rpc audit: same-cohort compare links from product pages; /rpc title, description, H2

src/app/rpc/page.tsx

@@ -22,11 +22,11 @@ import { SITE } from "@/data/site";
  */
 
 const DESCRIPTION =
-  "RPC providers ranked per chain from 3 regions: free public endpoints with their URLs, and Alchemy, Chainstack, QuickNode on API-key endpoints, ranked separately. Live 24h p50 latency.";
+  "RPC providers ranked per chain from 3 regions: free public endpoints with URLs, plus Alchemy, Chainstack and QuickNode on API-key endpoints, ranked apart.";
 
 export const metadata: import("next").Metadata = pageMetadata({
   path: "/rpc",
-  title: "RPC providers by chain: public endpoints and API-key providers ranked by latency",
+  title: "RPC providers by chain: public and API-key endpoints, by latency",
   description: DESCRIPTION,
 });
 
@@ -117,7 +117,7 @@ export default async function RpcHubPage() {
       <header className="mb-8">
         <p className="label-mono text-sky-600 mb-2">RPC nodes</p>
         <h1 className="display text-4xl sm:text-5xl text-ink">
-          RPC providers by chain: public endpoints and API-key providers, ranked by latency
+          RPC providers by chain: public and API-key endpoints, ranked by latency
         </h1>
         <p className="mt-4 max-w-2xl text-base sm:text-lg text-ink-soft leading-snug">
           Every free, no-key public RPC endpoint, measured per chain with
@@ -249,7 +249,7 @@ export default async function RpcHubPage() {
       )}
 
       <footer className="mt-16 pt-6 border-t border-ink/10 text-[12px] text-ink-soft leading-relaxed">
-        <p className="label-mono text-ink-faint mb-2">Methodology</p>
+        <h2 className="label-mono text-ink-faint mb-2">Methodology</h2>
         <p>
           Each chain row aggregates that chain&apos;s dedicated bench: an
           identical JSON-RPC POST (<code>eth_getBlockByNumber(&quot;latest&quot;, false)</code> with

src/components/rpc-chains-leaderboard.tsx

@@ -152,7 +152,7 @@ export function RpcChainsLeaderboard({
                 dir={sortDir}
                 onClick={() => setSort("bestP90")}
               >
-                <span title="p90 latency of the same overall-best provider — the slow-tail number users actually feel. Empty when the provider's histogram doesn't have enough samples yet.">
+                <span title="p90 latency of the same overall-best provider, the slow-tail number users actually feel. Empty when the provider's histogram doesn't have enough samples yet.">
                   Best p90
                 </span>
               </ThSort>

src/lib/related-providers.ts

@@ -42,14 +42,37 @@ function isLiveAppearance(a: ProviderAppearance): boolean {
   return a.result.availability !== "unavailable" && a.result.ms.p50 > 0;
 }
 
+/** Two appearances on the same bench are comparable only in the same
+ *  access cohort: on a chain RPC page a public gateway and a keyed
+ *  provider are never ranked together, and the compare page
+ *  (sharedBenchSlugs) refuses the pair, so the link must too. */
+function sameCohort(a: ProviderAppearance, b: ProviderAppearance): boolean {
+  return (a.tier ?? null) === (b.tier ?? null);
+}
+
+/** Benches both providers appear on, same cohort only (live or not). */
+export function sharedBenchCount(
+  a: ProviderAppearance[],
+  b: ProviderAppearance[],
+): number {
+  const aByBench = new Map(a.map((x) => [x.benchmark.slug, x] as const));
+  let n = 0;
+  for (const x of b) {
+    const mine = aByBench.get(x.benchmark.slug);
+    if (mine && sameCohort(mine, x)) n += 1;
+  }
+  return n;
+}
+
 export function liveSharedBenchCount(
   a: ProviderAppearance[],
   b: ProviderAppearance[],
 ): number {
-  const aLive = new Set(a.filter(isLiveAppearance).map((x) => x.benchmark.slug));
+  const aLive = new Map(a.filter(isLiveAppearance).map((x) => [x.benchmark.slug, x] as const));
   let n = 0;
   for (const x of b) {
-    if (isLiveAppearance(x) && aLive.has(x.benchmark.slug)) n += 1;
+    const mine = aLive.get(x.benchmark.slug);
+    if (isLiveAppearance(x) && mine && sameCohort(mine, x)) n += 1;
   }
   return n;
 }
@@ -105,17 +128,13 @@ export const getCompareCandidates = cache(async function getCompareCandidates(
   const me = providerSlug.toLowerCase();
   const meProfile = profiles.find((p) => p.slug.toLowerCase() === me);
   if (!meProfile) return [];
-  const myBenches = new Set(meProfile.appearances.map((a) => a.benchmark.slug));
-  if (myBenches.size === 0) return [];
+  if (meProfile.appearances.length === 0) return [];
 
   const out: CompareCandidate[] = [];
   for (const other of profiles) {
     if (other.slug.toLowerCase() === me) continue;
     if (DEAD_COMPOSITE_SLUGS.has(other.slug.toLowerCase())) continue;
-    let shared = 0;
-    for (const a of other.appearances) {
-      if (myBenches.has(a.benchmark.slug)) shared += 1;
-    }
+    const shared = sharedBenchCount(meProfile.appearances, other.appearances);
     if (shared === 0) continue;
     const pairSlug = canonicalPairSlug(meProfile.slug, other.slug);
     // Only pairs whose compare page is indexable (see isPairLinkable).