## Why
Unified exec could drop network approval registration when a selected environment used a Windows working directory on a non-Windows host because the trigger path could not be converted to a host absolute path.
## What changed
- Keep network approval trigger working directories as `PathUri` values and render them with their inferred native path syntax for Guardian requests.
- Fall back to the selected turn environment only when a trigger path can be converted to a host absolute path.
- Reject selected environment working directories larger than 8 KiB at the thread-manager validation boundary.
## Testing
- Cover managed-network approval registration for a foreign Windows working directory.
- Verify that oversized working directories are rejected as invalid `thread/start` requests.
GitOrigin-RevId: 646fbf12115a35a7e5cb04b511464797bee6647b
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