A hook that halts a Claude Code session when the model serving it changes mid-session β for example when Fable 5 falls back to Opus 4.8 because credits ran out or a safety classifier flagged a request.
Without this, a session can silently continue for tens of minutes on a model you did not choose. In the case that prompted this, a session ran 309 messages on Fable 5, switched at the 310th, and continued for 91 more messages over 30 minutes before anyone noticed.