test(toolsets): add runtime validation test for mutually exclusive accounts

Add test to verify ToolSetConfigError is thrown when both accountId and
accountIds are provided at runtime. Uses 'as never' to bypass TypeScript
type checking and simulate JavaScript usage scenarios.

Author: ryoppippi

src/toolsets.test.ts

@@ -130,6 +130,24 @@ describe('StackOneToolSet', () => {
 			expect(toolsetMultiple.accountIds).toEqual(['account-1', 'account-2']);
 		});
 
+		it('should throw error when both accountId and accountIds are provided at runtime', () => {
+			// Runtime validation for JavaScript users or when TypeScript is bypassed
+			expect(() => {
+				new StackOneToolSet({
+					apiKey: 'custom_key',
+					accountId: 'primary-account',
+					accountIds: ['account-1', 'account-2'],
+				} as never); // Use 'as never' to bypass TypeScript for runtime test
+			}).toThrow(ToolSetConfigError);
+			expect(() => {
+				new StackOneToolSet({
+					apiKey: 'custom_key',
+					accountId: 'primary-account',
+					accountIds: ['account-1', 'account-2'],
+				} as never);
+			}).toThrow(/Cannot provide both accountId and accountIds/);
+		});
+
 		it('should set baseUrl from config', () => {
 			const toolset = new StackOneToolSet({
 				apiKey: 'custom_key',