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

pi-web-search/index.ts

@@ -21,8 +21,15 @@ import {
 } from "./router.ts";
 
 const DEFAULT_MAX_RESULTS = 8;
+const MAX_RESULTS_LIMIT = 20;
 const MAX_FETCH_URLS = 10;
-const DEFAULT_FETCH_MAX_CHARACTERS = 3000;
+const DEFAULT_FETCH_MAX_CHARACTERS = 20000;
+const FETCH_MAX_CHARACTERS_LIMIT = 100000;
+
+function clampInt(value: number | undefined, fallback: number, min: number, max: number): number {
+	if (typeof value !== "number" || !Number.isFinite(value)) return fallback;
+	return Math.min(Math.max(Math.floor(value), min), max);
+}
 
 export interface WebSearchParams {
 	query: string;
@@ -48,7 +55,7 @@ function formatSearchPayload(payload: unknown): string {
 export function toTavilyParams(params: WebSearchParams) {
 	return {
 		query: params.query,
-		max_results: params.max_results ?? DEFAULT_MAX_RESULTS,
+		max_results: clampInt(params.max_results, DEFAULT_MAX_RESULTS, 1, MAX_RESULTS_LIMIT),
 		search_depth: (params.depth ?? "basic") as "basic" | "advanced",
 		include_domains: params.site ? [params.site] : undefined,
 		start_date: params.published_after,
@@ -59,7 +66,7 @@ export function toTavilyParams(params: WebSearchParams) {
 export function toExaParams(params: WebSearchParams) {
 	return {
 		query: params.query,
-		numResults: params.max_results ?? DEFAULT_MAX_RESULTS,
+		numResults: clampInt(params.max_results, DEFAULT_MAX_RESULTS, 1, MAX_RESULTS_LIMIT),
 		includeDomains: params.site ? [params.site] : undefined,
 		startPublishedDate: params.published_after,
 		endPublishedDate: params.published_before,
@@ -171,7 +178,7 @@ export async function dispatchFetch(
 	if (urls.length > MAX_FETCH_URLS) {
 		return toResult(`web_fetch accepts at most ${MAX_FETCH_URLS} URLs per call; received ${urls.length}.`, { error: true });
 	}
-	const maxCharacters = params.max_characters ?? DEFAULT_FETCH_MAX_CHARACTERS;
+	const maxCharacters = clampInt(params.max_characters, DEFAULT_FETCH_MAX_CHARACTERS, 1, FETCH_MAX_CHARACTERS_LIMIT);
 	const order: SearchProvider[] = ["exa", "keenable"];
 	if (tavilyAvailable(resolve)) order.push("tavily");
 
@@ -213,7 +220,9 @@ export default function webSearchExtension(pi: ExtensionAPI): void {
 				},
 				max_results: {
 					type: "number",
-					description: `Maximum number of results to return (default ${DEFAULT_MAX_RESULTS}).`,
+					minimum: 1,
+					maximum: MAX_RESULTS_LIMIT,
+					description: `Maximum number of results to return (default ${DEFAULT_MAX_RESULTS}, max ${MAX_RESULTS_LIMIT}).`,
 				},
 				site: {
 					type: "string",
@@ -268,7 +277,9 @@ export default function webSearchExtension(pi: ExtensionAPI): void {
 				},
 				max_characters: {
 					type: "number",
-					description: `Maximum characters to extract per page (default ${DEFAULT_FETCH_MAX_CHARACTERS}).`,
+					minimum: 1,
+					maximum: FETCH_MAX_CHARACTERS_LIMIT,
+					description: `Maximum characters to extract per page (default ${DEFAULT_FETCH_MAX_CHARACTERS}, max ${FETCH_MAX_CHARACTERS_LIMIT}).`,
 				},
 			},
 			required: ["urls"],