An agent monitoring 100 data streams degrades after 6 hours: early alerts are missed while recent ones are handled correctly. The most likely cause is:
Answer: The agent's context window has filled with recent alerts, pushing early context out of attention
The symptom — early events missed, recent events handled — is the signature of context window saturation (B). When the context fills, older content receives less attention than recent content. Rate limits (A) affect all events equally. Malformed data (C) would cause tool errors. Token expiry (D) would cause auth failures, not selective context loss.