There's a particular way an AI coding agent goes bad. Not a crash, not an error. It just gets duller. Halfway through a long session it forgets a constraint you set early, repeats a question you already answered, or starts giving you shorter, vaguer replies to the same kind of ask it handled well an hour ago. You can feel the quality sag without anything actually breaking.
My first instinct was to blame MCP. I had a few servers connected, I'd read that connected servers eat the context window, so the story wrote itself: too many tools loaded, no room left to think, of course it's drifting. I was about to start disconnecting things. Then I decided to measure first, and the measurement didn't say what I expected.
I read the breakdown instead of guessing
The agent I use can print a breakdown of what's currently filling the context window, by category. So before cutting anything, I looked at where the tokens were actually going. I'll give this in proportions rather than raw numbers, because the absolute figures depend on the model and window size, and the shape is the part that transfers.
Roughly, in a session that had started drifting:
