⚡ Live Sandbox: AI Dev Tool: Pentium II at 600Mhz

📝 Editable Code Sandbox

```python
# AI Dev Tool: FastAPI Pydantic v2 Micro-SaaS Boilerplate with Next.js Expo Monorepo
# ==============================================================================
# This is a production-ready developer code asset for building high-performance
# Micro-SaaS applications using FastAPI, Pydantic v2, and Next.js Expo Monorepo.

from fastapi import FastAPI, Depends, HTTPException
from pydantic import BaseModel, validator
from typing import Optional
from nextjs import NextJSApp
from expo import ExpoApp

# Define the FastAPI application
app = FastAPI(
    title="FastAPI Pydantic v2 Micro-SaaS Boilerplate",
    description="A production-ready developer code asset for building high-performance Micro-SaaS applications.",
    version="1.0.0"
)

# Define the Pydantic model for user authentication
class User(BaseModel):
    """User authentication model."""
    username: str
    password: str

@validator("username")
    def validate_username(cls, v):
        """Validate the username."""
        if len(v) < 3:
            raise ValueError("Username must be at least 3 characters long.")
        return v

@validator("password")
    def validate_password(cls, v

🖥️ Interactive Execution Terminal Console

⚡ Ready! Click ▶️ Run Code to execute code in browser terminal...