dsh-plumb-identity: Proxy-Level Plumb Session Identity for DeepSeek Harness

The MCP client of DSH Harness (DSH) does not send identity information, causing the Plumb isolation layer to fail to correctly distinguish conversations and leading to workspace lock conflicts. The `dsh-plumb-identity` plugin resolves this by providing a stable transport-layer identity for each DSH conversation, workspace, and subagent. It supports installation via a Bundle or manual patch configuration, defaults to the `plumb` server, and supports flexible configuration options. After installation, restart the DSH process and watch for version compatibility and installation conflicts.