refactor(pi-compaction): 改为压力触发的观察遮蔽与空闲阈值整段摘要

原实现对所有工具结果（含 read）在下一次请求即替换为约 4K 的首尾存根，
不看上下文压力，导致模型看不到大文件中段；后台逐条语义摘要又反复改写
历史、打碎 prompt 缓存。参照 Anthropic 上下文编辑、Manus 与 JetBrains
观察遮蔽研究重构为：
- L2：上下文达到阈值时在 turn_end 批量提交 Pi 原生 context_edit，把最近
  keepRecentTurns 轮之外的旧 toolResult 换成确定性占位符；trigger/target
  回差与 minClearTokens 保证少触发、一次清够；原始条目保留，可经
  context_tree_query 取回
- L3：空闲 agent_settled 且超过绝对阈值时调用一次 ctx.compact
- 阈值按绝对 token 计并受窗口比例约束，默认针对 1M 窗口（DeepSeek V4.1
  Flash）：遮蔽 200K→100K、整段摘要 400K
- 删除逐条存根、语义 worker、soft/hard/target 比例与自行取消 Pi 压缩的门控；
  Pi 原生阈值压缩保留为最终安全网

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

pi-compaction/test/performance.test.ts

@@ -10,9 +10,9 @@ function message(index: number) {
 
 test("cached projection and append-only delta stay inside the hot-path budget", () => {
   const index = new SegmentIndex("perf");
-  index.hydrate([], DEFAULT_CONFIG);
+  index.hydrate();
   const messages = Array.from({ length: 10_000 }, (_, value) => message(value));
-  const params = { environmentHash: "env", environmentTokens: 2_000, contextWindow: 300_000 };
+  const params = { environmentHash: "env", environmentTokens: 2_000, contextWindow: 300_000, maskedResults: 0, reclaimedTokens: 0 };
   index.project(messages, params);
 
   const cacheStart = performance.now();
@@ -24,6 +24,7 @@ test("cached projection and append-only delta stay inside the hot-path budget",
   index.project(appended, params);
   const deltaMs = performance.now() - deltaStart;
 
+  console.log(`cache-hit average ${cacheAverageMs.toFixed(3)}ms; delta projection ${deltaMs.toFixed(3)}ms`);
   assert.ok(cacheAverageMs < 2, `cache-hit average ${cacheAverageMs.toFixed(3)}ms exceeded 2ms`);
   assert.ok(deltaMs < 10, `delta projection ${deltaMs.toFixed(3)}ms exceeded 10ms`);
 });