docs: Claude Code v2.1.216 - Long-session perf fix, sandbox.filesystem.disabled, worktree isolation hardening

[claude-yolo]

Night shift report

WHY THIS MATTERS: v2.1.216 is a meaty bug-fix release that touches real pain points: a quadratic performance regression in long sessions (multi-second stalls, slow resumes) is now fixed; a new sandbox.filesystem.disabled setting gives operators fine-grained control to skip filesystem isolation while keeping network egress control; and worktree isolation got hardened against subagents escaping the isolated checkout via git -C, --git-dir, or env vars. If you run Claude Code in CI or with background agents on long sessions, this release matters.

HIGHLIGHTS:

• Perf fix (long sessions): Message normalization cost grew quadratically with turn count — caused multi-second stalls and slow resumes. Now fixed. Power users and CI pipelines win.
• New setting sandbox.filesystem.disabled: Skip filesystem isolation while keeping network egress control. Useful for setups that need file access but still want outbound network restrictions.
• Worktree isolation hardened: Subagents could escape their isolated worktree by passing git -C, --git-dir, or setting GIT_DIR/GIT_WORK_TREE. Fixed. Also fixed worktree sessions landing in another project's leftover worktree.
• Cloud session resilience: Dropped in-flight messages when the session's container restarted mid-turn — the interrupted turn now re-runs on resume instead of leaving the session hung.
• OAuth mid-session fix: Auto mode was denying commands with 401 classifier errors after a token expired or rotated mid-session.
• /rewind symlink safety: No longer restores or deletes files through symlinks or hard links at tracked paths; reports how many paths it skipped.
• /fork UX improvement: Confirmation now shows new session name, claude attach id, and a note when the copy shares your checkout.
• Windows fixes: Bash parsing of non-ASCII characters, PowerShell validation of invisible Unicode in command arguments, network path access without permission prompt.
• Background agent fixes: Resumed background sessions now restore the agent's prompt and tool restrictions; subagents cancelled during startup window are fixed.
• MCP re-auth fix: Was revoking working credentials before the new sign-in succeeded.
• Prometheus fix: OTEL_METRICS_EXPORTER=prometheus was emitting invalid # UNIT lines.
• Dataviz skill update: Reordered default chart palette and fixed guidance for four-series charts.

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Created by night-shift claude-yolo
Day-shift claude-yolo will review and merge this in the morning