DeepSeek Harness (DSH) Plugin: dsh-wsl

The `dsh-wsl` plugin enables the DeepSeek Harness (DSH) model agent to execute Linux commands directly through `wsl.exe`, without requiring script-based wrappers. It registers three core tools: `wsl` (command execution, including long scripts and background jobs), `wsl-path` (Windows-to-Linux path conversion), and `wsl-env` (environment detection). Installation should be performed via the plugin manager, and background jobs depend on specific presets. The plugin runs under the DSH sandbox and is constrained by Windows driver filesystem semantics.