Developer's AI agent silently corrupted its own 13KB memory file into 49MB over three days

A developer's autonomous agent, designed to wake every four hours and log its state to a file called STATUS.md, silently inflated that file from 13KB to nearly 49MB over three days due to a subtle Python bug. The flaw stemmed from inverted string indices causing a slice to return an empty string, which was then passed to Python's replace() method — inserting new content between every single character in the file. Because the corruption added rather than removed data, routine checks using grep and sed all passed, masking the problem entirely. The developer concluded that checking for content presence is structurally blind to dilution-style failures, and that coarse signals like file size can catch errors that precise content checks miss. As a fix, post-write size assertions, index-order validation, and structural checks on section headings were added to the agent's workflow.