DeepSeek Harness plug-in that inserts custom prompts

Key features

• The reference exchanges are built once at plugin activation into alternating real Message objects (deep-frozen, shared by reference across requests), then prepended onto every ordinary conversation request by an llm/stream waterfall listener
• Customizingnever copy a - insert: row.
• Clone and redispatchloop-built requests are deep-frozen and marker-tagged (markAgentLoopRequest(deepFreeze(...))) and never mutated
• the listener clones the request, prepends the seed messages, and redispatches through ctx.llm.stream.
• The clone carries no loop marker, the agent-loop log-reconstruction invariant does not apply to it, and the discarded original is a pure deriveMessages() projection.