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

closes #3592

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

@@ -47,11 +47,19 @@ export interface CreateAgentSessionOptions {
 	/** Models available for cycling (Ctrl+P in interactive mode) */
 	scopedModels?: Array<{ model: Model<any>; thinkingLevel?: ThinkingLevel }>;
 
+	/**
+	 * Optional default tool suppression mode when no explicit allowlist is provided.
+	 *
+	 * - "all": start with no tools enabled
+	 * - "builtin": disable the default built-in tools (read, bash, edit, write)
+	 *   but keep extension/custom tools enabled
+	 */
+	noTools?: "all" | "builtin";
 	/**
 	 * Optional allowlist of tool names.
 	 *
 	 * When omitted, pi enables the default built-in tools (read, bash, edit, write)
-	 * and leaves extension/custom tools enabled.
+	 * and leaves extension/custom tools enabled unless `noTools` changes that default.
 	 * When provided, only the listed tool names are enabled.
 	 */
 	tools?: string[];
@@ -245,7 +253,12 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 	}
 
 	const defaultActiveToolNames: ToolName[] = ["read", "bash", "edit", "write"];
-	const initialActiveToolNames: string[] = options.tools ? [...options.tools] : defaultActiveToolNames;
+	const allowedToolNames = options.tools ?? (options.noTools === "all" ? [] : undefined);
+	const initialActiveToolNames: string[] = options.tools
+		? [...options.tools]
+		: options.noTools
+			? []
+			: defaultActiveToolNames;
 
 	let agent: Agent;
 
@@ -366,7 +379,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 		customTools: options.customTools,
 		modelRegistry,
 		initialActiveToolNames,
-		allowedToolNames: options.tools,
+		allowedToolNames,
 		extensionRunnerRef,
 		sessionStartEvent: options.sessionStartEvent,
 	});