feat(coding-agent): enable tools newly added to defaultTools on reload

When the session's initial tools come from defaultTools, /reload activates
names added to the resolved selection. Removals do not deactivate tools, and
explicit --tools/--no-tools/--no-builtin-tools keep overriding the setting.

closes #10245

packages/coding-agent/CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Added a `description` field for MCP servers (`pi mcp add --description`), shown with the server in the system prompt and used to rank its tools in tool search, and a `describeNamespace(name)` codemode helper that returns a namespace's instructions and tool names. `describeNamespace()` and `searchTools()` accept a namespace as `mcp__dev-radius`, `mcp__dev_radius`, `dev-radius`, or `dev_radius`.
 - Added an `oauth.clientName` setting for MCP servers (`pi mcp add --oauth-client-name`) to change the client name sent during OAuth client registration, for servers such as Figma that only accept known clients ([#10226](https://github.com/earendil-works/pi/issues/10226)).
+- `/reload` now enables tools newly added to the `defaultTools` setting. Tools removed from it stay enabled, tools turned off during the session stay off unless newly added, and `--tools`, `--no-tools`, and `--no-builtin-tools` still override the setting ([#10245](https://github.com/earendil-works/pi/issues/10245)).
 
 ### Changed
 

packages/coding-agent/docs/settings.md

@@ -53,6 +53,8 @@ A list of only `+name` and `-name` entries changes the inherited selection inste
 
 This replaces `bash` with `powershell` and enables `grep`: `["-bash", "+powershell", "+grep"]`. Project settings apply on top of user settings: a project list with only `+name` and `-name` entries changes the user's selection, and a project list with a plain name replaces it. In one list, plain names form the selection, and `+name` and `-name` then apply in order.
 
+`/reload` enables tools newly added to `defaultTools`. It does not disable tools removed from it or re-enable unchanged tools you turned off. `--tools`, `--no-tools`, and `--no-builtin-tools` override `defaultTools`, also on reload.
+
 CLI tool options override this setting for one invocation; `--tools` does not accept `+name` or `-name`. See [Command Line](cli.md#tools).
 
 ## Sessions and context

packages/coding-agent/src/core/agent-session.ts

@@ -129,7 +129,7 @@ import {
 	SessionManager,
 	type SessionProjection,
 } from "./session-manager.ts";
-import type { CacheWarmingMode, SettingsManager } from "./settings-manager.ts";
+import { type CacheWarmingMode, DEFAULT_TOOL_NAMES, type SettingsManager } from "./settings-manager.ts";
 import type { SlashCommandInfo } from "./slash-commands.ts";
 import { BUILTIN_PATH_PREFIX, createSyntheticSourceInfo, isSyntheticPath, type SourceInfo } from "./source-info.ts";
 import {
@@ -260,6 +260,11 @@ export interface AgentSessionConfig {
 	cacheWarmer?: Pick<CacheWarmer, "cancel" | "status" | "onAgentSettled" | "onModeChanged" | "onWarmed">;
 	/** Initial active built-in tool names. Default: [read, bash, edit, write] */
 	initialActiveToolNames?: string[];
+	/**
+	 * Whether the initial tools come from the `defaultTools` setting. When true, reload activates
+	 * tools newly added to the setting. Tools removed from it stay active.
+	 */
+	usesDefaultTools?: boolean;
 	/** Optional allowlist of tool names. When provided, only these tool names are exposed. */
 	allowedToolNames?: string[];
 	/** Optional denylist of tool names. When provided, these tool names are not exposed. */
@@ -418,6 +423,7 @@ export class AgentSession {
 	private _cwd: string;
 	private _extensionRunnerRef?: { current?: ExtensionRunner };
 	private _initialActiveToolNames?: string[];
+	private _usesDefaultTools: boolean;
 	private _allowedToolNames?: Set<string>;
 	private _excludedToolNames?: Set<string>;
 	private _baseToolsOverride?: Record<string, AgentTool>;
@@ -462,6 +468,7 @@ export class AgentSession {
 		}
 		this._extensionRunnerRef = config.extensionRunnerRef;
 		this._initialActiveToolNames = config.initialActiveToolNames;
+		this._usesDefaultTools = config.usesDefaultTools ?? false;
 		this._allowedToolNames = config.allowedToolNames ? new Set(config.allowedToolNames) : undefined;
 		this._excludedToolNames = config.excludedToolNames ? new Set(config.excludedToolNames) : undefined;
 		this._baseToolsOverride = config.baseToolsOverride;
@@ -3582,12 +3589,22 @@ export class AgentSession {
 		const previousFlagValues = oldRunner.getFlagValues();
 		await emitSessionShutdownEvent(oldRunner, { type: "session_shutdown", reason: "reload" });
 		oldRunner.invalidate();
+		const previousDefaultTools = new Set(
+			this._usesDefaultTools ? (this.settingsManager.getDefaultTools() ?? DEFAULT_TOOL_NAMES) : [],
+		);
 		await this.settingsManager.reload();
 		this.syncQueueModesFromSettings();
 		resetApiProviders();
 		await this._resourceLoader.reload();
+		// Activate tools newly added to defaultTools. Removed ones stay active, and tools disabled
+		// during the session stay disabled unless the setting newly adds them.
+		const addedDefaultTools = this._usesDefaultTools
+			? (this.settingsManager.getDefaultTools() ?? DEFAULT_TOOL_NAMES).filter(
+					(name) => !previousDefaultTools.has(name),
+				)
+			: [];
 		this._buildRuntime({
-			activeToolNames: this.getActiveToolNames(),
+			activeToolNames: [...this.getActiveToolNames(), ...addedDefaultTools],
 			flagValues: previousFlagValues,
 			includeAllExtensionTools: true,
 		});

packages/coding-agent/src/core/sdk.ts

@@ -445,6 +445,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 		modelRuntime,
 		cacheWarmer,
 		initialActiveToolNames,
+		usesDefaultTools: options.tools === undefined && !options.noTools,
 		allowedToolNames,
 		excludedToolNames,
 		extensionRunnerRef,

packages/coding-agent/test/default-tools-setting.test.ts

@@ -1,4 +1,4 @@
-import { existsSync, mkdirSync, rmSync } from "node:fs";
+import { existsSync, mkdirSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { getModel } from "@earendil-works/pi-ai/compat";
@@ -156,6 +156,84 @@ describe("defaultTools setting", () => {
 		toolLessSession.dispose();
 	});
 
+	describe("reload", () => {
+		const inactiveTool: InlineExtension = (pi) => {
+			pi.registerTool({
+				name: "inactive_tool",
+				label: "Inactive Tool",
+				description: "Extension tool registered inactive",
+				parameters: Type.Object({}),
+				execute: async () => ({ content: [{ type: "text", text: "ok" }], details: {} }),
+				defaultActive: false,
+			});
+		};
+
+		const writeSettings = (settings: object) =>
+			writeFileSync(join(agentDir, "settings.json"), JSON.stringify(settings));
+
+		async function createFileSession(options: ToolOptions = {}) {
+			const settingsManager = SettingsManager.create(tempDir, agentDir);
+			const resourceLoader = new DefaultResourceLoader({
+				cwd: tempDir,
+				agentDir,
+				settingsManager,
+				extensionFactories: [inactiveTool],
+			});
+			await resourceLoader.reload();
+			return (
+				await createAgentSession({
+					cwd: tempDir,
+					agentDir,
+					model: getModel("anthropic", "claude-sonnet-4-5")!,
+					settingsManager,
+					sessionManager: SessionManager.inMemory(tempDir),
+					resourceLoader,
+					...options,
+				})
+			).session;
+		}
+
+		// #10245
+		it("activates only tools newly added to defaultTools", async () => {
+			const session = await createFileSession();
+			expect(session.getActiveToolNames()).toEqual(["read", "bash", "edit", "write"]);
+			session.setActiveToolsByName(["read", "edit", "write"]);
+
+			writeSettings({ defaultTools: ["+inactive_tool", "+grep"] });
+			await session.reload();
+			// bash was disabled during the session and is not newly added, so it stays off.
+			expect(session.getActiveToolNames().sort()).toEqual(["edit", "grep", "inactive_tool", "read", "write"]);
+
+			// Removing tools from the setting does not disable them.
+			writeSettings({ defaultTools: ["-read"] });
+			await session.reload();
+			expect(session.getActiveToolNames().sort()).toEqual(["edit", "grep", "inactive_tool", "read", "write"]);
+			session.dispose();
+		});
+
+		it("keeps explicit tool options on reload", async () => {
+			const allowlisted = await createFileSession({ tools: ["read"] });
+			writeSettings({ defaultTools: ["+grep"] });
+			await allowlisted.reload();
+			expect(allowlisted.getActiveToolNames()).toEqual(["read"]);
+			allowlisted.dispose();
+
+			writeSettings({});
+			const builtinless = await createFileSession({ noTools: "builtin" });
+			writeSettings({ defaultTools: ["+grep"] });
+			await builtinless.reload();
+			expect(builtinless.getActiveToolNames()).toEqual([]);
+			builtinless.dispose();
+
+			writeSettings({});
+			const excluded = await createFileSession({ excludeTools: ["grep"] });
+			writeSettings({ defaultTools: ["+grep", "+inactive_tool"] });
+			await excluded.reload();
+			expect(excluded.getActiveToolNames().sort()).toEqual(["bash", "edit", "inactive_tool", "read", "write"]);
+			excluded.dispose();
+		});
+	});
+
 	it("applies through service-based session creation", async () => {
 		const settingsManager = SettingsManager.inMemory({ defaultTools: ["ls"] });
 		const services = await createAgentSessionServices({ cwd: tempDir, agentDir, settingsManager });