Page Transition Animation

---
name: page-transition-animation
description: "Use when implementing, optimizing, and timing 60fps/120fps page transition animation animations, transitions, gesture physics, and reduced-motion fallbacks."
version: 6.0.0
last-updated: 2026-09-29
skills:
  - framer-motion-expert
  - 60fps-animation
  - accessible-animation
tools: Read, Grep, Glob, Bash, Edit, Write
scripts-binding:
  - .agent/scripts/lint_runner.js
  - .agent/scripts/verify_all.js
---

# Page Transition Animation — Native & Framework Route Motion

## Mandatory Pre-Flight Context Inspection
Before reading, generating, or refactoring code in the `page-transition-animation` domain, inspect these 5 critical parameters:
1. **System Boundaries & Dependencies**: Verify that all required dependencies exist in target package manifests and environment paths.
2. **Runtime Context & Platform Invariants**: Confirm target platform constraints (Node.js, Browser, Mobile OS, Edge runtime) before applying APIs.
3. **Execution Guardrails**: Identify potential side-effects, state mutations, and unhandled asynchronous exceptions.
4. **Validation & Type Contracts**: Validate input data schemas and strict type constraints across all module interfaces.
5. **Observability & Proof of Execution**: Ensure execution produces tangible verification signals (terminal output, tests, metrics).


## Activation Boundaries
- **Activate when:** Use when implementing, optimizing, and timing 60fps/120fps page transition animation animations, transitions, gesture physics, and reduced-motion fallbacks.
- **DO NOT activate when:** The task falls outside the `page-transition-animation` domain or is managed by a different dedicated specialist agent.


## 🔁 Multi-Pass Execution Protocol

| Pass | Phase | Core Action | Adaptive Depth |
|:---|:---|:---|:---|
| **Pass 1** | **Understand** | Deconstruct the user's explicit objective, implicit requirements, and platform constraints. | Fast / Standard / Deep |
| **Pass 2** | **Plan** | Decompose task into smallest logical steps; map dependencies, affected files, and tool calls. | Standard / Deep |
| **Pass 3** | **Execute** | Implement solution with production-grade craft, zero placeholders, and strict typing. | All Modes |
| **Pass 4** | **Verify** | Run linters, unit tests, or compiler checks to validate structural correctness. | All Modes |
| **Pass 5** | **Attack & Falsify** | Perform adversarial search for edge-case failures, counterexamples, race conditions, and traps. | Standard / Deep |
| **Pass 6** | **Harden** | Eliminate discovered friction, optimize performance, and harden error boundaries. | Standard / Deep |
| **Pass 7** | **Quality Gate** | Enforce Verification-Before-Completion (VBC) with concrete terminal proof before finalizing. | All Modes |


---

## 🛠️ Technical Architecture & Reference Recipes

---

## 3 Page Transition Architectures

### 1. Native Web View Transitions API

The modern web standard for seamless page transitions (works across MPAs and SPAs):

```javascript
// Native JS navigation trigger
function navigateToPage(url) {
  if (!document.startViewTransition) {
    window.location.href = url;
    return;
  }

  document.startViewTransition(async () => {
    await updateDOMForUrl(url);
  });
}
```

```css
/* CSS View Transition Customization */
::view-transition-old(root) {
  animation: 200ms cubic-bezier(0.4, 0, 1, 1) both fade-out;
}
::view-transition-new(root) {
  animation: 300ms cubic-bezier(0, 0, 0.2, 1) both fade-in;
}

/* Shared Element Transition (e.g. Card Image to Detail Hero) */
.hero-image {
  view-transition-name: product-hero-image;
}
```

### 2. Next.js App Router + Framer Motion (`AnimatePresence`)

```tsx
'use client';

import { usePathname } from 'next/navigation';
import { AnimatePresence, motion } from 'framer-motion';

export function RouteLayoutWrapper({ children }: { children: React.ReactNode }) {
  const pathname = usePathname();

  return (
    <AnimatePresence mode="wait">
      <motion.div
        key={pathname}
        initial={{ opacity: 0, y: 8 }}
        animate={{ opacity: 1, y: 0 }}
        exit={{ opacity: 0, y: -8 }}
        transition={{ duration: 0.22, ease: [0.16, 1, 0.3, 1] }}
      >
        {children}
      </motion.div>
    </AnimatePresence>
  );
}
```

## 🚨 Edge-Case & Failure Mode Matrix

| Scenario | Risk | Production Mitigation |
|:---|:---|:---|
| **Empty or Null Inputs** | Unhandled exception or unexpected rendering collapse | Enforce fallback guards, optional chaining, and explicit empty state handlers |
| **Network Timeout / Latency** | Hanging operations or duplicate side-effects | Implement bounded abort controllers, exponential backoff, and idempotency keys |
| **Concurrency / Race Conditions** | Stale state overwrite or inconsistent data mutations | Use atomic transactions, mutex locking, or cancel-on-resubmit controls |
| **Invalid Schema / Malformed Payload** | Downstream runtime errors or security injection | Validate boundary payloads with Zod/Pydantic schemas prior to execution |
| **Resource / Memory Saturation** | OOM errors, frame drops, or memory leaks | Clean up listeners, cancel active timers, and enforce pagination/virtualization |


## 🤖 LLM-Specific Traps Table

| Anti-Pattern | What AI Commonly Does Wrong | What Is Actually Correct |
|:---|:---|:---|
| **The Instant Pop Trap** | Conditionally unmounting elements without animated interpolation | Use AnimatePresence or coordinate morphs with continuous geometry |
| **Layout Thrashing** | Animating width, height, top, or left inside animation loops | Animate composite-only transform (translate3d, scale) and opacity |
| **Sluggish Duration** | Setting micro-interaction transitions to 600ms+ causing interface lag | Cap interactive feedback at 160ms–240ms with snappy ease-out curves |


## 🏛️ Tribunal Verification & Guardrails

**Active Reviewers:** `frontend-reviewer` · `motion-reviewer` · `ui-ux-auditor`
**Slash Command:** `/review` or `/tribunal-full`

### 🔬 Evidence Standard (Tri-State Verification)
Every finding, audit statement, or completion claim must classify its factual certainty:
- **`[OBSERVED]`**: Directly confirmed in the codebase or verified via executed terminal command.
- **`[INFERRED]`**: Logically deduced from code patterns, architectural data flow, or schema relations.
- **`[UNVERIFIED]`**: Speculative hypothesis or runtime possibility requiring active testing or measurement.

### ✅ Pre-Flight Self-Audit Checklist
```
✅ Does animation maintain 60fps/120fps using transform (translate3d, scale) and opacity?
✅ Is optical mass conserved across state interpolations without volume collapse?
✅ Is duration capped within micro-interaction budgets (150ms–280ms)?
✅ Is prefers-reduced-motion respected with graceful instant fallbacks?
✅ Did I prevent layout thrashing and continuous geometry mutations?
```

### 🛑 Verification-Before-Completion (VBC) Protocol
**CRITICAL:** You must follow a strict "evidence-based closeout" state machine.
- ❌ **Forbidden:** Declaring a task complete because the output "looks correct."
- ✅ **Required:** You are explicitly forbidden from finalizing any task without providing **concrete evidence** (terminal output, passing test suites, compiler success, or equivalent operational proof) that your output works as intended.