An Hour Down Claude Code's Memory Hole

TL;DR: Claude Code ships an auto-memory feature on by default. It eats roughly 47% of every system prompt. One environment variable turns it off, and behavior improves immediately. The story below is what I saw and how I found the switch. Claude Code was acting off this week. Saving memories I didn't ask it to save. Taking verbose detours on simple tasks. Once, it edited a file without reading it first and guessed wrong about the contents. None of that was catastrophic. It was just friction. The kind that makes you wonder if the model got worse, or if you got dumber, or both.