kv-cache 2

Context compression tool (context_compact): the agent writes the replacement checkpoint itself and hands it to the host compaction engine, which skips the LLM summarizer call; automatic compaction stays on the official engine.

Deterministic system-prompt section ordering for DeepSeek Harness — fixes KV-cache invalidation from unstable same-order section ordering across session resume. / 确定性 system-prompt section 排序：修复会话恢复时同 order section 排序漂移导致的 KV 缓存断层。