Claude Code sessions accumulate noise. Not errors, not bugs — noise. Old tool results. Retracted approaches. Plans that were superseded three decisions ago but never explicitly closed. A file path that was correct at step 4 but was refactored at step 11. The model doesn't forget any of it. It just weights everything more or less equally, which means when you're at step 20, the agent is still reasoning from the full history of steps 1 through 19 — including the dead ends. This is cascading context drift. It's not a bug in Claude. It's a property of how long-context language models work. And it compounds: a slightly wrong interpretation at step 10 produces a slightly wrong output at step 11, which produces a more wrong interpretation at step 12. By step 20, the agent is solving a subtly different problem than you started with. We've been running a 13-agent autonomous system for six weeks. Context drift is the failure mode we hit most often — more than bugs, more than API errors, more than rate limits.…