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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pi-overflow/capture.ts

@@ -0,0 +1,30 @@
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
+import { readOverflowSettings } from "./settings.ts";
+import { getStash, stashResult } from "./src/stash.ts";
+
+/**
+ * Pre-bound capture: loaded FIRST in pi.extensions, before RTK or any other
+ * result-rewriting extension. It only stashes the untouched original text —
+ * it never modifies the result. The bound stage (`index.ts`, loaded last)
+ * consumes the stash after all other handlers have run.
+ */
+export default function overflowCapture(pi: ExtensionAPI): void {
+	const settings = readOverflowSettings();
+	pi.on("tool_result", (event) => {
+		if (!settings.enabled) return undefined;
+		if (settings.exemptTools.includes(event.toolName)) return undefined;
+		if (event.parentToolCallId) return undefined;
+		const rawText = event.content
+			.filter((part): part is { type: "text"; text: string } => part.type === "text")
+			.map((part) => part.text)
+			.join("\n");
+		const fullOutputPath =
+			typeof event.details?.fullOutputPath === "string" ? event.details.fullOutputPath : undefined;
+		if (rawText.length <= settings.thresholdChars && !fullOutputPath) return undefined;
+		stashResult(getStash(), event.toolCallId, {
+			rawText,
+			...(fullOutputPath ? { fullOutputPath } : {}),
+		});
+		return undefined;
+	});
+}