fix(bash-bg): stop overriding the built-in bash tool

.changeset/bash-bg-fix-resume-cwd.md

@@ -0,0 +1,5 @@
+---
+"pi-bash-bg": patch
+---
+
+Stop overriding the built-in bash tool so resumed sessions run bash in the session's cwd.

AGENTS.md

@@ -33,7 +33,7 @@ yarn lint           # biome check
 yarn lint:fix       # biome check --write
 ```
 
-After completing changes, include a changeset file for affected packages (`yarn changeset`). See `DEVELOPMENT.md` for the release workflow.
+After completing changes, include a changeset file for affected packages (`yarn changeset`). Keep changeset summaries to a single line whenever possible; users see them rendered in the CHANGELOG, so be concise. See `DEVELOPMENT.md` for the release workflow.
 
 ## Gotchas
 

packages/bash-bg/README.md

@@ -8,7 +8,7 @@ The bash tool pipes stdout/stderr from the spawned shell. When a command backgro
 
 ## Solution
 
-This extension intercepts bash tool calls, parses the command with [@aliou/sh](https://github.com/nicolo-ribaudo/sh) to detect background processes (`stmt.background === true`), appends background-job guidance to the bash tool description, and rewrites the command to:
+This extension intercepts bash tool calls, parses the command with [@aliou/sh](https://github.com/nicolo-ribaudo/sh) to detect background processes (`stmt.background === true`), and rewrites the command to:
 
 1. **Redirect output** to temp log files with human-readable names based on the command label, so background processes release the pipes
 2. **Add `disown`** to detach from job control (if not already present)
@@ -78,10 +78,6 @@ echo "[bg] pid=$! label=npm start log=/tmp/pi-bg-npm-start-3.log"
 
 If the command already has `disown` after the `&`, no duplicate is added.
 
-### Bash tool description
-
-The extension appends a short background-job summary to the bash tool description, so the model sees it directly in tool metadata.
-
 ## Supported patterns
 
 | Pattern | Handled |

packages/bash-bg/src/index.ts

@@ -15,23 +15,14 @@
  */
 
 import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
-import { createBashTool, isToolCallEventType } from "@mariozechner/pi-coding-agent";
+import { isToolCallEventType } from "@mariozechner/pi-coding-agent";
 import { detectBackground } from "./detect.js";
 import { rewriteCommand } from "./rewrite.js";
 
 export { detectBackground, type BgStatement, type DetectResult } from "./detect.js";
 export { rewriteCommand, findBgOperatorPositions, type BgProcessInfo, type RewriteResult } from "./rewrite.js";
 
-const BASH_DESCRIPTION_APPENDIX =
-	"Background jobs continue running after the command returns. Their output is captured to a log file even without explicit redirection. The PID and log path will be returned.";
-
 export default function (pi: ExtensionAPI) {
-	const bashTool = createBashTool(process.cwd());
-	pi.registerTool({
-		...bashTool,
-		description: `${bashTool.description} ${BASH_DESCRIPTION_APPENDIX}`,
-	});
-
 	pi.on("tool_call", async (event) => {
 		if (!isToolCallEventType("bash", event)) return;
 

packages/bash-bg/test/index.test.ts

@@ -1,25 +1,86 @@
-import type { ExtensionAPI, ToolDefinition } from "@mariozechner/pi-coding-agent";
+import type { ExtensionAPI, ToolCallEvent, ToolCallEventResult, ToolDefinition } from "@mariozechner/pi-coding-agent";
 import { describe, expect, it, vi } from "vitest";
 import extension from "../src/index.js";
 
+type ToolCallHandler = (
+	event: ToolCallEvent,
+	ctx: unknown,
+) => Promise<ToolCallEventResult | undefined> | ToolCallEventResult | undefined;
+
+function loadExtension() {
+	const tools: ToolDefinition[] = [];
+	let toolCallHandler: ToolCallHandler | undefined;
+	const pi = {
+		registerTool: vi.fn((tool: ToolDefinition) => {
+			tools.push(tool);
+		}),
+		on: vi.fn((event: string, handler: ToolCallHandler) => {
+			if (event === "tool_call") toolCallHandler = handler;
+		}),
+	} as unknown as ExtensionAPI;
+
+	extension(pi);
+
+	return { pi, tools, toolCallHandler };
+}
+
 describe("pi-bash-bg extension", () => {
-	it("appends background job guidance to the bash tool description", () => {
-		const tools: ToolDefinition[] = [];
-		const pi = {
-			registerTool(tool) {
-				tools.push(tool);
-			},
-			on: vi.fn(),
-		} as unknown as ExtensionAPI;
-
-		extension(pi);
-
-		const bashTool = tools.find((tool) => tool.name === "bash");
-		expect(bashTool).toBeDefined();
-		expect(bashTool?.description).toContain("Background jobs continue running after the command returns.");
-		expect(bashTool?.description).toContain(
-			"Their output is captured to a log file even without explicit redirection.",
-		);
-		expect(bashTool?.description).toContain("The PID and log path will be returned.");
+	it("does not override the built-in bash tool", () => {
+		// Replacing the built-in bash tool would force a fixed cwd captured at
+		// extension load time, which breaks the cwd of resumed sessions.
+		const { pi, tools } = loadExtension();
+		expect(tools).toHaveLength(0);
+		expect(pi.registerTool).not.toHaveBeenCalled();
+	});
+
+	it("registers a tool_call handler", () => {
+		const { pi, toolCallHandler } = loadExtension();
+		expect(pi.on).toHaveBeenCalledWith("tool_call", expect.any(Function));
+		expect(toolCallHandler).toBeDefined();
+	});
+
+	it("rewrites bash commands that contain background statements", async () => {
+		const { toolCallHandler } = loadExtension();
+		const event: ToolCallEvent = {
+			type: "tool_call",
+			toolName: "bash",
+			toolCallId: "id",
+			input: { command: "sleep 300 &" },
+		};
+
+		await toolCallHandler!(event, {});
+
+		const rewritten = (event.input as { command: string }).command;
+		expect(rewritten).not.toBe("sleep 300 &");
+		expect(rewritten).toContain("disown");
+		expect(rewritten).toContain("[bg]");
+	});
+
+	it("leaves non-background bash commands untouched", async () => {
+		const { toolCallHandler } = loadExtension();
+		const event: ToolCallEvent = {
+			type: "tool_call",
+			toolName: "bash",
+			toolCallId: "id",
+			input: { command: "echo hi && ls" },
+		};
+
+		await toolCallHandler!(event, {});
+
+		expect((event.input as { command: string }).command).toBe("echo hi && ls");
+	});
+
+	it("ignores non-bash tool calls", async () => {
+		const { toolCallHandler } = loadExtension();
+		const event: ToolCallEvent = {
+			type: "tool_call",
+			toolName: "read",
+			toolCallId: "id",
+			input: { path: "foo &" },
+		};
+
+		await toolCallHandler!(event, {});
+
+		expect((event.input as { path: string }).path).toBe("foo &");
 	});
 });