## What changed
- Route filesystem helpers through `SandboxManager::transform`, moving helper policy preparation and Windows direct-spawn wrapping into the sandboxing crate.
- Require explicit workspace roots and an available sandbox for helper launches, restrict networking, and reject managed networking configuration.
- Share command preparation and integrity checks between helper requests and sandboxed file opens.
## Testing
Extend coverage for helper executable reads, workspace write boundaries, restricted networking, and Windows wrapper policy serialization. Verify that sandboxed writes to helper siblings leave host files unchanged.
GitOrigin-RevId: e57bfdabf47f79f2194b35df8a75051daf933465