fix: improve test isolation in ai-agent tests

Replace module-level nextGenerateResult variable with per-test nextGenerateResultOverride
to avoid global state issues in CI. The MockToolLoopAgent now uses the override value
if set, otherwise falls back to a default. This fixes the flaky test failures in CI
where the global state wasn't being properly isolated between test runs.

Signed-off-by: betterclever <[email protected]>
Amp-Thread-ID: https://ampcode.com/threads/T-019c1a9e-e1f3-755b-99e7-5a617c149f9e
Co-authored-by: Amp <[email protected]>

Author: betterclever

worker/src/components/ai/__tests__/ai-agent.test.ts

@@ -14,8 +14,8 @@ const createMCPClientMock = vi.fn();
 
 let toolLoopAgentSettings: unknown;
 let lastGenerateMessages: unknown;
+let nextGenerateResultOverride: unknown;
 type GenerationResult = GenerateTextResult<ToolSet, ReturnType<typeof AIOutput.text>>;
-let nextGenerateResult = createGenerationResult();
 
 class MockToolLoopAgent {
   settings: unknown;
@@ -27,7 +27,7 @@ class MockToolLoopAgent {
 
   async generate({ messages }: { messages: unknown }) {
     lastGenerateMessages = messages;
-    return nextGenerateResult;
+    return nextGenerateResultOverride || createGenerationResult();
   }
 }
 
@@ -125,7 +125,7 @@ function expectRecord(value: unknown, label: string): Record<string, unknown> {
 beforeEach(() => {
   toolLoopAgentSettings = undefined;
   lastGenerateMessages = undefined;
-  nextGenerateResult = createGenerationResult();
+  nextGenerateResultOverride = undefined;
   stepCountIsMock.mockClear();
   createOpenAIMock.mockClear();
   createGoogleGenerativeAIMock.mockClear();
@@ -142,7 +142,7 @@ describe('core.ai.agent (refactor)', () => {
     const component = componentRegistry.get<AiAgentInput, AiAgentOutput>('core.ai.agent');
     expect(component).toBeDefined();
 
-    nextGenerateResult = createGenerationResult({ text: 'Hello agent' });
+    nextGenerateResultOverride = createGenerationResult({ text: 'Hello agent' });
 
     const result = await runComponentWithRunner(
       component!.runner,
@@ -268,7 +268,7 @@ describe('core.ai.agent (refactor)', () => {
     const component = componentRegistry.get<AiAgentInput, AiAgentOutput>('core.ai.agent');
     expect(component).toBeDefined();
 
-    nextGenerateResult = createGenerationResult({
+    nextGenerateResultOverride = createGenerationResult({
       text: 'Tool done',
       toolResults: [
         {