fix(coding-agent): restore builtin-only tool disabling

closes #3592

packages/coding-agent/test/args.test.ts

@@ -257,17 +257,48 @@ describe("parseArgs", () => {
 		});
 	});
 
-	describe("--no-tools flag", () => {
+	describe("tool flags", () => {
 		test("parses --no-tools flag", () => {
 			const result = parseArgs(["--no-tools"]);
 			expect(result.noTools).toBe(true);
 		});
 
+		test("parses -nt shorthand", () => {
+			const result = parseArgs(["-nt"]);
+			expect(result.noTools).toBe(true);
+		});
+
+		test("parses --no-builtin-tools flag", () => {
+			const result = parseArgs(["--no-builtin-tools"]);
+			expect(result.noBuiltinTools).toBe(true);
+		});
+
+		test("parses -nbt shorthand", () => {
+			const result = parseArgs(["-nbt"]);
+			expect(result.noBuiltinTools).toBe(true);
+		});
+
+		test("parses --tools flag", () => {
+			const result = parseArgs(["--tools", "read,bash"]);
+			expect(result.tools).toEqual(["read", "bash"]);
+		});
+
+		test("parses -t shorthand", () => {
+			const result = parseArgs(["-t", "read,bash"]);
+			expect(result.tools).toEqual(["read", "bash"]);
+		});
+
 		test("parses --no-tools with explicit --tools flags", () => {
 			const result = parseArgs(["--no-tools", "--tools", "read,bash"]);
 			expect(result.noTools).toBe(true);
 			expect(result.tools).toEqual(["read", "bash"]);
 		});
+
+		test("parses --no-builtin-tools with explicit --tools flags", () => {
+			const result = parseArgs(["--no-builtin-tools", "--tools", "read,bash"]);
+			expect(result.noBuiltinTools).toBe(true);
+			expect(result.tools).toEqual(["read", "bash"]);
+		});
 	});
 
 	describe("messages and file args", () => {

packages/coding-agent/test/suite/regressions/3592-no-builtin-tools-keeps-extension-tools.test.ts

@@ -0,0 +1,93 @@
+import { existsSync, mkdirSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { getModel } from "@mariozechner/pi-ai";
+import { Type } from "typebox";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { DefaultResourceLoader } from "../../../src/core/resource-loader.js";
+import { createAgentSession } from "../../../src/core/sdk.js";
+import { SessionManager } from "../../../src/core/session-manager.js";
+import { SettingsManager } from "../../../src/core/settings-manager.js";
+
+describe("regression #3592: no-builtin-tools keeps extension tools enabled", () => {
+	let tempDir: string;
+	let agentDir: string;
+
+	beforeEach(() => {
+		tempDir = join(tmpdir(), `pi-no-builtin-tools-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+		agentDir = join(tempDir, "agent");
+		mkdirSync(agentDir, { recursive: true });
+	});
+
+	afterEach(() => {
+		if (tempDir && existsSync(tempDir)) {
+			rmSync(tempDir, { recursive: true, force: true });
+		}
+	});
+
+	async function createSession(options?: { noTools?: "all" | "builtin"; tools?: string[] }) {
+		const settingsManager = SettingsManager.create(tempDir, agentDir);
+		const sessionManager = SessionManager.inMemory(tempDir);
+		const resourceLoader = new DefaultResourceLoader({
+			cwd: tempDir,
+			agentDir,
+			settingsManager,
+			extensionFactories: [
+				(pi) => {
+					pi.on("session_start", () => {
+						pi.registerTool({
+							name: "dynamic_tool",
+							label: "Dynamic Tool",
+							description: "Tool registered from session_start",
+							promptSnippet: "Run dynamic test behavior",
+							parameters: Type.Object({}),
+							execute: async () => ({
+								content: [{ type: "text", text: "ok" }],
+								details: {},
+							}),
+						});
+					});
+				},
+			],
+		});
+		await resourceLoader.reload();
+
+		const { session } = await createAgentSession({
+			cwd: tempDir,
+			agentDir,
+			model: getModel("anthropic", "claude-sonnet-4-5")!,
+			settingsManager,
+			sessionManager,
+			resourceLoader,
+			noTools: options?.noTools,
+			tools: options?.tools,
+		});
+		await session.bindExtensions({});
+		return session;
+	}
+
+	it("keeps extension tools active when built-in defaults are disabled", async () => {
+		const session = await createSession({ noTools: "builtin" });
+
+		expect(
+			session
+				.getAllTools()
+				.map((tool) => tool.name)
+				.sort(),
+		).toEqual(["bash", "dynamic_tool", "edit", "find", "grep", "ls", "read", "write"]);
+		expect(session.getActiveToolNames()).toEqual(["dynamic_tool"]);
+		expect(session.systemPrompt).toContain("- dynamic_tool: Run dynamic test behavior");
+		expect(session.systemPrompt).not.toContain("- read:");
+		expect(session.systemPrompt).not.toContain("- bash:");
+		session.dispose();
+	});
+
+	it("still disables all tools when noTools is all", async () => {
+		const session = await createSession({ noTools: "all" });
+
+		expect(session.getAllTools()).toEqual([]);
+		expect(session.getActiveToolNames()).toEqual([]);
+		expect(session.systemPrompt).toContain("Available tools:\n(none)");
+		session.dispose();
+	});
+});