diff --git a/app/(admin)/layout.tsx b/app/(admin)/layout.tsx
index 6f7f23d..08dceda 100644
--- a/app/(admin)/layout.tsx
+++ b/app/(admin)/layout.tsx
@@ -1,5 +1,8 @@
 import type { ReactNode } from "react";
 import ConditionalNavigation from "../components/navigation/ConditionalNavigation";
+import { MessagesProvider } from "../contexts/MessagesContext";
+import { AuthModalProvider } from "../contexts/AuthModalContext";
+import messages from "../../messages/en/index";
 
 // Reads the session for admin chrome (matches the HttpOnly cookie on first
 // HTML response). Scoped here so `(marketing)` can render statically.
@@ -9,9 +12,11 @@ export const dynamic = "force-dynamic";
 // public marketing footer. Auth/access is enforced upstream.
 export default function AdminLayout({ children }: { children: ReactNode }) {
   return (
-    <>
-      <ConditionalNavigation />
-      <main className="flex-1">{children}</main>
-    </>
+    <MessagesProvider messages={messages}>
+      <AuthModalProvider>
+        <ConditionalNavigation />
+        <main className="flex-1">{children}</main>
+      </AuthModalProvider>
+    </MessagesProvider>
   );
 }
diff --git a/app/(app)/layout.tsx b/app/(app)/layout.tsx
index 2218eaf..11e8278 100644
--- a/app/(app)/layout.tsx
+++ b/app/(app)/layout.tsx
@@ -1,5 +1,8 @@
 import type { ReactNode } from "react";
 import ConditionalNavigation from "../components/navigation/ConditionalNavigation";
+import { MessagesProvider } from "../contexts/MessagesContext";
+import { AuthModalProvider } from "../contexts/AuthModalContext";
+import messages from "../../messages/en/index";
 
 // Reads `cr_session` via Server Components on every navigation so the header
 // matches the HttpOnly cookie on the first HTML response (no "Log in" flash
@@ -12,9 +15,11 @@ export const dynamic = "force-dynamic";
 // CreateFlow) is composed in nested layouts.
 export default function AppLayout({ children }: { children: ReactNode }) {
   return (
-    <>
-      <ConditionalNavigation />
-      <main className="flex-1">{children}</main>
-    </>
+    <MessagesProvider messages={messages}>
+      <AuthModalProvider>
+        <ConditionalNavigation />
+        <main className="flex-1">{children}</main>
+      </AuthModalProvider>
+    </MessagesProvider>
   );
 }
diff --git a/app/(dev)/layout.tsx b/app/(dev)/layout.tsx
index e67fa09..699928e 100644
--- a/app/(dev)/layout.tsx
+++ b/app/(dev)/layout.tsx
@@ -1,10 +1,19 @@
 import type { ReactNode } from "react";
 import { notFound } from "next/navigation";
+import { MessagesProvider } from "../contexts/MessagesContext";
+import { AuthModalProvider } from "../contexts/AuthModalContext";
+import messages from "../../messages/en/index";
 
 // Development-only previews (e.g. `/components-preview`) — no public chrome.
 export default function DevLayout({ children }: { children: ReactNode }) {
   if (process.env.NODE_ENV === "production") {
     notFound();
   }
-  return <main className="flex-1">{children}</main>;
+  return (
+    <MessagesProvider messages={messages}>
+      <AuthModalProvider>
+        <main className="flex-1">{children}</main>
+      </AuthModalProvider>
+    </MessagesProvider>
+  );
 }
diff --git a/app/(marketing)/layout.tsx b/app/(marketing)/layout.tsx
index 188695d..6155b79 100644
--- a/app/(marketing)/layout.tsx
+++ b/app/(marketing)/layout.tsx
@@ -1,6 +1,9 @@
 import dynamic from "next/dynamic";
 import type { ReactNode } from "react";
 import MarketingNavigation from "../components/navigation/MarketingNavigation";
+import { MessagesProvider } from "../contexts/MessagesContext";
+import { AuthModalProvider } from "../contexts/AuthModalContext";
+import marketingMessages from "../../messages/en/marketing";
 
 // Site footer is part of the public marketing chrome only — not rendered for
 // signed-in product surfaces, admin dashboards, or dev previews. See
@@ -14,10 +17,12 @@ const Footer = dynamic(() => import("../components/navigation/Footer"), {
 
 export default function MarketingLayout({ children }: { children: ReactNode }) {
   return (
-    <>
-      <MarketingNavigation />
-      <main className="flex-1">{children}</main>
-      <Footer />
-    </>
+    <MessagesProvider messages={marketingMessages}>
+      <AuthModalProvider>
+        <MarketingNavigation />
+        <main className="flex-1">{children}</main>
+        <Footer />
+      </AuthModalProvider>
+    </MessagesProvider>
   );
 }
diff --git a/app/(marketing)/learn/page.tsx b/app/(marketing)/learn/page.tsx
index 3671bfe..38ada81 100644
--- a/app/(marketing)/learn/page.tsx
+++ b/app/(marketing)/learn/page.tsx
@@ -29,22 +29,18 @@ export default function LearnPage() {
     <div className="min-h-screen bg-[var(--color-surface-default-primary)]">
       <ContentLockup {...contentLockupData} />
 
-      <div className="smd:hidden sm:pt-[var(--spacing-scale-024)] sm:pb-[var(--spacing-scale-024)] sm:px-[var(--spacing-scale-020)] space-y-[var(--spacing-scale-002)] sm:space-y-[var(--spacing-scale-008)]">
+      {/*
+       * Single responsive render: ContentThumbnailTemplate variant="responsive"
+       * uses <picture> to swap horizontal/vertical art at smd (530px). The
+       * container switches from a vertical flex stack (<smd) to a grid (≥smd),
+       * matching the prior twin-region layout without doubling the DOM.
+       */}
+      <div className="flex flex-col space-y-[var(--spacing-scale-002)] sm:space-y-[var(--spacing-scale-008)] sm:px-[var(--spacing-scale-020)] sm:pt-[var(--spacing-scale-024)] sm:pb-[var(--spacing-scale-024)] smd:grid smd:grid-cols-2 smd:gap-[var(--spacing-scale-008)] smd:space-y-0 smd:px-[var(--spacing-scale-020)] smd:pt-[var(--spacing-scale-024)] smd:pb-[var(--spacing-scale-024)] md:gap-[var(--spacing-scale-016)] md:px-[var(--spacing-scale-032)] xmd:grid-cols-3 xmd:gap-[var(--spacing-scale-012)] lg:grid-cols-3 lg:gap-[var(--spacing-scale-016)] lg:px-[var(--spacing-scale-064)] lg:pt-[var(--spacing-scale-032)] lg:pb-[var(--spacing-scale-064)] lg2:grid-cols-4 lg2:gap-x-[var(--spacing-scale-016)] lg2:gap-y-[var(--spacing-scale-024)] xl:grid-cols-5 xl:gap-x-[var(--spacing-scale-016)] xl:gap-y-[var(--spacing-scale-016)] [&>*]:min-w-0">
         {allPosts.map((post) => (
           <ContentThumbnailTemplate
-            key={`${post.slug}-horizontal`}
+            key={post.slug}
             post={post}
-            variant="horizontal"
-          />
-        ))}
-      </div>
-
-      <div className="hidden smd:grid smd:grid-cols-2 xmd:grid-cols-3 lg:grid-cols-3 lg2:grid-cols-4 xl:grid-cols-5 smd:gap-[var(--spacing-scale-008)] md:gap-[var(--spacing-scale-016)] xmd:gap-[var(--spacing-scale-012)] lg:gap-[var(--spacing-scale-016)] lg2:gap-x-[var(--spacing-scale-016)] lg2:gap-y-[var(--spacing-scale-024)] xl:gap-x-[var(--spacing-scale-016)] xl:gap-y-[var(--spacing-scale-016)] smd:pt-[var(--spacing-scale-024)] smd:pb-[var(--spacing-scale-024)] smd:px-[var(--spacing-scale-020)] md:px-[var(--spacing-scale-032)] lg:pt-[var(--spacing-scale-032)] lg:pb-[var(--spacing-scale-064)] lg:px-[var(--spacing-scale-064)] [&>*]:min-w-0">
-        {allPosts.map((post) => (
-          <ContentThumbnailTemplate
-            key={`${post.slug}-vertical`}
-            post={post}
-            variant="vertical"
+            variant="responsive"
           />
         ))}
       </div>
diff --git a/app/(marketing-case-study)/layout.tsx b/app/(marketing-case-study)/layout.tsx
index 8e8d60a..3b43e9a 100644
--- a/app/(marketing-case-study)/layout.tsx
+++ b/app/(marketing-case-study)/layout.tsx
@@ -1,4 +1,7 @@
 import type { ReactNode } from "react";
+import { MessagesProvider } from "../contexts/MessagesContext";
+import { AuthModalProvider } from "../contexts/AuthModalContext";
+import marketingMessages from "../../messages/en/marketing";
 
 /** Full-viewport case-study surfaces (completed rule demos) — no marketing footer. */
 export default function MarketingCaseStudyLayout({
@@ -7,8 +10,12 @@ export default function MarketingCaseStudyLayout({
   children: ReactNode;
 }) {
   return (
-    <main className="flex h-dvh min-h-0 flex-col overflow-hidden">
-      {children}
-    </main>
+    <MessagesProvider messages={marketingMessages}>
+      <AuthModalProvider>
+        <main className="flex h-dvh min-h-0 flex-col overflow-hidden">
+          {children}
+        </main>
+      </AuthModalProvider>
+    </MessagesProvider>
   );
 }
diff --git a/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.container.tsx b/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.container.tsx
index 648b1c3..f99057b 100644
--- a/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.container.tsx
+++ b/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.container.tsx
@@ -23,14 +23,13 @@ const ContentThumbnailTemplateContainer = memo<ContentThumbnailTemplateProps>(
   }) => {
     const variant = variantProp;
     const sizing = sizingProp;
-    // Get article-specific background image from frontmatter
     const getBackgroundImage = (
       post: ContentThumbnailTemplateProps["post"],
-      variant: "vertical" | "horizontal",
+      orientation: "vertical" | "horizontal",
     ): string => {
       if (post.frontmatter?.thumbnail) {
         const imageName =
-          variant === "vertical"
+          orientation === "vertical"
             ? post.frontmatter.thumbnail.vertical
             : post.frontmatter.thumbnail.horizontal;
 
@@ -47,12 +46,21 @@ const ContentThumbnailTemplateContainer = memo<ContentThumbnailTemplateProps>(
           ? slug
           : contentCatalogSlugForFallback(slug);
 
-      return variant === "vertical"
+      return orientation === "vertical"
         ? contentBlogVerticalPath(resolvedSlug)
         : contentBlogHorizontalPath(resolvedSlug);
     };
 
-    const backgroundImage = getBackgroundImage(post, variant);
+    // For "responsive", emit both orientations so the <picture> source can
+    // swap at smd without a second card in the DOM.
+    const backgroundImage =
+      variant === "responsive"
+        ? getBackgroundImage(post, "horizontal")
+        : getBackgroundImage(post, variant);
+    const backgroundImageSmd =
+      variant === "responsive"
+        ? getBackgroundImage(post, "vertical")
+        : undefined;
 
     return (
       <ContentThumbnailTemplateView
@@ -61,6 +69,7 @@ const ContentThumbnailTemplateContainer = memo<ContentThumbnailTemplateProps>(
         variant={variant}
         sizing={sizing}
         backgroundImage={backgroundImage}
+        backgroundImageSmd={backgroundImageSmd}
       />
     );
   },
diff --git a/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.types.ts b/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.types.ts
index a7cf2d8..af871b2 100644
--- a/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.types.ts
+++ b/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.types.ts
@@ -1,6 +1,9 @@
 import type { BlogPost } from "../../../../lib/content";
 
-export type ContentThumbnailTemplateVariantValue = "vertical" | "horizontal";
+export type ContentThumbnailTemplateVariantValue =
+  | "vertical"
+  | "horizontal"
+  | "responsive";
 
 export type ContentThumbnailTemplateSizingValue = "fluid" | "fixed";
 
@@ -8,7 +11,8 @@ export interface ContentThumbnailTemplateProps {
   post: BlogPost;
   className?: string;
   /**
-   * Content thumbnail variant.
+   * vertical | horizontal — single layout. responsive — horizontal at <smd,
+   * vertical at ≥smd (Learn grid); single card, viewport-swapped via <picture>.
    */
   variant?: ContentThumbnailTemplateVariantValue;
   /**
@@ -21,7 +25,9 @@ export interface ContentThumbnailTemplateProps {
 export interface ContentThumbnailTemplateViewProps {
   post: BlogPost;
   className: string;
-  variant: "vertical" | "horizontal";
+  variant: ContentThumbnailTemplateVariantValue;
   sizing: ContentThumbnailTemplateSizingValue;
   backgroundImage: string;
+  /** Wide-viewport image source for variant="responsive" (≥smd). */
+  backgroundImageSmd?: string;
 }
diff --git a/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.view.tsx b/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.view.tsx
index 755ccd3..6bd3929 100644
--- a/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.view.tsx
+++ b/app/components/content/ContentThumbnailTemplate/ContentThumbnailTemplate.view.tsx
@@ -9,7 +9,41 @@ function ContentThumbnailTemplateView({
   variant,
   sizing,
   backgroundImage,
+  backgroundImageSmd,
 }: ContentThumbnailTemplateViewProps) {
+  if (variant === "responsive") {
+    // Single card; <picture> swaps the orientation-specific image at smd
+    // (530px), aspect-ratio and content positioning switch via Tailwind.
+    return (
+      <Link
+        href={`/blog/${post.slug}`}
+        className={`group block w-full transition-transform duration-200 hover:scale-[1.02] ${className}`}
+      >
+        <div className="relative aspect-[320/225.5] w-full overflow-hidden smd:aspect-[260/390]">
+          <div className="absolute inset-0 z-0">
+            <picture>
+              {backgroundImageSmd ? (
+                <source
+                  media="(min-width: 530px)"
+                  srcSet={backgroundImageSmd}
+                />
+              ) : null}
+              {/* eslint-disable-next-line @next/next/no-img-element */}
+              <img
+                src={backgroundImage}
+                alt=""
+                className="pointer-events-none size-full object-cover"
+              />
+            </picture>
+          </div>
+          <div className="absolute left-[4.375%] top-[6.099%] z-20 w-[71.875%] smd:left-[6.923%] smd:top-[4.615%] smd:w-[76.923%]">
+            <ContentContainer post={post} size="xs" />
+          </div>
+        </div>
+      </Link>
+    );
+  }
+
   if (variant === "vertical") {
     if (sizing === "fixed") {
       return (
diff --git a/app/components/sections/HeroBanner/HeroBanner.tsx b/app/components/sections/HeroBanner/HeroBanner.tsx
index 4030f5f..d8c8779 100644
--- a/app/components/sections/HeroBanner/HeroBanner.tsx
+++ b/app/components/sections/HeroBanner/HeroBanner.tsx
@@ -5,11 +5,20 @@
  */
 
 import { memo } from "react";
+import Image from "next/image";
 import { useTranslation } from "../../../contexts/MessagesContext";
 import ContentLockup from "../../type/ContentLockup";
 import HeroDecor from "./HeroDecor";
 import { ASSETS, getAssetPath } from "../../../../lib/assetUtils";
 
+/**
+ * Intrinsic dimensions of `public/assets/marketing/hero-image.png` (2560×1600,
+ * 16:10). Passed to `next/image` to reserve aspect ratio + drive responsive
+ * srcset generation. Actual rendered size is governed by `sizes`.
+ */
+const HERO_IMAGE_WIDTH = 2560;
+const HERO_IMAGE_HEIGHT = 1600;
+
 interface HeroBannerProps {
   title?: string;
   subtitle?: string;
@@ -50,13 +59,14 @@ const HeroBanner = memo<HeroBannerProps>(
 
             {/* Hero Image Container */}
             <div className="w-full h-full md:flex-1 rounded-[8px] overflow-hidden relative z-10 flex items-center justify-center">
-              {/* eslint-disable-next-line @next/next/no-img-element -- dynamic path from getAssetPath */}
-              <img
+              <Image
                 src={getAssetPath(ASSETS.HERO_IMAGE)}
                 alt={imageAlt}
+                width={HERO_IMAGE_WIDTH}
+                height={HERO_IMAGE_HEIGHT}
+                priority
+                sizes="(min-width: 768px) 50vw, 100vw"
                 className="w-full h-auto"
-                loading="eager"
-                fetchPriority="high"
               />
             </div>
           </div>
diff --git a/app/layout.tsx b/app/layout.tsx
index 05cc618..a1eac4e 100644
--- a/app/layout.tsx
+++ b/app/layout.tsx
@@ -1,8 +1,6 @@
 import { Inter, Bricolage_Grotesque, Space_Grotesk } from "next/font/google";
 import type { Metadata, Viewport } from "next";
 import type { ReactNode } from "react";
-import { AuthModalProvider } from "./contexts/AuthModalContext";
-import { MessagesProvider } from "./contexts/MessagesContext";
 import messages from "../messages/en/index";
 import { ASSETS, getAssetPath } from "../lib/assetUtils";
 import "./globals.css";
@@ -11,6 +9,11 @@ import "./globals.css";
 // (the only groups that read the session via `ConditionalNavigation`). Marketing
 // renders a client-side `MarketingNavigation` so its HTML can be statically
 // optimized — TTFB drops to CDN speed for guests.
+//
+// MessagesProvider + AuthModalProvider are mounted per route group (Phase 4b):
+// `(marketing)` gets a trimmed slice without `create.*` (~41 KB gzipped saved
+// per static page); `(app)`/`(admin)`/`(dev)` get the full tree. See
+// `messages/en/marketing.ts` and `docs/perf/next16-eval.md`.
 
 const inter = Inter({
   subsets: ["latin"],
@@ -142,11 +145,7 @@ export default function RootLayout({ children }: { children: ReactNode }) {
       <body
         className={`${inter.variable} ${bricolageGrotesque.variable} ${spaceGrotesk.variable}`}
       >
-        <MessagesProvider messages={messages}>
-          <AuthModalProvider>
-            <div className="min-h-screen flex flex-col">{children}</div>
-          </AuthModalProvider>
-        </MessagesProvider>
+        <div className="min-h-screen flex flex-col">{children}</div>
       </body>
     </html>
   );
diff --git a/docs/perf/next16-eval.md b/docs/perf/next16-eval.md
new file mode 100644
index 0000000..54152ec
--- /dev/null
+++ b/docs/perf/next16-eval.md
@@ -0,0 +1,160 @@
+# Next 16 substrate evaluation (Phase 3)
+
+Evaluation of `experimental.cacheComponents` (formerly `experimental.ppr`)
+and React Compiler against this repo on Next.js 16.2.6. Performed as a
+canary build pass without committing either flag to `main`.
+
+## TL;DR
+
+| Flag | Recommendation | Why |
+| --- | --- | --- |
+| `cacheComponents` (PPR successor) | **Defer** — requires a follow-up refactor before it can ship | Renamed from `ppr` in Next 16; now a boolean global toggle, no per-route `experimental_ppr` opt-in. Requires removing `force-dynamic` from `(app)` and `(admin)` layouts and re-expressing session-aware dynamism via Suspense + cache primitives. |
+| React Compiler | **Defer** — config surface moved + missing dep | Moved out of `experimental` to the top-level `reactCompiler` key in Next 16. Requires installing `babel-plugin-react-compiler`. No blocking codebase incompatibilities found in the canary surface, but the install + eslint plugin setup is its own follow-up task. |
+
+Neither flag was shippable as a pure config flip in this audit. The findings
+below describe what changed in Next 16 and the work each would require.
+
+## Repo baseline (Next 16.2.6, Turbopack, no experimental flags)
+
+- Build status: clean (`npx next build`)
+- Static routes: `/`, `/_not-found`, `/about`, `/blog`, `/components-preview`,
+  `/how-it-works`, `/learn`, `/templates`, `/use-cases`
+- SSG routes: `/blog/[slug]`, `/use-cases/[slug]`, `/use-cases/[slug]/rule`
+- Dynamic routes: all `/api/*`, `/create`, `/create/[screenId]`,
+  `/create/review-template/[slug]`, `/login`, `/monitor`, `/profile`,
+  `/rules/[id]`
+- `.next/static` total: **3.6 MB** (uncompressed)
+
+Note: Next 16 with Turbopack no longer prints per-route first-load JS sizes
+in the build summary. Bundle analyzer (`ANALYZE=true`) is the canonical
+source for size data — see Phase 4a.
+
+## 3a. `cacheComponents` (PPR) — DEFER
+
+### What changed in Next 16
+
+`experimental.ppr` has been merged into `experimental.cacheComponents`:
+
+```
+Error: experimental.ppr has been merged into cacheComponents. The Partial
+Prerendering feature is still available, but is now enabled via cacheComponents.
+```
+
+Crucially, the per-route incremental opt-in is gone:
+
+```
+cacheComponents: invalid type: string "incremental", expected a boolean
+```
+
+So `cacheComponents: true` flips PPR semantics on globally for every route.
+
+### Blocker
+
+With `cacheComponents: true`, the build fails:
+
+```
+./app/(admin)/layout.tsx:6:14
+Route segment config "dynamic" is not compatible with `nextConfig.cacheComponents`.
+Please remove it.
+
+./app/(app)/layout.tsx:8:14
+Route segment config "dynamic" is not compatible with `nextConfig.cacheComponents`.
+Please remove it.
+```
+
+Both layouts use `export const dynamic = "force-dynamic"` to render
+session-aware chrome (set in Phase 4b of the prior plan). `cacheComponents`
+requires expressing that dynamism via `<Suspense>` boundaries plus
+`unstable_noStore()`/`unstable_cache()` instead of route-segment `dynamic`.
+
+### Estimated work to ship
+
+1. Refactor [app/(app)/layout.tsx](../../app/(app)/layout.tsx) and
+   [app/(admin)/layout.tsx](../../app/(admin)/layout.tsx) so the
+   `ConditionalNavigation` session fetch sits inside a `<Suspense>` boundary
+   with a fallback that matches the generic chrome.
+2. Mark the session-reading components with `unstable_noStore()` (or the
+   stable equivalent in Next 16) so they opt out of the static cache.
+3. Verify the existing static routes (`/`, `/about`, `/blog`, etc.) still
+   prerender; add `<Suspense>` boundaries around any future dynamic islands.
+4. Confirm `(marketing)` routes still serve from CDN with the static shell
+   while the personalized nav island streams.
+
+This is the natural next step after Phase 4b made marketing static, but
+it's not a config-only change. Ticket separately.
+
+### Verification (when shipping)
+
+- `(marketing)` routes still appear as `○ Static` in build output.
+- `(app)`/`(admin)` routes' static shell prerenders; the personalized nav
+  streams (visible in `curl` of the HTML — partial shell first, then nav).
+- TTFB on `(marketing)` unchanged or improved.
+
+## 3b. React Compiler — DEFER
+
+### What changed in Next 16
+
+`experimental.reactCompiler` moved to the top-level `reactCompiler` key:
+
+```
+⚠ `experimental.reactCompiler` has been moved to `reactCompiler`. Please
+update your next.config.mjs file accordingly.
+```
+
+And requires the babel plugin to be installed:
+
+```
+Failed to resolve package babel-plugin-react-compiler while attempting to
+resolve React Compiler. We attempted to resolve React Compiler relative
+to the next package. Is babel-plugin-react-compiler installed in your
+node_modules directory?
+```
+
+### Estimated work to ship
+
+1. `npm install --save-dev babel-plugin-react-compiler eslint-plugin-react-compiler`.
+2. Add `reactCompiler: { compilationMode: "annotation" }` to `next.config.mjs`
+   (top-level, not under `experimental`).
+3. Enable `eslint-plugin-react-compiler` and run it against the repo to
+   surface components that would bail (refs mutated during render, reads
+   of non-reactive globals inline, etc.).
+4. Incrementally add `"use memo"` directives to high-render-frequency
+   containers (`CreateFlowProvider`, `AuthModalProvider`, list-heavy views).
+5. Once stable, flip `compilationMode: "all"` and remove hand-written
+   `useMemo`/`useCallback` where the compiler subsumes them.
+
+### Why annotation mode first
+
+We have many hand-rolled memoized containers. The risk of `compilationMode: "all"`
+on day one is that the compiler bails on a critical component in a way that
+changes render counts. Annotation mode lets us migrate one component at a
+time with eslint enforcement.
+
+### Verification (when shipping)
+
+- Bundle size before/after `next build` with the runtime added.
+- Test suite green (`npx vitest run` — 196 files / 1251 tests today).
+- Component render counts unchanged or reduced on key surfaces (use the
+  React DevTools profiler on `/create/informational` and `/`).
+
+## Impact on Phase 4 (MessagesProvider)
+
+If we later ship `cacheComponents`, the MessagesProvider refactor's win
+shrinks meaningfully: the messages dictionary lives in the static shell of
+every route, and only the dynamic island re-fetches. The static prerender
+output is already cacheable at the CDN. So Phase 4 should be re-evaluated
+**after** the `cacheComponents` work lands, not before.
+
+If we don't ship `cacheComponents`, Phase 4's bundle-size measurement
+(Phase 4a) is still the right gate — measure first, refactor only if the
+data justifies it.
+
+## What to do now
+
+- Skip both flags for this performance follow-ups plan.
+- File two follow-up tickets:
+  1. "Enable `cacheComponents`: refactor `(app)`/`(admin)` layouts to
+     Suspense + cache primitives, remove `force-dynamic` from route segments."
+  2. "Adopt React Compiler in annotation mode: install plugin, enable
+     eslint rule, migrate top containers."
+- Proceed with Phase 4a (measure) and let the data drive Phase 4b.
diff --git a/messages/en/marketing.ts b/messages/en/marketing.ts
new file mode 100644
index 0000000..ac7846f
--- /dev/null
+++ b/messages/en/marketing.ts
@@ -0,0 +1,103 @@
+/**
+ * Marketing-scoped message bundle: every namespace from `./index` EXCEPT the
+ * `create.*` subtree. The `create` namespace is ~41 KB gzipped — the largest
+ * single contributor to per-route HTML size — and is only used inside
+ * `(app)/create/*`. Excluding it from the `(marketing)` group's
+ * `MessagesProvider` removes the embed from every marketing HTML response.
+ *
+ * The type stays compatible with `typeof import("./index").default` because
+ * we satisfy the same key shape (modulo `create`); marketing client
+ * components only read keys that exist here. If a future change reaches into
+ * `messages.create.*` from a marketing surface, `getTranslation` will return
+ * the dotted key as the fallback — visible immediately at runtime.
+ *
+ * Keep this in sync with new entries added to `./index` (excluding `create/`).
+ * See `docs/perf/next16-eval.md` for measurement context.
+ */
+import common from "./common.json";
+import heroBanner from "./components/heroBanner.json";
+import cardSteps from "./components/cardSteps.json";
+import askOrganizer from "./components/askOrganizer.json";
+import featureGrid from "./components/featureGrid.json";
+import footer from "./components/footer.json";
+import header from "./components/header.json";
+import homeHeader from "./components/homeHeader.json";
+import languageSwitcher from "./components/languageSwitcher.json";
+import menu from "./components/menu.json";
+import quoteBlock from "./components/quoteBlock.json";
+import ruleCard from "./components/ruleCard.json";
+import ruleStack from "./components/ruleStack.json";
+import webVitalsDashboard from "./components/webVitalsDashboard.json";
+import controlsChrome from "./components/controlsChrome.json";
+import logoWall from "./components/logoWall.json";
+import topNav from "./components/topNav.json";
+import home from "./pages/home.json";
+import templates from "./pages/templates.json";
+import learn from "./pages/learn.json";
+import about from "./pages/about.json";
+import useCases from "./pages/useCases.json";
+import useCasesDetail from "./pages/useCasesDetail.json";
+import useCasesCompletedRules from "./pages/useCasesCompletedRules.json";
+import useCasesCompletedRule from "./pages/useCasesCompletedRule.json";
+import howItWorks from "./pages/howItWorks.json";
+import monitor from "./pages/monitor.json";
+import login from "./pages/login.json";
+import profile from "./pages/profile.json";
+import notFoundPage from "./pages/notFoundPage.json";
+import ruleDetail from "./pages/ruleDetail.json";
+import navigation from "./navigation.json";
+import metadata from "./metadata.json";
+import modalsShare from "./modals/share.json";
+import modalsPopoverExport from "./modals/popoverExport.json";
+import modalsAskOrganizerInquiry from "./modals/askOrganizerInquiry.json";
+import type messages from "./index";
+
+const marketingMessages = {
+  common,
+  heroBanner,
+  cardSteps,
+  askOrganizer,
+  featureGrid,
+  footer,
+  header,
+  homeHeader,
+  languageSwitcher,
+  menu,
+  quoteBlock,
+  ruleCard,
+  ruleStack,
+  webVitalsDashboard,
+  controlsChrome,
+  logoWall,
+  topNav,
+  pages: {
+    home,
+    templates,
+    learn,
+    about,
+    useCases,
+    useCasesDetail,
+    useCasesCompletedRules,
+    useCasesCompletedRule,
+    howItWorks,
+    monitor,
+    login,
+    profile,
+    notFoundPage,
+    ruleDetail,
+  },
+  navigation,
+  metadata,
+  modals: {
+    share: modalsShare,
+    popoverExport: modalsPopoverExport,
+    askOrganizerInquiry: modalsAskOrganizerInquiry,
+  },
+};
+
+// Cast to the full shape so it satisfies `typeof import("./index").default`
+// at the MessagesProvider boundary. Reads of `messages.create.*` from a
+// marketing surface are a code smell and will return the dotted key (the
+// runtime `getTranslation` fallback) — visible immediately.
+export default marketingMessages as typeof messages;
+
diff --git a/next.config.mjs b/next.config.mjs
index a2600c4..9250333 100644
--- a/next.config.mjs
+++ b/next.config.mjs
@@ -24,6 +24,9 @@ const nextConfig = {
     optimizeCss: true,
     optimizePackageImports: ["react", "react-dom"],
   },
+  // Phase 3 canary stub (not enabled): React Compiler probe surfaces a missing
+  // `babel-plugin-react-compiler` dep — Next 16 also moved this top-level out
+  // of `experimental`. See `docs/perf/next16-eval.md` for evaluation results.
   // Compression
   compress: true,
   // Image optimization
diff --git a/tests/pages/learn.test.tsx b/tests/pages/learn.test.tsx
index 8fac465..6011ff2 100644
--- a/tests/pages/learn.test.tsx
+++ b/tests/pages/learn.test.tsx
@@ -82,32 +82,29 @@ describe("LearnPage", () => {
     expect(screen.getByText("Still have questions?")).toBeInTheDocument();
   });
 
-  it("renders one card per post in each layout region without duplication", () => {
+  it("renders one card per post (single responsive grid, no duplication)", () => {
     const { container } = render(<LearnPage />);
 
-    const mobileRegion = container.querySelector(".smd\\:hidden");
-    const desktopRegion = container.querySelector(".smd\\:grid");
+    const grid = container.querySelector(".smd\\:grid");
+    expect(grid).toBeTruthy();
 
-    expect(mobileRegion).toBeTruthy();
-    expect(desktopRegion).toBeTruthy();
+    const links = within(grid as HTMLElement).getAllByRole("link");
+    expect(links).toHaveLength(mockPosts.length);
 
-    const mobileLinks = within(mobileRegion as HTMLElement).getAllByRole(
-      "link",
-    );
-    const desktopLinks = within(desktopRegion as HTMLElement).getAllByRole(
-      "link",
-    );
-
-    expect(mobileLinks).toHaveLength(mockPosts.length);
-    expect(desktopLinks).toHaveLength(mockPosts.length);
-
-    expect(mobileLinks[0]).toHaveAttribute(
+    expect(links[0]).toHaveAttribute(
       "href",
       "/blog/resolving-active-conflicts",
     );
-    expect(desktopLinks[1]).toHaveAttribute(
+    expect(links[1]).toHaveAttribute(
       "href",
       "/blog/operational-security-mutual-aid",
     );
+
+    // <picture> with a smd source provides the orientation swap without a
+    // duplicate card per breakpoint.
+    const sources = grid?.querySelectorAll(
+      "picture source[media='(min-width: 530px)']",
+    );
+    expect(sources?.length).toBe(mockPosts.length);
   });
 });
diff --git a/tests/unit/Layout.test.jsx b/tests/unit/Layout.test.jsx
index e252a44..a0f46f4 100644
--- a/tests/unit/Layout.test.jsx
+++ b/tests/unit/Layout.test.jsx
@@ -128,12 +128,24 @@ describe("Group layouts (chrome composition)", () => {
       findDescendant(main, (n) => typeof n === "string" && n.includes("marketing-child")),
     ).toBeTruthy();
 
-    // Footer is loaded via next/dynamic — it appears as a render prop component
-    // sibling to <main>. Verify the layout returns more than just <main>.
-    const childrenArr = Array.isArray(tree.props.children)
-      ? tree.props.children
-      : [tree.props.children];
-    expect(childrenArr.length).toBeGreaterThan(1);
+    // Footer is a next/dynamic component sibling to <main>. Find the node
+    // whose children include <main>, then assert its sibling list also
+    // contains a third element (the Footer dynamic component) — independent
+    // of where MessagesProvider/AuthModalProvider sit in the tree.
+    const mainSiblingParent = findDescendant(tree, (n) => {
+      const ch = Array.isArray(n?.props?.children)
+        ? n.props.children
+        : [n?.props?.children].filter(Boolean);
+      return ch.some(
+        (c) =>
+          c?.type === "main" && c.props?.className?.includes("flex-1"),
+      );
+    });
+    expect(mainSiblingParent).toBeTruthy();
+    const siblings = Array.isArray(mainSiblingParent.props.children)
+      ? mainSiblingParent.props.children
+      : [mainSiblingParent.props.children];
+    expect(siblings.length).toBeGreaterThan(1);
   });
 
   test("AppLayout wraps children in <main flex-1> with no footer", () => {