their /24.
+ */
+export function resolveTrustedClientIp(event: ClientIpEventLike): string {
+  // An APIEvent's socket and (authoritative) headers live on the wrapped
+  // H3Event; a bare APIEvent-shaped double without one is read as-is.
+  const source = event.nativeEvent ?? event;
+
+  const peer = directPeer(source);
+  if (peer && isIpAddress(peer) && !isLoopbackAddress(peer)) return peer;
+
+  // The peer is the loopback origin proxy (or unreadable): forwarded headers
+  // may be believed, in the order above.
+  const connecting = cleanHop(headerValue(source, CF_CONNECTING_IP));
+  if (isIpAddress(connecting)) return connecting;
+
+  const hops = (headerValue(source, X_FORWARDED_FOR) ?? "")
+    .split(",")
+    .map(cleanHop)
+    .filter(Boolean);
+  const index = hops.length - 1 - FORWARDED_HOPS_TO_DISCOUNT;
+  if (index >= 0 && isIpAddress(hops[index])) return hops[index]!;
+
+  return UNKNOWN_CLIENT_IP;
+}
+
+/** The socket peer, IPv6-mapped IPv4 flattened (`::ffff:1.2.3.4` → `1.2.3.4`). */
+function directPeer(event: ClientIpEventLike): string | null {
+  try {
+    const addr = event.node?.req?.socket?.remoteAddress;
+    return addr ? addr.replace(/^::ffff:/, "") : null;
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Header read tolerant of every event shape in play: Fetch-style
+ * `request.headers.get`, an h3 `event.headers` (Headers or plain object), and
+ * the raw node request headers. Header names are case-insensitive per HTTP;
+ * the plain-object fallbacks lowercase to match how node and the test doubles
+ * store them.
+ */
+function headerValue(event: ClientIpEventLike, name: string): string | null {
+  try {
+    const fromHeaders = (h: unknown): string | null => {
+      if (!h) return null;
+      if (typeof (h as Headers).get === "function") {
+        return (h as Headers).get(name) ?? null;
+      }
+      if (typeof h === "object") {
+        const record = h as Record<string, unknown>;
+        const value = record[name] ?? record[name.toLowerCase()];
+        return typeof value === "string" ? value : null;
+      }
+      return null;
+    };
+
+    return (
+      fromHeaders(event.request?.headers) ??
+      fromHeaders(event.headers) ??
+      fromHeaders(event.node?.req?.headers)
+    );
+  } catch {
+    return null;
+  }
+}
+
+function cleanHop(value: string | null | undefined): string {
+  return (value ?? "").trim();
+}
+
+// ── Addresses: parse and validate ───────────────────────────────────────────
+// Ported from the reviewed `request-client.ts` (FRE-366 @ 1d9287a); see the
+// header comment for why this is a copy and not an import.
+
+/** Any address this file understands: a dotted quad or an IPv6 literal. */
+export function isIpAddress(value: string | null | undefined): boolean {
+  return value !== null && value !== undefined && addressBytes(value) !== null;
+}
+
+/**
+ * Whether an address is the loopback the production proxy presents.
+ *
+ * Parses rather than string-matches, so the forms a real peer can present in —
+ * `::ffff:127.0.0.53`, `0:0:0:0:0:0:0:1`, an IPv4-mapped literal — are all
+ * recognised. An address this does not parse is *not* loopback, which fails
+ * closed: forwarded headers from an unrecognised peer are ignored rather than
+ * believed (a non-loopback peer short-circuits before headers are read).
+ */
+export function isLoopbackAddress(ip: string): boolean {
+  const bytes = addressBytes(ip);
+  if (!bytes) return false;
+  if (bytes.length === 4) return bytes[0] === 127;
+
+  // IPv6 loopback ::1 — and ::ffff:127/8, which is loopback too.
+  const mapped = ipv4FromBytes(bytes);
+  if (mapped) return isLoopbackAddress(mapped);
+  const tail = bytes[15]!;
+  return bytes.slice(0, 15).every((byte) => byte === 0) && tail === 1;
+}
+
+function isIpv4(value: string): boolean {
+  const parts = value.split(".");
+  if (parts.length !== 4) return false;
+  return parts.every(
+    (part) => /^\d{1,3}$/.test(part) && Number(part) <= 255 && !/^0\d/.test(part)
+  );
+}
+
+/** 4 bytes for IPv4, 16 for IPv6 (including `::ffff:a.b.c.d`), else null. */
+function addressBytes(value: string): number[] | null {
+  const raw = value.trim().replace(/^\[|\]$/g, "").split("%")[0]!;
+  if (isIpv4(raw)) return raw.split(".").map(Number);
+  if (!raw.includes(":")) return null;
+
+  const halves = raw.split("::");
+  if (halves.length > 2) return null;
+  const compressed = halves.length === 2;
+
+  const head = groupsToBytes(halves[0] ?? "");
+  const tail = groupsToBytes(halves[1] ?? "");
+  if (!head || !tail) return null;
+
+  const total = head.length + tail.length;
+  if (compressed) {
+    if (total > 8) return null;
+    return [...head, ...new Array(8 - total).fill(0), ...tail].flatMap(split16);
+  }
+  if (total !== 8) return null;
+  return [...head, ...tail].flatMap(split16);
+}
+
+/** One side of `::` as 16-bit groups; a trailing `1.2.3.4` counts as two. */
+function groupsToBytes(side: string): number[] | null {
+  if (side === "") return [];
+  const out: number[] = [];
+  for (const part of side.split(":")) {
+    if (/^[0-9a-fA-F]{1,4}$/.test(part)) {
+      out.push(parseInt(part, 16));
+    } else if (isIpv4(part)) {
+      const o = part.split(".").map(Number);
+      out.push((o[0]! << 8) | o[1]!, (o[2]! << 8) | o[3]!);
+    } else {
+      return null;
+    }
+  }
+  return out;
+}
+
+function split16(group: number): number[] {
+  return [(group >> 8) & 0xff, group & 0xff];
+}
+
+/** The embedded IPv4 of an IPv4-mapped IPv6 address (`::ffff:1.2.3.4`), else null. */
+function ipv4FromBytes(bytes: number[]): string | null {
+  const prefix = bytes.slice(0, 10).every((byte) => byte === 0);
+  const marker = bytes[10] === 0xff && bytes[11] === 0xff;
+  if (!prefix || !marker) return null;
+  return `${bytes[12]}.${bytes[13]}.${bytes[14]}.${bytes[15]}`;
+}