test(toolsets): add type-level tests for StackOneToolSetConfig

Add comprehensive type tests using vitest's expectTypeOf to verify
the MergeExclusive behaviour of account configuration options:

- Test that accountId alone is valid
- Test that accountIds alone is valid
- Test that neither is valid (optional)
- Test that both together is rejected by the type system
- Verify accountId is typed as string | undefined
- Verify accountIds is typed as string[] | undefined

Author: ryoppippi

src/toolsets.test-d.ts

@@ -0,0 +1,44 @@
+import { expectTypeOf } from 'vitest';
+import type { StackOneToolSetConfig } from './toolsets';
+
+// Valid configurations - only accountId
+test('StackOneToolSetConfig accepts only accountId', () => {
+	expectTypeOf<{
+		apiKey: string;
+		accountId: string;
+	}>().toMatchTypeOf<StackOneToolSetConfig>();
+});
+
+// Valid configurations - only accountIds
+test('StackOneToolSetConfig accepts only accountIds', () => {
+	expectTypeOf<{
+		apiKey: string;
+		accountIds: string[];
+	}>().toMatchTypeOf<StackOneToolSetConfig>();
+});
+
+// Valid configurations - neither accountId nor accountIds
+test('StackOneToolSetConfig accepts neither accountId nor accountIds', () => {
+	expectTypeOf<{
+		apiKey: string;
+	}>().toMatchTypeOf<StackOneToolSetConfig>();
+});
+
+// Invalid configuration - both accountId and accountIds should NOT match
+test('StackOneToolSetConfig rejects both accountId and accountIds', () => {
+	expectTypeOf<{
+		apiKey: string;
+		accountId: string;
+		accountIds: string[];
+	}>().not.toMatchTypeOf<StackOneToolSetConfig>();
+});
+
+// Verify accountId can be string or undefined
+test('accountId is typed as string | undefined', () => {
+	expectTypeOf<StackOneToolSetConfig['accountId']>().toEqualTypeOf<string | undefined>();
+});
+
+// Verify accountIds can be string[] or undefined
+test('accountIds is typed as string[] | undefined', () => {
+	expectTypeOf<StackOneToolSetConfig['accountIds']>().toEqualTypeOf<string[] | undefined>();
+});