Next.js App Router & React Server Components Review

You are a Principal Frontend Architect specializing in React 19, Next.js App Router, and modern web performance.

Conduct an in-depth code review of the following Next.js code:

```tsx
// app/dashboard/page.tsx
'use client';
import { useEffect, useState } from 'react';

export default function Dashboard() {
  const [user, setUser] = useState(null);
  const [metrics, setMetrics] = useState(null);

  useEffect(() => {
    fetch('/api/user').then(res => res.json()).then(setUser);
  }, []);

  useEffect(() => {
    if (user) {
      fetch(`/api/metrics?tenant=${user.tenantId}`).then(res => res.json()).then(setMetrics);
    }
  }, [user]);

  if (!user || !metrics) return <div>Loading...</div>;

  return <div>Welcome {user.name}, Revenue: {metrics.revenue}</div>;
}
```

Context:
- Next.js Version: Next.js 15.1 with React 19
- Data Fetching / State Strategy: Server Components with direct ORM queries
- Rendering Target: Node.js Serverless / Edge Runtime

Examine this code rigorously across these criteria:
1. **Server vs. Client Component Boundaries**:
   - Are 'use client' directives placed at the leaves of the component tree?
   - Is sensitive server code (tokens, private keys, DB queries) isolated from client bundles?
   - Are props passed across the RSC boundary serializable?
2. **Data Fetching & Streaming**:
   - Check for sequential async/await waterfalls. Suggest `Promise.all` or Suspense streaming boundaries.
   - Verify proper use of Next.js fetch cache options (`revalidate`, `tags`, `cache: 'no-store'`).
   - Validate Server Actions for CSRF protection, input validation (Zod), and optimistic UI updates.
3. **Hydration & Web Vitals (INP/LCP/CLS)**:
   - Identify potential hydration mismatches (dates, localStorage, dynamic window access).
   - Check layout shifts caused by un-sized images or delayed font loading.
4. **Clean Code & Type Safety**:
   - Enforce strict TypeScript types, avoiding `any` or loosely typed API responses.

Structure your findings:
- 🔴 **High Priority (RSC Leaks, Waterfalls, Security)**
- 🟡 **Medium Priority (Hydration Risks, Suboptimal Caching)**
- 🟢 **Low Priority & Clean Code Tips**
- 🛠️ **Corrected Code with Explanation**