feat(prompt): 重新注册 bash，把"不要用 bash 搜索"写进工具描述

真实会话里模型仍习惯性先调 bash grep，被拒后才改用 grep 工具；系统提示词里已有 4 处
提醒，但模型下调用决定时看的是工具 schema 描述，而 Pi 内置 bash 描述对此只字未提。

- 新增 extensions/bash-override.ts：用 Pi 的 createBashToolDefinition 重新注册 bash，
  执行、输出结构与 codemode 说明完全沿用上游；shellPath/commandPrefix 按 ctx.cwd
  经 SettingsManager 惰性解析，与内置一致
- tools.jsonc 新增 descriptionAppend 字段，由 prompt-guard 注册时拼接到上游描述后
- bash 增加命令→工具对照规则（grep -n / grep -rl / find -name），并提示
  文件清单用 $(git ls-files) 传参、不要接 xargs（会触发权限审核）

Generated with [Devin](https://devin.ai)

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

extensions/prompt-guard.ts

@@ -1,11 +1,28 @@
 import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
 
-import { loadToolCatalog, type ToolCatalog } from "./system-prompt-config.ts";
+import {
+	loadToolCatalog,
+	type ToolCatalog,
+	type ToolCatalogEntry,
+} from "./system-prompt-config.ts";
 
 type AnyMessage = { role?: string; content?: unknown } & Record<string, unknown>;
 
 type AnyHandler = (event: never, ctx: never) => unknown;
 
+/**
+ * The description a tool registers with under its catalog entry: a `description`
+ * override replaces the upstream text, a `descriptionAppend` is joined onto
+ * whichever base wins (override first, upstream otherwise) with a blank line.
+ */
+export function catalogDescription(description: string, entry: ToolCatalogEntry): string {
+	if ("inherit" in entry) return description;
+	const base = typeof entry.description === "string" ? entry.description : description;
+	return typeof entry.descriptionAppend === "string"
+		? `${base.trimEnd()}\n\n${entry.descriptionAppend}`
+		: base;
+}
+
 export interface PromptGuardOptions {
 	/**
 	 * Post-process the messages a wrapped `context` handler leaves behind.
@@ -19,9 +36,11 @@ export interface PromptGuardOptions {
  * Proxy an `ExtensionAPI` for third-party extensions so they cannot bypass the
  * bundle's single system-prompt owner (`extensions/system-prompt.ts`):
  *
- * - `registerTool` applies the tool's `description` override from
- *   `config/prompt/tools.jsonc` when the catalog carries one (lazily loaded;
- *   a catalog error keeps the upstream description).
+ * - `registerTool` applies the tool's `description` override and
+ *   `descriptionAppend` suffix from `config/prompt/tools.jsonc` when the
+ *   catalog carries them (lazily loaded; a catalog error keeps the upstream
+ *   description). An append composes onto the override when both are set, or
+ *   onto the upstream description when only the append is set.
  * - `before_agent_start` handlers keep every returned field except
  *   `systemPrompt`, which is dropped.
  * - `context` handlers are post-processed through `opts.contextFilter`.
@@ -42,10 +61,12 @@ export function guardExtensionApi(pi: ExtensionAPI, opts: PromptGuardOptions = {
 
 	const registerTool: ExtensionAPI["registerTool"] = (tool) => {
 		const entry = catalog()?.tools[tool.name];
-		if (entry !== undefined && !("inherit" in entry) && typeof entry.description === "string") {
-			pi.registerTool({ ...tool, description: entry.description });
-		} else {
+		const description =
+			entry === undefined ? tool.description : catalogDescription(tool.description, entry);
+		if (description === tool.description) {
 			pi.registerTool(tool);
+		} else {
+			pi.registerTool({ ...tool, description });
 		}
 	};