DeepSeek Harness Plugin: dsh-session-tree-extension — An Append-Only Multi-Branch Conversation Tree

The `dsh-session-tree-extension` plugin provides DeepSeek-Harness (DSH) with an append-only, multi-branch conversation tree structure, addressing the limitations of linear conversation history that are difficult to trace and modify. It allows users to fork and clone conversations at any historical node and manage lineage through the `/tree`, `/fork`, and `/clone` commands, with Git-style graph browsing supported in the WebUI. The plugin uses an immutable node design, remains compatible with multiple runtime modes, and requires no changes to Harness core files, making it well suited for development scenarios involving frequent debugging of historical branches.