DeepSeek Harness Plugin: @vidge/dsh-omniloop Multi-Engine Routing

The `@vidge/dsh-omniloop` plugin refactors the single `AgentFactory` in DeepSeek Harness (DSH) into a router, enabling multiple agent engines—such as Claude Code, Codex, and Pi—to run within the same DSH instance. Core features include session-level routing, runtime switching, shared infrastructure, and output translation. Users need to install the plugin and the corresponding SDKs via the command line, then select the desired engine in Composer. This solution enables multi-engine coexistence, maintains session state consistency, and supports persistent affinity.