## What changed
- Add `Platform` to `codex-utils-path-uri` with metadata parsing, native platform detection, and path convention mapping. Preserve missing or unrecognized metadata as `Unknown`.
- Replace `NetworkProxyExecutorOs` with the shared type and keep executor-specific socket path validation in the network proxy.
- Extract `effective_sandbox_mode` with explicit platform and Windows sandbox level inputs, preserving the native Windows fallback from `workspace-write` to `read-only` when the sandbox is disabled.
## Testing
Add unit tests for platform metadata, path conventions, native platform detection, and sandbox mode selection across platforms and Windows sandbox levels.
GitOrigin-RevId: 4fe0972e3a91040e35f2a6dfa5bcdf6c9a29be88