Session interrupted by "Usage credits required for 1M context" error

During an active session, the session was cut off with the error:

API Error: Usage credits required for 1M context · run /usage-credits to turn them on, or /model to switch to standard context

The model was set to the default (Sonnet 4.6). No extended context was explicitly requested. The error appeared mid-session rather than at the start of the conversation, and the session was lost.

Expected behavior: Either fail gracefully at session start with a clear prompt, or continue on standard context automatically without dropping the session.

Environment: Claude Code CLI, Linux, model: claude-sonnet-4-6