Claude Code version 2.1.216 addresses a critical performance regression where message normalization cost grew quadratically with the number of turns, causing multi-second stalls in long sessions. The update also introduces a new `sandbox.filesystem.disabled` setting that allows users to skip filesystem isolation while retaining network egress control.
- Fixed auto mode denying commands with HTTP 401 errors after OAuth token expiration or rotation.
- Resolved issues with resumed background agent sessions reverting to the default agent by restoring prompt and tool restrictions.
- Corrected Bash command parsing for non-ASCII characters and PowerShell permission validation for invisible Unicode.
- Improved `/ultrareview` and `/code-review ultra` error messages to display configured limits and base refs.
- Fixed cloud sessions dropping in-flight messages during container restarts by re-running interrupted turns on resume.
These changes improve stability in long-running workflows, enhance security configuration options, and ensure accurate command parsing across different shell environments.