Dsh Session Header

Key features

• the llm/stream waterfall names the calls that are LLM calls and carries options.sessionId
• The llm-deepseek adapter already sends its own x-deepseek-harness-session-id on every request
• a globalThis.fetch patch adds the header, so every fetch-based adapter (llm-deepseek, llm-pi-ai, and any SDK whose transport bottoms out in global fetch) is covered without touching adapter code.
• value configa fixed value for every call instead (sent verbatim, no prefix stripping)
• calls with neither get no header.