feat(showcase): route shell-docs analytics + middleware through runtime config

Migrate the remaining shell-docs consumers of NEXT_PUBLIC_* env vars
off of process.env reads and onto the runtime-config readers:

  - lib/providers/posthog-provider.tsx (client): the PostHog key is
    pulled inside PostHogProvider so the value reflects the current
    deploy's NEXT_PUBLIC_POSTHOG_KEY; empty string disables analytics
    via the existing truthiness gates around init/capture
  - lib/providers/scarf-pixel.tsx (client): pixel id read at render
    time; empty string returns null (existing no-op behavior preserved)
  - lib/hooks/use-google-analytics.tsx (client): GA tracking id read
    at hook invocation; empty string short-circuits via the existing
    `if (!GA_ID) return` guard
  - middleware.ts (Edge): POSTHOG_HOST is now resolved per-request via
    getRuntimeConfigEdge() (the Edge wrapper skips unstable_noStore()
    since next/cache is unavailable there and middleware always runs
    per-request anyway). Server-side POSTHOG_KEY is unchanged — it's
    not a NEXT_PUBLIC_* var.

Author: jpr5

showcase/shell-docs/src/lib/hooks/use-google-analytics.tsx

@@ -4,9 +4,13 @@ import { usePathname } from "next/navigation";
 import { useEffect } from "react";
 import ReactGA from "react-ga4";
 import { normalizePathnameForAnalytics } from "@/lib/analytics-utils";
+import { getRuntimeConfig } from "@/lib/runtime-config.client";
 
 export function useGoogleAnalytics() {
-  const GA_ID = process.env.NEXT_PUBLIC_GOOGLE_ANALYTICS_TRACKING_ID;
+  // Tracking ID is read at render time from the runtime config injected
+  // by the root layout. Empty string disables GA — the early return
+  // below already gates on truthiness.
+  const GA_ID = getRuntimeConfig().googleAnalyticsTrackingId;
 
   if (!GA_ID) {
     return;

showcase/shell-docs/src/lib/providers/posthog-provider.tsx

@@ -4,8 +4,8 @@ import { PostHogProvider as PostHogProviderBase } from "posthog-js/react";
 import posthog from "posthog-js";
 import { useEffect, useState, useRef } from "react";
 import { usePathname } from "next/navigation";
+import { getRuntimeConfig } from "@/lib/runtime-config.client";
 
-const POSTHOG_KEY = process.env.NEXT_PUBLIC_POSTHOG_KEY;
 // Reverse-proxied via /ingest/* rewrites in next.config.ts so requests
 // flow through the docs host instead of *.i.posthog.com — bypasses
 // ad blockers / tracking-protection that target the PostHog hostname.
@@ -26,6 +26,11 @@ export function PostHogProvider({ children }: { children: React.ReactNode }) {
   const [sessionId, setSessionId] = useState<string | null>(null);
   const isInitializedRef = useRef(false);
 
+  // Pull the PostHog key from the runtime config injected by the root
+  // layout — empty string means "analytics disabled in this env" and
+  // the init/capture branches below already gate on truthiness.
+  const POSTHOG_KEY = getRuntimeConfig().posthogKey;
+
   // Read session_id from URL only on client side to avoid hydration mismatch
   useEffect(() => {
     if (typeof window !== "undefined") {

showcase/shell-docs/src/lib/providers/scarf-pixel.tsx

@@ -1,9 +1,12 @@
 "use client";
 
 import React from "react";
+import { getRuntimeConfig } from "@/lib/runtime-config.client";
 
 export function ScarfPixel() {
-  const SCARF_PIXEL_ID = process.env.NEXT_PUBLIC_SCARF_PIXEL_ID;
+  // Pixel ID from the runtime config injected by the root layout —
+  // empty string disables the pixel (consumer no-ops on falsy).
+  const SCARF_PIXEL_ID = getRuntimeConfig().scarfPixelId;
   if (!SCARF_PIXEL_ID) return null;
   return (
     <img

showcase/shell-docs/src/middleware.ts

@@ -2,6 +2,7 @@ import { NextResponse } from "next/server";
 import type { NextFetchEvent, NextRequest } from "next/server";
 import { seoRedirects } from "@/lib/seo-redirects";
 import { stripRouteGroupSegmentsFromPathname } from "@/lib/route-groups";
+import { getRuntimeConfigEdge } from "@/lib/runtime-config";
 import registry from "@/data/registry.json";
 
 // ---------------------------------------------------------------------------
@@ -59,8 +60,15 @@ for (const entry of seoRedirects) {
 // PostHog tracking via fetch (Edge Runtime compatible — no posthog-node SDK)
 // ---------------------------------------------------------------------------
 
-const POSTHOG_HOST =
-  process.env.NEXT_PUBLIC_POSTHOG_HOST ?? "https://eu.i.posthog.com";
+// PostHog host is read at REQUEST time from the Edge runtime-config
+// reader (which is the same body as the Node reader but skips the
+// `unstable_noStore()` call that the Edge bundle can't import). This
+// keeps a single built artifact retargetable across Railway envs by
+// changing NEXT_PUBLIC_POSTHOG_HOST. The reader applies the same
+// `https://eu.i.posthog.com` fallback used before.
+function getPosthogHost(): string {
+  return getRuntimeConfigEdge().posthogHost;
+}
 const DISTINCT_ID_COOKIE = "ph_distinct_id";
 // ~2 years — long enough to meaningfully track returning visitors.
 const DISTINCT_ID_COOKIE_MAX_AGE = 60 * 60 * 24 * 365 * 2;
@@ -79,7 +87,7 @@ function trackRedirect(id: string, fromPath: string, toPath: string): void {
   }
 
   // Fire-and-forget — don't await
-  fetch(`${POSTHOG_HOST}/capture/`, {
+  fetch(`${getPosthogHost()}/capture/`, {
     method: "POST",
     headers: { "Content-Type": "application/json" },
     body: JSON.stringify({
@@ -106,7 +114,7 @@ async function capturePageView(
   }
 
   try {
-    const response = await fetch(`${POSTHOG_HOST}/capture/`, {
+    const response = await fetch(`${getPosthogHost()}/capture/`, {
       method: "POST",
       headers: { "Content-Type": "application/json" },
       body: JSON.stringify({