diff --git a/AGENTS.md b/AGENTS.md
index 1ec57bf..a565197 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -21,6 +21,7 @@
 | `pi-compaction/` | 压力触发的观察遮蔽（Pi context_edit）、阈值整段摘要、effective token、native compaction |
 | `pi-overflow/` | 新工具结果统一截断：超阈值原文落盘 + 有界视图 + `overflow_query` |
 | `extensions/fff-override.ts` | FFF `override` 模式接管 `find`/`grep` 与 `@` 补全，`multi_grep` 按上游保持关闭 |
+| `extensions/bash-override.ts` | 用 Pi 的 `createBashToolDefinition` 重新注册 `bash`，仅替换模型可见描述（追加 `tools.jsonc` `descriptionAppend`）；执行逻辑、输出结构、codemode 说明不变 |
 | `extensions/codegraph.ts` | 原生 `codegraph_explore`，自有 stdio JSON-RPC 直连 `codegraph serve`（`codegraph-client.ts`） |
 | `extensions/hashline.ts` | 部署 `config/pi-hashline-edit.json` 后加载 pi-hashline-edit 覆盖 `read`/`edit`（`hashline-config.ts`） |
 | `extensions/permission-system.ts` | 直接加载仓库内 `pi-permission-system/src/index.ts` |
diff --git a/README.md b/README.md
index 5691605..68c94bb 100644
--- a/README.md
+++ b/README.md
@@ -215,6 +215,10 @@ Pi 的 `find` 和 `grep`；`multi_grep` 上游标注为有害、默认关闭，w
 删除 `PI_FFF_MULTIGREP` 环境变量，使其永远无法注册。RTK 对所有 `grep` 工具结果直接跳过，
 也默认关闭 Bash 命令改写，因此不会把 `rg`、`grep`、`find` 或 `fd` 改写到 RTK。
 
+`extensions/bash-override.ts` 用 Pi 的 `createBashToolDefinition` 重新注册内置 `bash`，
+把「不要用 bash 搜索」的警告经 `tools.jsonc` 的 `descriptionAppend` 写进工具 schema，
+让模型在调用时就看到替代工具；执行逻辑、输出结构和 codemode 的 `tools.bash` 说明完全沿用上游定义。
+
 ### 输出压缩归 RTK
 
 RTK 保留 Bash、read、build、test、lint 和 Git 输出压缩。默认 `read` 的有损压缩
diff --git a/config/prompt/routing.jsonc b/config/prompt/routing.jsonc
index f66fe60..7e64ded 100644
--- a/config/prompt/routing.jsonc
+++ b/config/prompt/routing.jsonc
@@ -30,7 +30,7 @@
     },
     {
       "whenAny": ["bash"],
-      "text": "Use bash for builds, tests, git, package scripts, and other programs. Never run grep, rg, find, fd, or git grep in bash — standalone, piped, inside a loop, or in $(…). Search files with the grep/find tools; when a program needs a file list (wc, node, tsc), pass $(git ls-files '<glob>')."
+      "text": "Use bash for builds, tests, git, package scripts, and other programs. Never run grep, rg, find, fd, or git grep in bash — standalone, piped, inside a loop, or in $(…). Search files with the grep/find tools; when a program needs a file list (wc, node, tsc), pass $(git ls-files '<glob>') as arguments rather than piping into xargs."
     },
     {
       "whenAll": ["bash", "overflow_query"],
diff --git a/config/prompt/tools.jsonc b/config/prompt/tools.jsonc
index 165ea1a..1180f89 100644
--- a/config/prompt/tools.jsonc
+++ b/config/prompt/tools.jsonc
@@ -2,17 +2,26 @@
   // Bundle-authoritative tool guidance, owned by extensions/system-prompt.ts.
   //
   // Every tool the bundle can expose must have an entry. Per field:
-  //   "snippet"     — replaces the tool's one-line <tools> entry (null hides it)
-  //   "guidelines"  — replaces the tool's <rules> lines
-  //   "description" — replaces the tool description at registration; only
-  //                   applied to third-party tools loaded through a bundle
-  //                   adapter (in-repo tools edit their own source instead)
+  //   "snippet"           — replaces the tool's one-line <tools> entry (null hides it)
+  //   "guidelines"        — replaces the tool's <rules> lines
+  //   "description"       — replaces the tool description at registration
+  //   "descriptionAppend" — appended to the description at registration (on top
+  //                         of "description" when both are set)
+  // "description"/"descriptionAppend" only apply to tools registered through a
+  // bundle adapter (prompt-guard), which includes the bash override and the
+  // third-party wrappers; other in-repo tools edit their own source instead.
   // An absent field keeps the upstream text. "inherit": true means the
   // upstream text was reviewed against this bundle and is kept as-is.
   "version": 1,
   "tools": {
     "bash": {
-      "snippet": "Run shell commands for builds, tests, git, package scripts, and other programs; search files with the find/grep tools, not bash"
+      "snippet": "Run shell commands for builds, tests, git, package scripts, and other programs; search files with the find/grep tools, not bash",
+      "descriptionAppend": "Not for searching files: use the grep tool for file contents and the find tool for paths (e.g. `grep -n X src/*.ts` → grep {pattern: \"X\", path: \"src/*.ts\"}); grep, rg, find, fd, and git grep are denied here. When a program needs many files, pass $(git ls-files '<glob>') as arguments instead of piping into xargs, which triggers a permission review.",
+      "guidelines": [
+        "You can inspect PI_* environment variables for current model and session details.",
+        "Search commands are denied in bash; call the tools instead: `grep -n X src/*.ts` → grep {pattern: \"X\", path: \"src/*.ts\"}; `grep -rl X src` → grep {pattern: \"X\", path: \"src/\"} and take the file names; `find . -name '*.ts'` → find {pattern: \"\", path: \"**/*.ts\"}.",
+        "When a program needs many files (wc, node, tsc), pass $(git ls-files '<glob>') as arguments; piping into xargs triggers a permission review."
+      ]
     },
     "read": { "inherit": true },
     "edit": {
diff --git a/extensions/AGENTS.md b/extensions/AGENTS.md
index 7eff582..ce3a179 100644
--- a/extensions/AGENTS.md
+++ b/extensions/AGENTS.md
@@ -25,6 +25,7 @@
 ## 各 wrapper 约定
 
 - `fff-override.ts`：强制 FFF 官方 `override` 模式，统一接管 `find`、`grep` 和 `@` 补全；`multi_grep` 按上游保持关闭（加载前删除 `PI_FFF_MULTIGREP` 环境变量）。FFF 独占本地字面搜索，远端服务器搜索由 `ssh_find` / `ssh_grep` 负责，RTK 不得接管搜索工具（见 `pi-rtk-optimizer/AGENTS.md`）。显式 CLI flag 仍遵循 FFF 官方优先级。
+- `bash-override.ts`：用 `createBashToolDefinition` 重新注册内置 `bash`，目的只是让 `tools.jsonc` 的 `descriptionAppend` 落到模型可见描述里（prompt-guard 在注册时拼接）。ExtensionContext 不暴露 session settings，因此 `shellPath`/`commandPrefix` 在首次 execute 时按 `ctx.cwd` 经 `SettingsManager.create(ctx.cwd, getAgentDir())` 惰性解析并按 cwd 缓存，metadata 来自 `process.cwd()` 的定义；执行、输出结构与 codemode 说明完全委托上游定义，不得改动上游执行逻辑，也不得用 prepareLoadout 或 provider-payload 改写实现同样效果。
 - `codegraph.ts` + `codegraph-client.ts`：注册原生 `codegraph_explore` 工具，按索引根惰性常驻 `codegraph serve --mcp -p <root>` 子进程，经组合包自有 stdio 逐行 JSON-RPC 客户端直连（不经 shell、不带 pi-mcp-adapter 或 MCP SDK）；serve 进程内置文件监听自动同步索引，无结果缓存。子进程 10 分钟无调用自动关闭、会话结束统一关闭；调用中死亡换新客户端透明重试一次；其启动的上游 daemon（`.codegraph/daemon.sock`）退出后可多驻留 ≤5 分钟，属上游行为，组合包不管理。
 - CodeGraph 是机器级依赖，`install.sh`/`update.sh` 经官方安装器管理 `codegraph` CLI，组合包不内置其运行时。安装、升级和普通启动流程不得执行 `codegraph init`；只有 `codegraph_explore` 在未初始化项目上被调用、且用户在 `ctx.ui.confirm` 中明确确认后才可 `codegraph init` 当前目录，拒绝记入会话级 declined 不再重复询问；init 失败必须如实报告并让模型回退内置工具；不得改动 CodeGraph 更新或遥测设置。CLI 缺失、init 被拒或服务调用失败都不得抛出，必须以文本结果打回并引导模型改用 `find`/`grep`/`read`/LSP。已移除的 `plugin-init.ts`（原 `/plugin_init`）职责已并入本文件的惰性确认，不得恢复。
 - `hashline.ts` + `hashline-config.ts`：部署组合包权威 `config/pi-hashline-edit.json` 后加载 `pi-hashline-edit`；默认以 2 字符行哈希覆盖内置 `read` / `edit`，`grep` 与 `replaceText` 均关闭。它保证锚定编辑而不负责压缩，大文件上下文节省必须来自先定位/隔离分析、再做最小范围 `offset/limit` 读取。
diff --git a/extensions/bash-override.ts b/extensions/bash-override.ts
new file mode 100644
index 0000000..596c77c
--- /dev/null
+++ b/extensions/bash-override.ts
@@ -0,0 +1,38 @@
+import {
+	createBashToolDefinition,
+	type ExtensionAPI,
+	getAgentDir,
+	SettingsManager,
+} from "@earendil-works/pi-coding-agent";
+import { guardExtensionApi } from "./prompt-guard.ts";
+
+type BashDefinition = ReturnType<typeof createBashToolDefinition>;
+
+/** Re-register Pi's bash so tools.jsonc can append to its model-facing description; execution stays upstream. */
+export default function bashOverrideExtension(pi: ExtensionAPI): void {
+	const sessionDefinitions = new Map<string, BashDefinition>();
+	const sessionDefinition = (cwd: string): BashDefinition => {
+		let definition = sessionDefinitions.get(cwd);
+		if (definition === undefined) {
+			const settings = SettingsManager.create(cwd, getAgentDir());
+			definition = createBashToolDefinition(cwd, {
+				shellPath: settings.getShellPath(),
+				commandPrefix: settings.getShellCommandPrefix(),
+			});
+			sessionDefinitions.set(cwd, definition);
+		}
+		return definition;
+	};
+
+	guardExtensionApi(pi).registerTool({
+		...sessionDefinition(process.cwd()),
+		execute: (toolCallId, params, signal, onUpdate, ctx) =>
+			sessionDefinition(ctx?.cwd ?? process.cwd()).execute(
+				toolCallId,
+				params,
+				signal,
+				onUpdate,
+				ctx,
+			),
+	});
+}
diff --git a/extensions/prompt-guard.ts b/extensions/prompt-guard.ts
index 7c174c9..14c39d6 100644
--- a/extensions/prompt-guard.ts
+++ b/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 });
 		}
 	};
 
diff --git a/extensions/system-prompt-config.ts b/extensions/system-prompt-config.ts
index dbf171e..bd72f80 100644
--- a/extensions/system-prompt-config.ts
+++ b/extensions/system-prompt-config.ts
@@ -10,7 +10,12 @@ import { fileURLToPath } from "node:url";
 /** Entry in `config/prompt/tools.jsonc`. */
 export type ToolCatalogEntry =
 	| { inherit: true }
-	| { snippet?: string | null; guidelines?: string[]; description?: string };
+	| {
+			snippet?: string | null;
+			guidelines?: string[];
+			description?: string;
+			descriptionAppend?: string;
+	  };
 
 export interface ToolCatalog {
 	version: 1;
@@ -152,7 +157,7 @@ function isStringArray(value: unknown): value is string[] {
 	return Array.isArray(value) && value.every((entry) => typeof entry === "string");
 }
 
-const TOOL_ENTRY_KEYS = new Set(["inherit", "snippet", "guidelines", "description"]);
+const TOOL_ENTRY_KEYS = new Set(["inherit", "snippet", "guidelines", "description", "descriptionAppend"]);
 
 function validateToolEntry(name: string, raw: unknown): ToolCatalogEntry {
 	if (!isPlainObject(raw)) {
@@ -170,9 +175,9 @@ function validateToolEntry(name: string, raw: unknown): ToolCatalogEntry {
 		return { inherit: true };
 	}
 	const hasField =
-		"snippet" in raw || "guidelines" in raw || "description" in raw;
+		"snippet" in raw || "guidelines" in raw || "description" in raw || "descriptionAppend" in raw;
 	if (!hasField) {
-		fail("tools.jsonc", `tool "${name}" needs "inherit": true or at least one of snippet/guidelines/description`);
+		fail("tools.jsonc", `tool "${name}" needs "inherit": true or at least one of snippet/guidelines/description/descriptionAppend`);
 	}
 	if ("snippet" in raw && raw.snippet !== null && typeof raw.snippet !== "string") {
 		fail("tools.jsonc", `tool "${name}".snippet must be a string or null`);
@@ -183,10 +188,13 @@ function validateToolEntry(name: string, raw: unknown): ToolCatalogEntry {
 	if ("description" in raw && typeof raw.description !== "string") {
 		fail("tools.jsonc", `tool "${name}".description must be a string`);
 	}
+	if ("descriptionAppend" in raw && typeof raw.descriptionAppend !== "string") {
+		fail("tools.jsonc", `tool "${name}".descriptionAppend must be a string`);
+	}
 	return raw as ToolCatalogEntry;
 }
 
-function validateToolCatalog(raw: unknown): ToolCatalog {
+export function validateToolCatalog(raw: unknown): ToolCatalog {
 	if (!isPlainObject(raw) || raw.version !== 1 || !isPlainObject(raw.tools)) {
 		fail("tools.jsonc", 'expected { "version": 1, "tools": { ... } }');
 	}
@@ -321,8 +329,8 @@ export function isSubagentCustomPrompt(customPrompt: unknown): boolean {
  * Apply the tool catalog to the mutable prompt options: a `snippet` string
  * replaces the tool's `<tools>` line (`null` hides it), `guidelines` replaces
  * the tool's `<rules>` lines; `{inherit:true}` entries are left untouched.
- * `description` is not applied here — it is a registration-time concern handled
- * by `extensions/prompt-guard.ts`.
+ * `description` and `descriptionAppend` are not applied here — they are
+ * registration-time concerns handled by `extensions/prompt-guard.ts`.
  *
  * Returns the selected tool names that have no catalog entry at all.
  */
diff --git a/package.json b/package.json
index f62c593..7d11065 100644
--- a/package.json
+++ b/package.json
@@ -123,6 +123,7 @@
     "extensions": [
       "./pi-overflow/capture.ts",
       "./extensions/fff-override.ts",
+      "./extensions/bash-override.ts",
       "./pi-web-search/index.ts",
       "./extensions/codegraph.ts",
       "./pi-rtk-optimizer/index.ts",
diff --git a/tests/extension-load.test.ts b/tests/extension-load.test.ts
index 5518f01..2f8de2d 100644
--- a/tests/extension-load.test.ts
+++ b/tests/extension-load.test.ts
@@ -58,6 +58,11 @@ test("all package extensions load together without global registration conflicts
 		packageJson.pi.extensions.includes("./extensions/codegraph.ts"),
 		"the bundle must expose the native codegraph_explore tool",
 	);
+	assert.equal(
+		packageJson.pi.extensions.indexOf("./extensions/bash-override.ts"),
+		packageJson.pi.extensions.indexOf("./extensions/fff-override.ts") + 1,
+		"the bash description override must register right after fff-override",
+	);
 	assert.ok(
 		packageJson.pi.extensions.includes("./pi-web-search/index.ts"),
 		"the bundle must load the unified pi-web-search tools",
@@ -292,21 +297,51 @@ test("all package extensions load together without global registration conflicts
 	const home = await mkdtemp(join(tmpdir(), "my-pi-extension-load-"));
 	const mockBin = join(home, "bin");
 	await mkdir(mockBin, { recursive: true });
-	// Probe loaded LAST: records every registered tool (name + exposure) and the
-	// final active set so the test can assert the pinned built-in codemode.
+	// Probe loaded LAST: records every registered tool (name, exposure,
+	// description, source) and the final active set so the test can assert the
+	// pinned built-in codemode. Its async setup also runs the bash override's
+	// registered definition end to end — executing `echo hi` through the same
+	// delegation path a model call would use.
 	const probeOutput = join(home, "probe-tools.json");
 	const probePath = join(home, "probe.ts");
 	await writeFile(
 		probePath,
 		[
 			'import { writeFileSync } from "node:fs";',
-			"export default function (pi: any): void {",
+			`import bashOverrideExtension from ${JSON.stringify(join(repositoryRoot, "extensions", "bash-override.ts"))};`,
+			"export default async function (pi: any): Promise<void> {",
+			"\tlet executed: unknown;",
+			"\ttry {",
+			"\t\tlet registered: any;",
+			"\t\tbashOverrideExtension({ registerTool: (tool: any) => { registered = tool; } } as any);",
+			"\t\tconst result = await registered.execute(",
+			'\t\t\t"probe-1",',
+			'\t\t\t{ command: "echo hi" },',
+			"\t\t\tundefined,",
+			"\t\t\tundefined,",
+			`\t\t\t{ cwd: ${JSON.stringify(home)}, sessionManager: { getSessionId: () => "probe-session", getSessionFile: () => undefined } } as any,`,
+			"\t\t);",
+			"\t\texecuted = {",
+			"\t\t\ttext: result?.content?.[0]?.text,",
+			"\t\t\texitCode: result?.structuredContent?.exit_code,",
+			"\t\t\thasOutputSchema: result?.structuredContent !== undefined,",
+			"\t\t\tregisteredDescription: registered?.description,",
+			"\t\t};",
+			"\t} catch (error) {",
+			"\t\texecuted = { error: String(error) };",
+			"\t}",
 			'\tpi.on("session_start", () => {',
 			"\t\twriteFileSync(",
 			`\t\t\t${JSON.stringify(probeOutput)},`,
 			"\t\t\tJSON.stringify({",
-			"\t\t\t\tall: pi.getAllTools().map((tool: any) => ({ name: tool.name, exposure: tool.exposure })),",
+			"\t\t\t\tall: pi.getAllTools().map((tool: any) => ({",
+			"\t\t\t\t\tname: tool.name,",
+			"\t\t\t\t\texposure: tool.exposure,",
+			"\t\t\t\t\tdescription: tool.description,",
+			"\t\t\t\t\tsourcePath: tool.sourceInfo?.path,",
+			"\t\t\t\t})),",
 			"\t\t\t\tactive: pi.getActiveTools(),",
+			"\t\t\t\texecuted,",
 			"\t\t\t}),",
 			"\t\t);",
 			"\t});",
@@ -337,8 +372,15 @@ test("all package extensions load together without global registration conflicts
 	assert.doesNotMatch(`${result.stdout}\n${result.stderr}`, /Failed to load extension|conflicts with/u);
 
 	const probe = JSON.parse(await readFile(probeOutput, "utf8")) as {
-		all: { name: string; exposure?: string }[];
+		all: { name: string; exposure?: string; description?: string; sourcePath?: string }[];
 		active: string[];
+		executed?: {
+			text?: string;
+			exitCode?: number;
+			hasOutputSchema?: boolean;
+			registeredDescription?: string;
+			error?: string;
+		};
 	};
 	const codemode = probe.all.find((tool) => tool.name === "codemode");
 	assert.equal(codemode?.exposure, "model-only", "Pi's built-in codemode must load with model-only exposure");
@@ -351,4 +393,31 @@ test("all package extensions load together without global registration conflicts
 		!probe.active.includes("multi_grep"),
 		"multi_grep must not appear in the active tool set",
 	);
+	const bash = probe.all.find((tool) => tool.name === "bash");
+	assert.ok(bash, "the bundle must expose the bash tool");
+	assert.ok(
+		bash.description?.startsWith("Execute a bash command in the current working directory."),
+		"the bash override must keep Pi's upstream description prefix",
+	);
+	assert.ok(
+		bash.description?.endsWith("which triggers a permission review."),
+		"the registered bash description must end with the tools.jsonc descriptionAppend",
+	);
+	assert.ok(
+		(bash.sourcePath ?? "").endsWith("extensions/bash-override.ts"),
+		`bash must be registered by extensions/bash-override.ts, got ${bash.sourcePath}`,
+	);
+	const executed = probe.executed ?? {};
+	assert.equal(executed.error, undefined, `bash override execute must not throw: ${executed.error}`);
+	assert.equal(executed.exitCode, 0, "echo hi must exit 0 through the delegated definition");
+	assert.match(executed.text ?? "", /hi/);
+	assert.equal(
+		executed.hasOutputSchema,
+		true,
+		"the bash override must keep the upstream outputSchema (structuredContent for codemode)",
+	);
+	assert.ok(
+		executed.registeredDescription?.includes("Not for searching files"),
+		"the catalog descriptionAppend must reach the registered bash description",
+	);
 });
diff --git a/tests/system-prompt.test.ts b/tests/system-prompt.test.ts
index a6474f7..4909136 100644
--- a/tests/system-prompt.test.ts
+++ b/tests/system-prompt.test.ts
@@ -21,6 +21,7 @@ import {
 	stripJsoncComments,
 	validateRoutingConfig,
 	validateSectionsConfig,
+	validateToolCatalog,
 	type MutablePromptOptions,
 	type RoutingRule,
 } from "../extensions/system-prompt-config.ts";
@@ -28,7 +29,7 @@ import systemPromptExtension, {
 	createSystemPromptComposer,
 	getSystemPromptDumpPath,
 } from "../extensions/system-prompt.ts";
-import { guardExtensionApi } from "../extensions/prompt-guard.ts";
+import { catalogDescription, guardExtensionApi } from "../extensions/prompt-guard.ts";
 import { BUNDLE_GROUP_DEFINITIONS } from "../pi-tool-search/extensions/bundle-groups.ts";
 import { BUNDLE_TOOL_SEARCH_DEFAULTS } from "../pi-tool-search/extensions/config.ts";
 
@@ -93,6 +94,20 @@ test("routing scope validation: main/subagent accepted, other values rejected",
 	);
 });
 
+test("tools.jsonc validation: descriptionAppend accepted as a string, rejected otherwise", () => {
+	assert.doesNotThrow(() =>
+		validateToolCatalog({ version: 1, tools: { bash: { descriptionAppend: "extra" } } }),
+	);
+	assert.throws(
+		() => validateToolCatalog({ version: 1, tools: { bash: { descriptionAppend: 5 } } }),
+		/descriptionAppend must be a string/,
+	);
+	assert.throws(
+		() => validateToolCatalog({ version: 1, tools: { bash: { descriptionAppend: true } } }),
+		/descriptionAppend must be a string/,
+	);
+});
+
 test("sections.jsonc validation: subagentExclude defaults to [] and rejects bad shapes", () => {
 	assert.deepEqual(validateSectionsConfig({ version: 1, order: ["tool_routing"] }), {
 		version: 1,
@@ -608,7 +623,38 @@ test("prompt guard applies catalog description overrides at registration", () =>
 	const override = loadToolCatalog().tools.edit;
 	assert.ok(override && !("inherit" in override) && typeof override.description === "string");
 	assert.equal(tools[0].description, override.description);
-	assert.equal(tools[1].description, "upstream grep", "inherit entries keep the upstream description");
+	assert.equal(tools[1].description, "upstream grep", "entries without description fields keep the upstream description");
+});
+
+test("prompt guard appends the catalog descriptionAppend to the upstream description", () => {
+	const { pi, tools } = makeRecordingPi();
+	const guarded = guardExtensionApi(pi as unknown as ExtensionAPI);
+
+	guarded.registerTool({ name: "bash", description: "upstream bash" } as never);
+	guarded.registerTool({ name: "read", description: "upstream read" } as never);
+
+	const bashEntry = loadToolCatalog().tools.bash;
+	assert.ok(bashEntry && !("inherit" in bashEntry) && typeof bashEntry.descriptionAppend === "string");
+	assert.equal(tools[0].description, `upstream bash\n\n${bashEntry.descriptionAppend}`);
+	assert.equal(tools[1].description, "upstream read", "inherit entries keep the upstream description");
+});
+
+test("catalogDescription composes override, append, and inherit", () => {
+	assert.equal(
+		catalogDescription("upstream", { description: "override", descriptionAppend: "append" }),
+		"override\n\nappend",
+		"an append sits on top of the description override when both are set",
+	);
+	assert.equal(
+		catalogDescription("upstream  \n", { descriptionAppend: "append" }),
+		"upstream\n\nappend",
+		"trailing whitespace on the base is trimmed before the blank line",
+	);
+	assert.equal(
+		catalogDescription("upstream", { inherit: true }),
+		"upstream",
+		"inherit entries are untouched",
+	);
 });
 
 test("prompt guard strips a returned systemPrompt but keeps other fields", async () => {