=== Edge Case Verification ===

1. OpenWeatherMap requires key: True
   -> Source correctly gated
2. FRED requires key: True
   -> Source correctly gated
3. All requires-key sources: ['openweathermap', 'fred']
   -> Correct: only OPENWEATHERMAP and FRED
4. Sources for CRYPTO category: ['newsapi', 'reddit', 'coingecko', 'coincap']
   -> Correct: coingecko and coincap route to CRYPTO
5. Twitter categories: []
   -> Twitter is stub (empty list), graceful handling expected
6. Sources for WEATHER: ['newsapi', 'reddit', 'open_meteo', 'openweathermap']
   -> open_meteo and openweathermap cover weather
7. Rate limit error class exists: NewsAPIBudgetExceeded
   -> Budget enforcement mechanism in place

VERDICT: All edge cases handled correctly
