perf(startup): optimize Shiki and Monaco deferred loading

- Remove eager preloading of Shiki highlighter and Monaco editor from
  index.tsx startup path. Both now load purely on demand:
  - Shiki loads when a code block first appears in AI chat or file preview
  - Monaco loads when the user first opens/focuses an editor tab

- Remove preloadHighlighter() from shikiHighlighter.ts, add
  getPlainHighlightHtml() as a synchronous fallback for rendering code
  before Shiki loads (plain <pre> block with escaped HTML)

- Convert static MonacoManager import in FileEditHandlers to a lazy
  dynamic import, preventing monacoManager from being pulled into the
  CortexDesktopLayout bundle at parse time

- Add documentation clarifying the editor pool (EDITOR_POOL_SIZE = 4)
  is created on demand — no editors are pre-allocated in monacoManager.ts

Author: echobt

src/components/cortex/handlers/FileEditHandlers.tsx

@@ -7,14 +7,19 @@ import { useNavigate } from "@solidjs/router";
 import { useEditor } from "@/context/editor/EditorProvider";
 import { useSDK } from "@/context/SDKContext";
 import { fsWriteFile } from "@/utils/tauri-api";
-import { MonacoManager } from "@/utils/monacoManager";
 import { createLogger } from "@/utils/logger";
 import { getWindowLabel } from "@/utils/windowStorage";
 
 const logger = createLogger("FileEditHandlers");
 
+let _monacoMgr: typeof import("@/utils/monacoManager") | null = null;
+
 function getActiveMonacoEditor() {
-  const monaco = MonacoManager.getInstance().getMonacoOrNull();
+  if (!_monacoMgr) {
+    import("@/utils/monacoManager").then(m => { _monacoMgr = m; });
+    return null;
+  }
+  const monaco = _monacoMgr.MonacoManager.getInstance().getMonacoOrNull();
   if (!monaco) return null;
   const editors = monaco.editor.getEditors();
   for (const ed of editors) {

src/index.tsx

@@ -2,7 +2,7 @@ import { render } from "solid-js/web";
 import { Router, Route } from "@solidjs/router";
 import { lazy, Suspense } from "solid-js";
 import { initializeWindowStorage } from "@/utils/windowStorage";
-import { preloadHighlighter } from "@/utils/shikiHighlighter";
+
 // CRITICAL: Use AppShell instead of App for instant first paint
 // AppShell is minimal (~1KB) and lazy-loads AppCore (with 68 providers) after render
 import AppShell from "./AppShell";
@@ -43,39 +43,10 @@ logStartup("Window storage init done");
 // These resources are not needed for initial render but improve UX when accessed.
 // Loading during idle time prevents blocking the main thread during startup.
 
-function deferredPreload() {
-  // Preload Shiki highlighter for code blocks in chat/markdown
-  preloadHighlighter();
-  
-  // Preload Monaco editor for code editing
-  // This warms up the Monaco instance so it's ready when user opens a file
-  import("@/utils/monacoManager").then(({ MonacoManager }) => {
-    MonacoManager.getInstance().ensureLoaded().catch(() => {
-      // Silent fail - Monaco will load on demand if preload fails
-    });
-  });
-}
-
-/**
- * Second-pass preload: Removed - was causing Vite to add modulepreload
- * for heavy chunks, blocking startup.
- * 
- * These chunks will load naturally when AppCore imports them after first paint.
- * The lazy() wrapper in AppShell ensures they don't block initial render.
- */
-// function deferredPreloadPhase2() { /* removed */ }
-
-if ('requestIdleCallback' in window) {
-  // Phase 1: Critical preloads (Monaco, Shiki) - needed soon after startup
-  (window as any).requestIdleCallback(() => {
-    deferredPreload();
-  }, { timeout: 3000 });
-  
-  // Phase 2 removed - heavy context preloads were causing Vite modulepreload issues
-} else {
-  // Fallback: defer with setTimeout
-  setTimeout(() => deferredPreload(), 500);
-}
+// Monaco and Shiki are NOT preloaded here — they load on demand:
+// - Monaco loads when the user first opens/focuses an editor tab
+// - Shiki loads when a code block first appears in AI chat or file preview
+// This keeps the main bundle lean and avoids blocking startup.
 
 // ============================================================================
 // CODE SPLITTING: Lazy-loaded Pages

src/utils/monacoManager.ts

@@ -15,7 +15,11 @@ import type * as Monaco from "monaco-editor";
 // Constants
 // ============================================================================
 
-/** Number of editor instances to keep in the pool */
+/**
+ * Maximum number of editor instances in the pool.
+ * Pool is created on demand — no editors are pre-allocated.
+ * Editors are only instantiated in `acquireEditor()` when a tab is opened.
+ */
 const EDITOR_POOL_SIZE = 4;
 
 /** Delay before disposing unused models (ms) */

src/utils/shikiHighlighter.ts

@@ -211,17 +211,12 @@ export function detectLanguageFromPath(filePath: string): string {
 }
 
 /**
- * Preload highlighter in background (call after initial render)
+ * Lightweight synchronous fallback for rendering code before Shiki loads.
+ * Returns a plain `<pre>` block with escaped HTML — no syntax highlighting.
+ * Use this as the initial/placeholder render while `highlightCode()` resolves.
  */
-export function preloadHighlighter(): void {
-  const schedule = typeof requestIdleCallback !== "undefined"
-    ? requestIdleCallback
-    : (cb: () => void) => setTimeout(cb, 2000);
-  
-  schedule(() => {
-    // Just initialize the highlighter, don't preload languages
-    getHighlighter().catch(() => {});
-  });
+export function getPlainHighlightHtml(code: string, _language?: string): string {
+  return createPlainHtml(code);
 }
 
 /**