@@ -116,7 +116,9 @@ components/                 # client components: report-view, repo-list,
                             # hero-search, menu-search, menu-toggle, breadcrumbs
                             # (route trail under the menu), workflow-sample,
                             # platform-config, sentry-provider,
-                            # toast-notification (copy feedback live region)
+                            # toast-notification (copy feedback live region),
+                            # report-warmup (idle-time rendering-library
+                            # warming on directory pages)
 lib/                        # shared logic (client + RSC): routes, fetcher,
                             # renderer, search, utils, host, rate-limiter,
                             # cache-manager, error-handler, repo-submission,
@@ -281,7 +283,15 @@ coverage there when introducing new markup patterns.
   the report's arrival causes no layout shift. The vizdom bridge
   (`public/widgets/vizdom-bridge.js`) serves the wasm from Cache Storage
   (versioned cache name) so repeat visits never re-download it regardless
-  of the host's HTTP cache headers.
+  of the host's HTTP cache headers. Directory pages (landing + user
+  listing) mount `components/report-warmup.jsx`, which — after window
+  load, at main-thread idle — warms the shared report rendering libraries
+  only (the vizdom bridge module/wasm, Chart.js + svg-pan-zoom no-cors
+  into the HTTP cache, the bundled template), never report data (listings
+  can hold thousands of repositories), so the first report a visitor opens
+  renders from local caches. The landing bundle budget e2e measures
+  through the window load event for this reason: post-load prefetches and
+  warm-up fetches never delay the landing's own first paint.
 - Search `<input>`s are injected by table-enhancer — `<input>` is FORBID in
   the renderer's sanitization allow-list, so it must never appear in the
   mustache template.
 
@@ -47,7 +47,8 @@ app/                          # Next.js App Router (static export): layout
 components/                   # Client components (search combobox, hero/menu
                               # search, menu toggle, workflow sample, user
                               # listing, report view, submission form,
-                              # platform-config context, sentry provider)
+                              # platform-config context, sentry provider,
+                              # report warm-up for directory pages)
 lib/                          # Shared logic consumed by client components and
                               # RSC alike (routes, fetcher, renderer, search,
                               # repo-submission, error-handler, rate-limiter,
 
@@ -9,6 +9,7 @@ import { userStaticParams } from '../../lib/static-params';
 import { reposForUser } from '../../lib/utils';
 import { isValidGitHubName } from '../../lib/routes';
 import RepoList from '../../components/repo-list';
+import ReportWarmup from '../../components/report-warmup';
 
 export const dynamicParams = false;
 
@@ -30,6 +31,11 @@ export default async function UserPage({ params }) {
   return (
     <Suspense fallback={<p className="loading" role="status">Loading&hellip;</p>}>
       <RepoList username={username} initialRepositories={repositories} />
+      {/* Directory page: warm the shared report rendering libraries during
+          idle time (vizdom wasm, Chart.js, svg-pan-zoom, the template —
+          never report data) so the first report a visitor opens renders
+          from local caches. */}
+      <ReportWarmup />
     </Suspense>
   );
 }
@@ -1,5 +1,6 @@
 import Link from 'next/link';
 import HeroSearch from './hero-search';
+import ReportWarmup from './report-warmup';
 import { buildRepositoryListUrl } from '../lib/routes.js';
 
 export const FEATURED_COUNT = 6;
@@ -30,6 +31,11 @@ export default function Landing({ repositories }) {
           </ul>
         </div>
       </section>
+      {/* Directory page: warm the shared report rendering libraries during
+          idle time (vizdom wasm, Chart.js, svg-pan-zoom, the template —
+          never report data) so the first report a visitor opens renders
+          from local caches. Renders nothing; never delays this page. */}
+      <ReportWarmup />
     </>
   );
 }
@@ -0,0 +1,127 @@
+'use client';
+
+// Report rendering-library warm-up for directory pages (landing, user
+// listing). Renders nothing; once the page has fully loaded AND the main
+// thread is idle, it warms the shared rendering libraries the first report
+// a visitor opens needs, so the report renders with them already in local
+// caches:
+//
+// - vizdom wasm (~4.8MB): the shared bridge module is injected exactly the
+//   way the report page injects it, so the binary is fetched once and stored
+//   in the bridge's versioned Cache Storage entry — the report page's own
+//   bridge import then resolves it locally with zero network.
+// - Chart.js + svg-pan-zoom: fetched no-cors into the HTTP cache; the
+//   report page's classic <script src> requests then hit the cache (the CDN
+//   serves both immutable), matching the later request mode exactly.
+// - The bundled report template: a same-origin fetch into the HTTP cache.
+//
+// Report DATA is deliberately never warmed: listings can hold thousands of
+// repositories and the one a visitor opens is unknowable in advance — only
+// the shared rendering pipeline is warmed. Every step is fire-and-forget
+// and fails silently (a cold cache is just the status quo), and nothing
+// ever delays the hosting page's own rendering (load + idle scheduling).
+// Popup-only widgets (sigma, graphology, graphlib-dot, the 3D force graph)
+// also stay cold by design: they load lazily on the report page and are
+// needed only on demand.
+
+import { useEffect, useRef } from 'react';
+import { withBasePath } from '../lib/base-path';
+// The idle warm-up loads the vizdom bridge module on directory pages; this
+// module installs the widget-readiness bridge the bridge reports through, so
+// a mark fired while warming reaches the registry a later client-side-navigated
+// report reads from (the module map keeps the already-evaluated bridge module
+// from re-running on the report page).
+import '../lib/widget-loader';
+
+const WIDGET_SCRIPTS = [
+  'https://cdn.jsdelivr.net/npm/chart.js@4.4.7/dist/chart.umd.min.js',
+  'https://cdn.jsdelivr.net/npm/svg-pan-zoom@3.6.1/dist/svg-pan-zoom.min.js'
+];
+
+/** Fire-and-forget fetch: warming is best-effort, failures are fine. */
+function warmFetch(url, options) {
+  fetch(url, options).catch(() => {});
+}
+
+/**
+ * Warms the report rendering libraries until a directory page visitor
+ * opens a report.
+ *
+ * @param {object} props - Warm-up configuration.
+ * @param {number} [props.fallbackDelayMs=1500] - Test seam: delay before the
+ *   warm when requestIdleCallback is unavailable.
+ * @returns {null} Nothing is rendered.
+ */
+export default function ReportWarmup({ fallbackDelayMs = 1500 }) {
+  const warmedRef = useRef(false);
+
+  useEffect(() => {
+    // The warm runs once per mount (warmedRef); re-renders are no-ops.
+    if (warmedRef.current) return undefined;
+    let cancelled = false;
+    let cancelIdle = () => {};
+    let bridgeScript = null;
+
+    /** Runs each warm step exactly once, best-effort. */
+    const warm = () => {
+      if (cancelled || warmedRef.current) return;
+      warmedRef.current = true;
+
+      // 1. vizdom wasm through the shared bridge module: same file, same
+      //    versioned Cache Storage entry as the report page uses.
+      const bridgeSrc = withBasePath('/widgets/vizdom-bridge.js');
+      const alreadyInjected = [...document.querySelectorAll('script[type="module"]')]
+        .some(script => (script.getAttribute('src') || script.src || '')
+          .endsWith('/widgets/vizdom-bridge.js'));
+      if (!alreadyInjected) {
+        const script = document.createElement('script');
+        script.type = 'module';
+        script.src = bridgeSrc;
+        document.body.appendChild(script);
+        bridgeScript = script;
+      }
+
+      // 2. Classic widget scripts into the HTTP cache (no-cors matches the
+      //    report page's classic <script src> requests).
+      WIDGET_SCRIPTS.forEach(src => warmFetch(src, { mode: 'no-cors' }));
+
+      // 3. The bundled report template.
+      warmFetch(withBasePath('/assets/refactor-first-report.mustache'));
+    };
+
+    /**
+     * Schedules the warm at the first idle moment after the page loads. The
+     * idle callback is registered without a forced timeout, so the browser
+     * fires it strictly at an idle opportunity rather than on a timer while
+     * the page may still be busy; engines without requestIdleCallback wait
+     * out an idle window (the fallback delay) before the warm starts.
+     */
+    const scheduleAtIdle = () => {
+      if (cancelled) return;
+      if (typeof window.requestIdleCallback === 'function') {
+        const handle = window.requestIdleCallback(warm);
+        cancelIdle = () => window.cancelIdleCallback?.(handle);
+      } else {
+        const timer = setTimeout(warm, fallbackDelayMs);
+        cancelIdle = () => clearTimeout(timer);
+      }
+    };
+
+    if (document.readyState === 'complete') {
+      scheduleAtIdle();
+    } else {
+      window.addEventListener('load', scheduleAtIdle, { once: true });
+    }
+    return () => {
+      cancelled = true;
+      window.removeEventListener('load', scheduleAtIdle);
+      cancelIdle();
+      // The bridge script is appended straight to <body> (outside React's
+      // knowledge); drop it again on unmount so a navigating-away page leaves
+      // no script behind.
+      if (bridgeScript) bridgeScript.remove();
+    };
+  }, [fallbackDelayMs]);
+
+  return null;
+}
@@ -7,19 +7,56 @@
 const readyWidgets = new Set();
 const pendingCallbacks = new Map(); // name -> callback[]
 
+// Runtime globals a widget's bridge/library materializes once it is actually
+// usable, keyed by normalized widget name. The vizdom bridge assigns
+// window.Vizdom once the WASM finishes initializing and the CDN scripts assign
+// their globals on evaluation; the bridges then notify this registry through
+// window.__rfMarkWidgetReady. A mark can still be lost, though: an idle-time
+// warm-up on a directory page (components/report-warmup.jsx) loads the vizdom
+// bridge before any report page bundle exists, so the mark fires into a
+// registry this page never sees, and a client-side navigation to a report
+// reuses the already-materialized module (the browser module map does not
+// re-run it). Readiness is therefore also decidable from the materialized
+// global itself, so a widget whose runtime already exists is ready even
+// without a mark landing in this page.
+const WIDGET_RUNTIME_GLOBALS = {
+    chart: 'Chart',
+    vizdom: 'Vizdom',
+    'svg-pan-zoom': 'svgPanZoom',
+    sigma: 'Sigma',
+    graphology: 'graphology',
+    'graphlib-dot': 'graphlibDot',
+    '3d-force-graph': 'ForceGraph3D',
+    'three-spritetext': 'SpriteText'
+};
+
+/** Returns the runtime global name a widget materializes, or null if unknown. */
+function widgetGlobalName(name) {
+    const key = String(name || '').trim().toLowerCase();
+    return Object.prototype.hasOwnProperty.call(WIDGET_RUNTIME_GLOBALS, key)
+        ? WIDGET_RUNTIME_GLOBALS[key]
+        : null;
+}
+
 function installGlobalBridge() {
   if (typeof window === 'undefined') return;
   if (typeof window.__rfMarkWidgetReady !== 'function') {
     window.__rfMarkWidgetReady = name => markWidgetReady(name);
   }
 }
 
+// Install the browser-global bridge as soon as the registry module exists, so
+// marks fired before any report page has mounted (an idle-time warm-up on a
+// directory page) reach this registry — client-side navigations to report
+// pages share this module instance.
+installGlobalBridge();
+
 // Register a callback fired once the named widget is ready. If the widget
 // is already ready the callback runs synchronously. Returns an unsubscribe
 // function that removes a still-pending callback.
 export function onWidgetReady(name, callback) {
   installGlobalBridge();
-  if (readyWidgets.has(name)) {
+  if (isWidgetReady(name)) {
     callback();
     return () => {};
   }
@@ -47,14 +84,17 @@ export function markWidgetReady(name) {
 }
 
 export function isWidgetReady(name) {
-  return readyWidgets.has(name);
+  if (readyWidgets.has(name)) return true;
+  const globalName = widgetGlobalName(name);
+  if (globalName && typeof window !== 'undefined' && window[globalName]) return true;
+  return false;
 }
 
 // Wait until a widget is ready (or settles as failed). Returns a promise
 // that resolves with `true` when ready and `false` on timeout.
 export function waitForWidget(name, { timeoutMs = 5000 } = {}) {
   installGlobalBridge();
-  if (readyWidgets.has(name)) return Promise.resolve(true);
+  if (isWidgetReady(name)) return Promise.resolve(true);
   return new Promise(resolve => {
     const timer = setTimeout(() => resolve(false), timeoutMs);
     onWidgetReady(name, () => {