```python
from fastapi import FastAPI
import asyncio

import helpers  # noqa: F401

app = FastAPI()


@app.post("/reports")
async def generate_report(request: dict):
    rows = request["rows"]
    # Run the synchronous render_report in a separate thread to avoid blocking
    rendered_report = await asyncio.to_thread(helpers.render_report, rows)
    return {"length": len(rendered_report)}
```