One Bad Argument, Forever

During an autonomous coding session, the model generated a tool call whose arguments were truncated, invalid JSON, an unterminated string. The system's error handling caught the malformed call but, rather than discarding it, stored the broken argument text as-is in the conversation history used for future turns. From that point on, every subsequent turn resent the same corrupted arguments back to the model provider, which rejected the request every time; the session was permanently stuck and required a manual reset to recover.

A one-off generation glitch with no lasting effect, considered and ruled out. A single malformed call is unsurprising on its own, but the session did not recover from it the way a normal transient error would; the broken call persisted in memory and kept breaking every later turn.

Perseveration (repeating a failing action without adapting), considered, since the symptom was a repeating failure. Ruled out as the primary cause because the repetition here wasn't the model retrying a choice, it was the surrounding system re-transmitting a corrupted record it never should have kept in the first place.

Apraxia, most consistent with the evidence. The mechanics of handling a malformed tool call broke down: invalid arguments weren't validated before being sent, and once they failed, they were preserved in history rather than sanitized, poisoning every call that followed.

The failure here isn't that a model occasionally produces malformed output (that will always happen sometimes) it's that the system had no way to quarantine the bad output once it appeared, so one truncated string turned into a permanently broken session. Validating tool-call arguments against their schema before they're sent, and stripping anything that fails validation out of the conversation record rather than storing it, is the kind of unglamorous plumbing that keeps a single bad call from cascading.

Validate tool-call arguments against their schema before sending, and strip failures from the conversation record.

Schema validation; quarantine of invalid output; session recovery without manual reset.