v1.4.33 — polish and reliability

Quality-leap release between two HealthKit milestones. The headline is a P0 hotfix for the `/api/analytics` 500 that broke the Insights mother page for any account with more than a few thousand measurements: the six per-metric status helpers were spreading the entire numeric history into `Math.min` / `Math.max`, which trips a stack overflow once a single argument list exceeds the V8 spread cap. Both the surfaced symptom and the latent risk in five sibling helpers were folded onto a reduce-based min/max path.

Around that hotfix landed a deep polish pass: the Insights mother page now defers three below-the-fold blocks behind `next/dynamic` to trim the cold mount cost, the analytics endpoint gained a `?slice=summaries` slim slice that the per-metric sub-pages now ride, the Coach snapshot builder picked up a 60 s LRU keyed on `(userId, scope)`, the Settings shell consolidated three duplicate copies of the about / notifications / about-dropdown surfaces, the navigation strip dropped a redundant "Home" group label and a colliding "Notifications" sibling, every icon-only button on the medications and admin surfaces gained an accessible name, every Progress bar gained one too, three pages had their heading hierarchy repaired to a sequential h1 → h2 → h3, the mobile Coach FAB now hides while a chart tooltip is open so it cannot occlude the read-out, and the auth shell normalised every authenticated route to a single `max-w-screen-xl` container.

Also lands the Apple App Site Association handler at `/.well-known/apple-app-site-association` on every host that fronts the app, advertising the iOS bundle's App ID prefix (S8WDX4W5KX.dev.healthlog.app) under `webcredentials.apps` so the passkey ceremony shares cleanly between the web origin and the iOS app.

The release closes nineteen issues from a five-surface audit + a runtime bug-hunt pass, plus six follow-up tracks of polish across the affected surfaces.

src/components/monitoring/web-vitals-reporter.tsx

@@ -1,24 +1,62 @@
 "use client";
 
+import { useEffect, useRef } from "react";
 import { useReportWebVitals } from "next/web-vitals";
 
 /**
- * v1.4.28 R3d — client-side mount that pipes every Web Vitals
- * measurement to `/api/internal/web-vitals`.
+ * v1.4.28 R3d — client-side mount that pipes Web Vitals measurements
+ * to `/api/internal/web-vitals`.
  *
  * Next 16 ships `useReportWebVitals` as the supported hook for
  * capturing CLS / FCP / FID / LCP / TTFB / INP from the live
- * navigation. The hook fires once per metric per page load, so even a
- * heavy navigation produces at most six beacons.
+ * navigation. The hook fires once per metric per page load, so a
+ * heavy navigation can produce up to six beacons per route change.
+ *
+ * v1.4.33 F19 — the reporter previously posted EVERY measurement on
+ * EVERY page-load. In production the runtime audit captured
+ * `POST /api/internal/web-vitals 429` for almost every metric after
+ * the first navigation: six beacons × N navigations burned through
+ * the per-IP 60/min route-side rate-limit in seconds, so most samples
+ * were dropped before they reached the wide-event sink. Telemetry
+ * was self-throttled.
+ *
+ * Switch to client-side sampling at SAMPLE_RATE: each page-load
+ * decides ONCE (memoised via `useMemo`) whether to report and either
+ * sends every metric for that load or sends none. Per-load all-or-
+ * none keeps a sampled session's vitals coherent (the LCP from one
+ * page must be comparable to the CLS from the same page) while
+ * cutting traffic by an order of magnitude. The route-side rate-limit
+ * stays in place as a backstop against runaway sampling.
  *
  * Delivery transport: `navigator.sendBeacon` when available (queues
  * the POST without blocking the page lifecycle, survives the
  * `pagehide` event) with a `fetch({ keepalive: true })` fallback.
- * The route accepts the payload best-effort and returns 200 even on
+ * The route accepts the payload best-effort and returns 204 even on
  * malformed bodies — beacons must never delay or fail the navigation.
  */
+const SAMPLE_RATE = 0.1;
+
 export function WebVitalsReporter() {
+  // Decide once per mount whether this page-load reports its vitals.
+  // Math.random() is impure, so we deferred the draw to `useEffect`
+  // (React's purity contract forbids running impure work inside
+  // useMemo / the render body). The ref keeps the decision stable
+  // across every metric callback inside the same navigation —
+  // partial sampling would mix LCP-without-CLS noise into the wide-
+  // event aggregates. SSR initialises the ref to `null` (no sample
+  // decision yet); the first reportWebVitals callback fires post-
+  // hydration once the effect has filled the slot.
+  const sampledRef = useRef<boolean | null>(null);
+  useEffect(() => {
+    sampledRef.current = Math.random() < SAMPLE_RATE;
+  }, []);
+
   useReportWebVitals((metric) => {
+    // If the effect hasn't yet seeded the sample decision (very first
+    // pre-hydration measurement), drop the beacon — over-sampling at
+    // first paint would defeat the rate-limit relief.
+    if (sampledRef.current !== true) return;
+
     const body = JSON.stringify({
       id: metric.id,
       name: metric.name,