```python
from fastapi import FastAPI
import asyncio
import helpers  # noqa: F401

app = FastAPI()

@app.get("/portfolio")
async def portfolio(symbols: str):
    # Parse comma-separated symbols, stripping whitespace
    symbols_list = [sym.strip() for sym in symbols.split(",")]
    # Create an async fetch task for each symbol
    tasks = [helpers.afetch_price(sym) for sym in symbols_list]
    # Run all fetches concurrently (non‑blocking)
    prices = await asyncio.gather(*tasks)
    # Build the required response format
    prices_dict = {sym: price for sym, price in zip(symbols_list, prices)}
    return {"prices": prices_dict}
```