DeepSeek Harness (DSH) Extension: dsh-session-summarizer

The native DSH ecosystem plugin `dsh-session-summarizer` is designed to address context loss in long conversations. It does not rely on external services and uses the official DSH runtime to read sessions and generate Chinese summaries, helping models quickly recover context. The plugin can be invoked via the `session_summarize` tool, allowing users to specify a session ID and the number of turns to summarize. Its transcription strategy retains the beginning and end while truncating the middle, with a default budget of 12,000 characters. After installation, models can directly call this tool to manage session summaries.