## Why
Older executors sandbox reads whenever a policy is supplied, even when the policy allows unrestricted reads. This can interfere with loading skills across executor versions.
## What changed
- Omit sandbox contexts from remote read operations when reads are unrestricted and explicit permission paths are valid for the target path convention. Retain contexts that require executor-side path validation.
- Check remote `windows_mxc` support before sending MXC sandbox contexts for reads or capability discovery, returning an update-executor error when unsupported.
## Testing
Add coverage for permission path validation across read operations, unsupported MXC requests, and skill loading over Noise with mismatched app and executor versions, including selected skill roots with capability discovery disabled.
GitOrigin-RevId: 4a2a7ccaa2ba4daac657bd84aea603404452be45
## What changed
- Accept `windows.sandbox = "mxc"` and preserve the selected backend through environment configuration, command execution, patch writes, and sandbox metadata.
- Treat MXC as enabled in the TUI and report Windows sandbox readiness as `ready`, avoiding legacy setup prompts.
- Keep `allowed_sandbox_implementations` scoped to the legacy elevated and unelevated backends without restricting MXC.
- Default `windows.sandbox_private_desktop` to `false` for MXC while retaining `true` for legacy sandboxes.
## Testing
Add coverage for MXC configuration precedence, legacy requirement handling, sandbox selection, and TUI state. Add a Wine integration test that verifies command and patch routing fails when native MXC is unavailable and reports `windows_mxc` in turn metadata.
GitOrigin-RevId: e2162447d0750f60753864c92a20e02a7f297bca
## Why
MXC is a sandbox implementation, not a restricted-token sandbox level. Executor requests need to represent that choice separately from `WindowsSandboxLevel`.
## What changed
- Introduce `WindowsSandboxSelection` for executor sandbox contexts and remove `Mxc` from `WindowsSandboxLevel`.
- Preserve the `windowsSandboxLevel` wire field and its serialized values for compatibility.
- Share sandbox selection between executor process launches and filesystem helpers, and use the new selection in capability discovery and skill reads.
- Disable Windows sandbox selection for executor paths that do not use Windows path conventions.
## Testing
Extend coverage for MXC wire serialization, Windows skill-read sandbox checks, and capability discovery with distinct permissions. Exercise remote filesystem write restrictions with both restricted-token and MXC sandboxes, including rejection when native MXC is unavailable.
GitOrigin-RevId: 266211377bcb138a0dc75861e9ff2225fa37a53d
Dmitriy Kovalenko