feat(pi-overflow): 新增统一的新工具结果展示截断扩展

此前截断分散在多层且互相冲突：Pi bash 保留尾部 50KB，RTK 兜底截断又只留
开头 12000 字符（砍掉报错与完整输出路径），pi-chrome 截开头 30K，web_fetch
各 provider 不一致。新扩展统一负责"新结果给模型看多少"：
- capture.ts 最先加载暂存原文，index.ts 最后加载（system-prompt 之前）
- 超过 24K 字符时原文落盘 <agentDir>/my-pi/pi-overflow/（700/600、原子写），
  优先取 bash fullOutputPath 完整文件；模型看到 头 + 中段信号行 + 尾 的有界
  视图，行号基于落盘原文、结尾永远可见
- overflow_query：按 id 正则搜索、行区间、jsonPath 只读查询，id 校验防穿越
- 收编：RTK truncate 默认关闭、删除 pi-chrome truncateText、web_fetch 默认
  每页 20000（上限 100000）、web_search max_results 限定 1–20
- pi-compaction 遮蔽带 details.overflow.id 的结果时在占位符提示 overflow_query
- 登记 tools.jsonc / routing / 权限 allow / tool-search 常驻与分组

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tests/extension-load.test.ts

@@ -198,6 +198,21 @@ test("all package extensions load together without global registration conflicts
 		"./extensions/system-prompt.ts",
 		"the single system-prompt owner must be the last loaded extension",
 	);
+	// pi-overflow has two entry points with strict ordering: capture.ts must
+	// run first so it sees results before RTK rewrites them, and index.ts must
+	// run last (before system-prompt) so it bounds the final visible text.
+	assert.equal(
+		packageJson.pi.extensions.at(0),
+		"./pi-overflow/capture.ts",
+		"pi-overflow capture must be the first loaded extension",
+	);
+	assert.equal(packageJson.dependencies["pi-overflow"], "file:./pi-overflow");
+	assert.ok(filesIncludePackageDir(packageJson.files, "pi-overflow"), "the packed bundle must include pi-overflow source");
+	assert.equal(
+		packageJson.pi.extensions.at(-2),
+		"./pi-overflow/index.ts",
+		"pi-overflow bound stage must load after all other content extensions and before system-prompt",
+	);
 	assert.ok(
 		packageJson.pi.extensions.includes("./extensions/context-mode.ts"),
 		"Context Mode must load through the bundle's prompt-guarded wrapper",