Managed disk directories for extensions needing real filesystem access
(git, compilers, media tools). Five builtins: create, path, list,
delete, usage. Extension-scoped to {WORKSPACE_ROOT}/{packageID}/{name}/.
- New sandbox/workspace_module.go with path traversal + symlink protection
- Permission: workspace.manage; config: WORKSPACE_ROOT, WORKSPACE_QUOTA_MB
- Runner wiring with graceful degradation (module absent if root unwritable)
- 16 new tests, all passing with -race
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
