+-----------------------------------------------------------------------------------+
|                        INP INTERACTION LATENCY LIFECYCLE                          |
|                                                                                   |
|  [ 1. INPUT DELAY (0 ms - 50 ms) ] ────────────────────────────────────────────── |
|  * Time from user tap/click until the browser begins executing the event handler. |
|  * Cause of Lag: Main thread busy executing other background JavaScript tasks.    |
|                                │                                                  |
|                                ▼                                                  |
|  [ 2. PROCESSING DURATION (10 ms - 80 ms) ] ───────────────────────────────────── |
|  * Time spent executing the actual JavaScript event listener callbacks.           |
|  * Cause of Lag: Synchronous state loops, heavy JSON parsing, complex filtering.  |
|                                │                                                  |
|                                ▼                                                  |
|  [ 3. PRESENTATION DELAY (20 ms - 70 ms) ] ────────────────────────────────────── |
|  * Time spent recalculating styles, reflowing the layout, and painting pixels.    |
|  * Cause of Lag: Massive DOM size (>1,500 nodes), forced synchronous reflows.     |
|                                │                                                  |
|                                ▼                                                  |
|  [ TOTAL INP = Input Delay + Processing Duration + Presentation Delay (<200 ms) ] |
+-----------------------------------------------------------------------------------+

// scripts/profile-loaf.ts
if ('PerformanceObserver' in window && PerformanceObserver.supportedEntryTypes.includes('long-animation-frame')) {
  const observer = new PerformanceObserver((list) => {
    for (const entry of list.getEntries()) {
      const loaf = entry as any;
      console.warn(`[LoAF Detected] Duration: ${loaf.duration.toFixed(1)}ms | Blocking: ${loaf.blockingDuration.toFixed(1)}ms`);
      
      for (const script of loaf.scripts) {
        console.log(`  * Script: ${script.sourceURL}:${script.sourceCharPosition}`);
        console.log(`  * Function: ${script.sourceFunctionName} | Exec Time: ${script.executionDuration.toFixed(1)}ms`);
      }
    }
  });

  observer.observe({ type: 'long-animation-frame', buffered: true });
}

+-----------------------------------------------------------------------------------+
|                        4 PRODUCTION INP OPTIMIZATION TECHNIQUES                   |
|                                                                                   |
|  1. MAIN-THREAD YIELDING ────> Use scheduler.yield() to break up long loops.      |
|  2. WEB WORKER OFFLOADING ───> Offload CPU filtering & sorting to worker threads. |
|  3. DEBOUNCED EVENT HANDLERS ─> Limit execution frequency on resize & scroll.     |
|  4. OPTIMISTIC UI UPDATES ───> Render visual feedback before async API resolves.  |
+-----------------------------------------------------------------------------------+

// Modern Main-Thread Yielding Utility with Fallback
async function yieldToMainThread(): Promise<void> {
  if ('scheduler' in window && 'yield' in (window as any).scheduler) {
    await (window as any).scheduler.yield();
  } else {
    await new Promise((resolve) => setTimeout(resolve, 0));
  }
}

// Processing large dataset without blocking INP
async function processLargeProductFilter(items: any[]) {
  const filtered = [];
  for (let i = 0; i < items.length; i++) {
    // Process item
    if (items[i].inStock) filtered.push(items[i]);

    // Yield every 50 items to keep main-thread responsiveness under 50ms
    if (i % 50 === 0) {
      await yieldToMainThread();
    }
  }
  return filtered;
}

// workers/filter-worker.ts
self.onmessage = (e: MessageEvent) => {
  const { products, query } = e.data;
  const results = products.filter((p: any) =>
    p.title.toLowerCase().includes(query.toLowerCase())
  );
  self.postMessage(results);
};

// UI Component Event Listener (Main Thread Stays 100% Free!)
const worker = new Worker(new URL('./workers/filter-worker.ts', import.meta.url));

function handleSearchInput(e: React.ChangeEvent<HTMLInputElement>) {
  const query = e.target.value;
  // Visual input updates instantly (0ms INP lag)
  setSearchText(query);
  // Heavy search executes in background thread
  worker.postMessage({ products: allProducts, query });
}

// ❌ BAD: Forced Synchronous Layout (Triggers 120ms Reflow)
function updateCardsBad(elements: HTMLElement[]) {
  elements.forEach((el) => {
    const height = el.offsetHeight; // READ
    el.style.height = `${height + 10}px`; // WRITE (Triggers reflow next loop)
  });
}

// ✅ GOOD: Batched Reads and Writes (Executes in <4ms)
function updateCardsGood(elements: HTMLElement[]) {
  const heights = elements.map((el) => el.offsetHeight); // Batch READS
  elements.forEach((el, i) => {
    el.style.height = `${heights[i] + 10}px`; // Batch WRITES
  });
}

// Optimistic Button State Pattern
async function handleAddToCart(productId: string) {
  // 1. Instant Visual Feedback (<16ms paint)
  setButtonState('loading-spinner');
  
  try {
    // 2. Asynchronous API Execution
    await api.cart.add(productId);
    setButtonState('success');
  } catch (error) {
    setButtonState('error');
  }
}

// components/FastFilterList.tsx
import React, { useState, useTransition } from 'react';

export default function FastFilterList({ allItems }: { allItems: any[] }) {
  const [searchTerm, setSearchTerm] = useState('');
  const [filteredItems, setFilteredItems] = useState(allItems);
  const [isPending, startTransition] = useTransition();

  function handleFilterChange(e: React.ChangeEvent<HTMLInputElement>) {
    const value = e.target.value;
    
    // 1. High Priority: Input text updates synchronously (0ms INP delay)
    setSearchTerm(value);

    // 2. Low Priority: Heavy list re-render is marked as non-blocking transition
    startTransition(() => {
      const results = allItems.filter((item) =>
        item.name.toLowerCase().includes(value.toLowerCase())
      );
      setFilteredItems(results);
    });
  }

  return (
    <div>
      <input
        type="text"
        value={searchTerm}
        onChange={handleFilterChange}
        placeholder="Filter items..."
      />
      {isPending && <span className="loading-spinner">Updating...</span>}
      <ul>
        {filteredItems.map((item) => (
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
    </div>
  );
}

+-----------------------------------------------------------------------------------+
|                        BUGVISO INP MOBILE EMULATION PIPELINE                      |
|                                                                                   |
|  [ Web Application Submitted ] ──> [ FastAPI + ARQ Redis Worker Cluster ]         |
|                                         │                                         |
|                                         ▼                                         |
|  [ CDP THROTTLED PERFORMANCE DIAGNOSTIC ] ──────────────────────────────────────  |
|  ├── 1. 4x Mobile CPU Slowdown: Emulates budget mobile ARM processor execution    |
|  ├── 2. Slow 3G / Fast 3G Network: Emulates 400ms RTT latency and packet jitter   |
|  ├── 3. Synthetic Interaction Runner: Simulates clicks, scrolls, and typing       |
|  └── 4. LoAF Script Attribution: Isolates exact JS file & line causing INP lag    |
|                                         │                                         |
|                                         ▼                                         |
|  [ 0-100 HEALTH SCORE + ACTIONABLE DEVELOPER REMEDIATION PLAYBOOK ]               |
+-----------------------------------------------------------------------------------+