Turn nine of a support chat feels fine. Turn ninety is a different animal. Every request resends the system prompt, three agent loops of tool noise, the user's third restatement of the same bug, and yesterday's dark-mode tangent. The model does not mind. Your invoice does — and attention quality usually dies before the hard token limit. messages.TakeLast(20) in one controller is not a policy. The second entry point forgets it. A tool-using agent keeps a function call without its result. Som...