Policy File Resilience: EBUSY Fallback and TOML Recovery

What Changed

Enhanced policy file persistence with EBUSY/EXDEV fallback mechanism and TOML parse recovery. When atomic rename fails on certain mount configs, falls back to copy-then-unlink. If policy file becomes corrupted with syntax errors, automatically backs up malformed file with .bak extension and recovers from scratch.

Operator Implication

Prevents policy update failures in cross-device mount scenarios common in containerized environments. Automatic corrupted file recovery eliminates manual intervention for syntax errors. Improves resilience of configuration persistence layer.

Receipt

• Commit title: 'fix(policy): add EBUSY fallback and TOML parse recovery (#19919) (#21541)' with 51 additions and 8 deletions to packages/core/src/policy/config.t