dsh-message-handoff: DeepSeek Harness Message-Level Conversation Handoff Plugin

`dsh-message-handoff` is a plugin for DeepSeek Harness designed to address the issue of the Fork feature breaking context continuity. By providing a “handoff” handle next to assistant messages, it enables message-level session forking: copying the history before that message and using an LLM to summarize the content after it, thereby generating a new session with structured documentation such as task goals and progress. The plugin has no dependencies, is easy to install, and supports configurable input and output limits. Developers can click the Handoff icon to automatically create and open a sub-session with full context, greatly facilitating complex development scenarios that require continuing a conversation from an intermediate point.