diff --git a/eslint.config.js b/eslint.config.js
index ccf23ac..9bccbe3 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -44,10 +44,10 @@ export default tseslint.config(
     languageOptions: { globals: { ...globals.node } },
   },
 
-  // Plain JS config files (this file, etc.) are not part of the TS project —
-  // run them through the untyped ruleset only.
+  // Plain JS config files and Node scripts (this file, scripts/*.mjs, etc.) are
+  // not part of the TS project — run them through the untyped ruleset only.
   {
-    files: ['**/*.js'],
+    files: ['**/*.{js,mjs}'],
     extends: [tseslint.configs.disableTypeChecked],
     languageOptions: { globals: { ...globals.node } },
   },
diff --git a/package-lock.json b/package-lock.json
index dd1a39c..ea44ac3 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -40,6 +40,7 @@
         "@types/react": "^19.2.16",
         "@types/react-dom": "^19.2.3",
         "@vitejs/plugin-react": "^5.2.0",
+        "ajv": "^8.20.0",
         "eslint": "^10.4.1",
         "eslint-plugin-react-hooks": "^7.1.1",
         "eslint-plugin-react-refresh": "^0.5.2",
diff --git a/package.json b/package.json
index c5729f1..9578c15 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "description": "A browser-based snippet manager for Vega-Lite visualizations.",
   "scripts": {
     "dev": "vite",
-    "build": "tsc --noEmit && vite build",
+    "build": "tsc --noEmit && vite build && node scripts/check-light-entries.mjs",
     "preview": "vite preview",
     "typecheck": "tsc --noEmit",
     "test": "vitest run",
@@ -56,6 +56,7 @@
     "@types/react": "^19.2.16",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^5.2.0",
+    "ajv": "^8.20.0",
     "eslint": "^10.4.1",
     "eslint-plugin-react-hooks": "^7.1.1",
     "eslint-plugin-react-refresh": "^0.5.2",
diff --git a/public/_headers b/public/_headers
new file mode 100644
index 0000000..e31a272
--- /dev/null
+++ b/public/_headers
@@ -0,0 +1,10 @@
+# Cloudflare Pages header rules (copied into dist/ by Vite's public/ passthrough).
+#
+# Everything under /assets/ is content-hashed by the build (JS, CSS, and the
+# font files), so it is safe to cache forever — a changed file gets a new URL.
+# Without this rule CF Pages serves its default `max-age=14400, must-revalidate`,
+# making every returning visitor revalidate multi-MB vendor chunks every 4 hours.
+# HTML keeps the platform default (max-age=0, must-revalidate) so deploys
+# propagate instantly; icons live at the root un-hashed and keep the default too.
+/assets/*
+  Cache-Control: public, max-age=31536000, immutable
diff --git a/scripts/check-light-entries.mjs b/scripts/check-light-entries.mjs
new file mode 100644
index 0000000..61918b4
--- /dev/null
+++ b/scripts/check-light-entries.mjs
@@ -0,0 +1,47 @@
+// Post-build gate: the marketing entries stay light. The landing (/) and the
+// learning section (/learn/) must never gain a static edge into the heavy
+// vendor chunks — this shipped once (Vite's preload helper emitted inside the
+// monaco chunk chained every lazy import() to it; a vega-scale import in
+// theme-controls was reachable from Landing). Vite lists an entry's full
+// static graph as modulepreload links / module scripts in its HTML, so
+// grepping the emitted HTML catches any regression regardless of cause.
+//
+// Runs as part of `npm run build` (after `vite build`). Exit 1 on violation.
+import { existsSync, readFileSync, readdirSync } from 'node:fs';
+import { join } from 'node:path';
+
+const pages = ['dist/index.html', 'dist/learn/index.html'];
+if (existsSync('dist/learn')) {
+  for (const entry of readdirSync('dist/learn', { withFileTypes: true })) {
+    if (entry.isDirectory()) pages.push(join('dist/learn', entry.name, 'index.html'));
+  }
+}
+
+const HEAVY = /vendor-(?:monaco|vega)-[^"']*\.js/;
+const missing = pages.filter((p) => !existsSync(p));
+if (missing.length > 0) {
+  console.error(
+    `check-light-entries: expected pages missing from dist/:\n  ${missing.join('\n  ')}`,
+  );
+  process.exit(1);
+}
+// The gate bans chunks by name, so it must not fail open: if the names minted in
+// vite.config.ts (manualChunks) ever change, this makes the rename update the gate
+// instead of silently disarming it.
+const assets = readdirSync('dist/assets');
+for (const chunk of ['vendor-monaco', 'vendor-vega']) {
+  if (!assets.some((f) => f.startsWith(`${chunk}-`) && f.endsWith('.js'))) {
+    console.error(
+      `check-light-entries: no ${chunk}-*.js in dist/assets — chunk naming changed; update vite.config.ts manualChunks and this gate together.`,
+    );
+    process.exit(1);
+  }
+}
+const offenders = pages.filter((p) => HEAVY.test(readFileSync(p, 'utf8')));
+if (offenders.length > 0) {
+  console.error(
+    `check-light-entries: light entries reference heavy vendor chunks:\n  ${offenders.join('\n  ')}`,
+  );
+  process.exit(1);
+}
+console.log(`check-light-entries: OK (${pages.length} pages clean of vendor-monaco/vendor-vega)`);
diff --git a/src/app/components/ColorControls.tsx b/src/app/components/ColorControls.tsx
index 9ae887b..e9ab2a5 100644
--- a/src/app/components/ColorControls.tsx
+++ b/src/app/components/ColorControls.tsx
@@ -20,13 +20,8 @@
 
 import type { ReactNode } from 'react';
 import type { JsonObject } from '@core/spec-config';
-import {
-  type ConfigPath,
-  countSet,
-  getConfigValue,
-  schemeColors,
-  schemesByKind,
-} from '@core/theme-controls';
+import { type ConfigPath, countSet, getConfigValue, schemesByKind } from '@core/theme-controls';
+import { schemeColors } from '@core/scheme-colors';
 import { Button } from './Button';
 import { ColorField } from './ColorField';
 import { Icon } from './Icon';
diff --git a/src/core/scheme-colors.test.ts b/src/core/scheme-colors.test.ts
new file mode 100644
index 0000000..f2e02bc
--- /dev/null
+++ b/src/core/scheme-colors.test.ts
@@ -0,0 +1,24 @@
+import { describe, expect, it } from 'vitest';
+import { schemeColors } from './scheme-colors';
+
+describe('schemeColors', () => {
+  it('returns the full fixed palette for a categorical scheme (count ignored)', () => {
+    const colors = schemeColors('tableau10', 3);
+    expect(colors).toHaveLength(10);
+    expect(colors.every((c) => /^#[0-9a-f]{6}$/i.test(c))).toBe(true);
+  });
+
+  it('samples a continuous scheme at count stops, normalized to hex', () => {
+    const colors = schemeColors('viridis', 5);
+    expect(colors).toHaveLength(5);
+    expect(colors.every((c) => /^#[0-9a-f]{6}$/.test(c))).toBe(true);
+  });
+
+  it('samples the midpoint for a single continuous stop', () => {
+    expect(schemeColors('viridis', 1)).toHaveLength(1);
+  });
+
+  it('returns [] for an unknown scheme', () => {
+    expect(schemeColors('not-a-scheme')).toEqual([]);
+  });
+});
diff --git a/src/core/scheme-colors.ts b/src/core/scheme-colors.ts
new file mode 100644
index 0000000..2a62576
--- /dev/null
+++ b/src/core/scheme-colors.ts
@@ -0,0 +1,40 @@
+/**
+ * Named-scheme resolution to hex swatches (docs/exploration/chart-theming-scope.md §5).
+ *
+ * Split from theme-controls.ts because of the `vega-scale` import below:
+ * theme-controls is reachable from the landing/learn entry graphs (via
+ * `vega-themes`), and a static vega-scale edge there drags the vega vendor
+ * chunk into the marketing pages' eager JS (`scripts/check-light-entries.mjs`
+ * guards this after every build). Only the app's color controls resolve
+ * schemes to swatches, so the edge lives here, app-side of the split.
+ */
+
+import { scheme } from 'vega-scale';
+
+/**
+ * Resolve a named Vega scheme to hex swatches. A categorical scheme returns its
+ * fixed palette in full; a continuous scheme (sequential/diverging) is sampled
+ * at `count` evenly-spaced stops (`count` applies to continuous schemes only).
+ * Continuous interpolators yield `rgb(...)`, normalized to hex here. An unknown
+ * name returns `[]` — the picker shows that scheme without a preview rather than
+ * throwing. Used for the swatch/gradient preview and "materialize to swatches".
+ */
+export function schemeColors(name: string, count = 9): string[] {
+  const resolved: unknown = scheme(name);
+  if (Array.isArray(resolved)) return resolved.map((c) => toHex(String(c)));
+  if (typeof resolved === 'function' && count > 0) {
+    const interp = resolved as (t: number) => string;
+    if (count === 1) return [toHex(interp(0.5))];
+    return Array.from({ length: count }, (_, i) => toHex(interp(i / (count - 1))));
+  }
+  return [];
+}
+
+/** Normalize a CSS color to `#rrggbb`; passes through existing hex and unknowns. */
+function toHex(color: string): string {
+  if (color.startsWith('#')) return color;
+  const m = /rgba?\(\s*([\d.]+)\s*,\s*([\d.]+)\s*,\s*([\d.]+)/i.exec(color);
+  if (!m) return color;
+  const h = (n: string) => Math.round(Number(n)).toString(16).padStart(2, '0');
+  return `#${h(m[1])}${h(m[2])}${h(m[3])}`;
+}
diff --git a/src/core/theme-controls.test.ts b/src/core/theme-controls.test.ts
index 7d0c4ae..104c2cf 100644
--- a/src/core/theme-controls.test.ts
+++ b/src/core/theme-controls.test.ts
@@ -8,10 +8,10 @@ import {
   enumValue,
   getConfigValue,
   normalizeRangeSchemes,
-  schemeColors,
   schemesByKind,
   setConfigValue,
 } from './theme-controls';
+import { schemeColors } from './scheme-colors';
 
 describe('getConfigValue', () => {
   const config = { range: { category: ['#111', '#222'] }, mark: { color: '#333' } };
@@ -163,28 +163,6 @@ describe('leaf coercion', () => {
   });
 });
 
-describe('schemeColors', () => {
-  it('returns the full fixed palette for a categorical scheme (count ignored)', () => {
-    const colors = schemeColors('tableau10', 3);
-    expect(colors).toHaveLength(10);
-    expect(colors.every((c) => /^#[0-9a-f]{6}$/i.test(c))).toBe(true);
-  });
-
-  it('samples a continuous scheme at count stops, normalized to hex', () => {
-    const colors = schemeColors('viridis', 5);
-    expect(colors).toHaveLength(5);
-    expect(colors.every((c) => /^#[0-9a-f]{6}$/.test(c))).toBe(true);
-  });
-
-  it('samples the midpoint for a single continuous stop', () => {
-    expect(schemeColors('viridis', 1)).toHaveLength(1);
-  });
-
-  it('returns [] for an unknown scheme', () => {
-    expect(schemeColors('not-a-scheme')).toEqual([]);
-  });
-});
-
 describe('enumValue', () => {
   const options = [{ value: '' }, { value: 'start' }, { value: 'end' }] as const;
 
diff --git a/src/core/theme-controls.ts b/src/core/theme-controls.ts
index 93ff420..6ff0543 100644
--- a/src/core/theme-controls.ts
+++ b/src/core/theme-controls.ts
@@ -1,9 +1,8 @@
 /**
- * Theme Builder structured-control primitives (docs/chart-theming-scope.md §5).
+ * Theme Builder structured-control primitives (docs/exploration/chart-theming-scope.md §5).
  *
  * Pure core: the read/write transforms the builder's structured controls run on
- * a draft config, plus the named-color-scheme catalog and its resolution. Three
- * concerns:
+ * a draft config, plus the named-color-scheme catalog. Two concerns:
  *
  *  - **Path get/set** — read a value at a nested config path, and set one back
  *    immutably while preserving every sibling key at each level. That guarantee
@@ -15,16 +14,15 @@
  *    writes a minimal diff, never a default dump.
  *  - **Scheme catalog** — the named Vega color schemes the color controls offer,
  *    grouped by kind (categorical / sequential / diverging).
- *  - **Scheme resolution** (`schemeColors`) — a scheme name to hex swatches, for
- *    the picker preview and the "materialize to an editable array" action.
  *
- * `vega-scale` (a focused vega sub-package, like core's `vega-expression`) owns
- * the scheme registry; importing it here keeps the umbrella `vega` out of core.
- * The one control transform that predates this module, `applyFontToConfig`,
- * stays in custom-theme.ts with the record entity.
+ * Scheme *resolution* (name → hex swatches) lives in `scheme-colors.ts`: it
+ * imports the `vega-scale` registry, and this module is reachable from the
+ * landing/learn entry graphs (via `vega-themes`), which must stay free of
+ * static edges into the vega vendor chunk. The one control transform that
+ * predates this module, `applyFontToConfig`, stays in custom-theme.ts with the
+ * record entity.
  */
 
-import { scheme } from 'vega-scale';
 import { isJsonObject, type JsonObject } from './spec-config';
 
 // ── Path get/set ──────────────────────────────────────────────────────────
@@ -213,33 +211,3 @@ export const THEME_SCHEMES: ReadonlyArray<ThemeScheme> = [
 export function schemesByKind(kind: SchemeKind): ThemeScheme[] {
   return THEME_SCHEMES.filter((s) => s.kind === kind);
 }
-
-// ── Scheme resolution ───────────────────────────────────────────────────────
-
-/**
- * Resolve a named Vega scheme to hex swatches. A categorical scheme returns its
- * fixed palette in full; a continuous scheme (sequential/diverging) is sampled
- * at `count` evenly-spaced stops (`count` applies to continuous schemes only).
- * Continuous interpolators yield `rgb(...)`, normalized to hex here. An unknown
- * name returns `[]` — the picker shows that scheme without a preview rather than
- * throwing. Used for the swatch/gradient preview and "materialize to swatches".
- */
-export function schemeColors(name: string, count = 9): string[] {
-  const resolved: unknown = scheme(name);
-  if (Array.isArray(resolved)) return resolved.map((c) => toHex(String(c)));
-  if (typeof resolved === 'function' && count > 0) {
-    const interp = resolved as (t: number) => string;
-    if (count === 1) return [toHex(interp(0.5))];
-    return Array.from({ length: count }, (_, i) => toHex(interp(i / (count - 1))));
-  }
-  return [];
-}
-
-/** Normalize a CSS color to `#rrggbb`; passes through existing hex and unknowns. */
-function toHex(color: string): string {
-  if (color.startsWith('#')) return color;
-  const m = /rgba?\(\s*([\d.]+)\s*,\s*([\d.]+)\s*,\s*([\d.]+)/i.exec(color);
-  if (!m) return color;
-  const h = (n: string) => Math.round(Number(n)).toString(16).padStart(2, '0');
-  return `#${h(m[1])}${h(m[2])}${h(m[3])}`;
-}
diff --git a/vite.config.ts b/vite.config.ts
index f422260..fe7b4db 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -44,9 +44,38 @@ export default defineConfig({
         // Split the heavy vendors so the chunk graph stays legible and the PWA
         // can precache/update them independently of app code. Monaco and the
         // Vega stack are each multi-MB; isolating them keeps app rebuilds small.
-        manualChunks: {
-          monaco: ['monaco-editor'],
-          vega: ['vega', 'vega-lite', 'vega-embed'],
+        //
+        // Function form with explicit homes for every module the light and
+        // heavy graphs *share* — Rollup merges small shared modules into their
+        // biggest importer, which is how the landing's eager JS twice gained a
+        // static edge into a multi-MB vendor chunk:
+        //  - Vite's dynamic-import preload helper (a virtual module used by
+        //    every chunk that calls `import()`, monaco included) was absorbed
+        //    into the monaco chunk, chaining the landing's lazy chart embed to
+        //    all of Monaco. It gets its own micro-chunk.
+        //  - vega-themes (preset config data), vega-expression (+ its dep
+        //    vega-util), and json-stringify-pretty-compact (used by core's
+        //    json-format) are imported both by core modules the landing/learn
+        //    entries reach and by vega/vega-embed internals; unassigned, they
+        //    were absorbed into the vega chunk. They get a small shared
+        //    'vendor-light' chunk — the heavy chunk importing the light one is
+        //    fine, the reverse is not. vega-scale stays unassigned: after the
+        //    scheme-colors.ts split, only app code and vega internals reach it.
+        // `scripts/check-light-entries.mjs` asserts the invariant (no
+        // vendor-monaco/vendor-vega reference in the landing/learn HTML) after
+        // every build.
+        manualChunks: (id: string) => {
+          if (id.includes('vite/preload-helper')) return 'preload-helper';
+          if (!id.includes('node_modules')) return undefined;
+          if (id.includes('node_modules/monaco-editor/')) return 'vendor-monaco';
+          if (
+            /node_modules\/(vega-themes|vega-expression|vega-util|json-stringify-pretty-compact)\//.test(
+              id,
+            )
+          )
+            return 'vendor-light';
+          if (/node_modules\/(vega|vega-lite|vega-embed)\//.test(id)) return 'vendor-vega';
+          return undefined;
         },
       },
     },