fix: remove failed user content from history to prevent cascading 400 errors

packages/core/src/core/geminiChat.test.ts

@@ -169,7 +169,7 @@
       modelConfigService: {
         getResolvedConfig: vi.fn().mockImplementation((modelConfigKey) => {
           const model = modelConfigKey.model ?? mockConfig.getModel();
           const thinkingConfig = model.startsWith('gemini-3')
             ? {
                 thinkingLevel: ThinkingLevel.HIGH,
               }
@@ -918,7 +918,7 @@
       );
     });
 
     it('should use thinkingLevel and remove thinkingBudget for gemini-3 models', async () => {
       const response = (async function* () {
         yield {
           candidates: [
@@ -934,7 +934,7 @@
       );
 
       const stream = await chat.sendMessageStream(
         { model: 'gemini-3-test-only-model-string-for-testing' },
         'hello',
         'prompt-id-thinking-level',
         new AbortController().signal,
@@ -945,7 +945,7 @@
 
       expect(mockContentGenerator.generateContentStream).toHaveBeenCalledWith(
         expect.objectContaining({
           model: 'gemini-3-test-only-model-string-for-testing',
           config: expect.objectContaining({
             thinkingConfig: {
               thinkingBudget: undefined,
@@ -957,7 +957,7 @@
       );
     });
 
     it('should use thinkingBudget and remove thinkingLevel for non-gemini-3 models', async () => {
       const response = (async function* () {
         yield {
           candidates: [
@@ -1028,7 +1028,7 @@
   });
 
   describe('sendMessageStream with retries', () => {
     it('should not retry on invalid content if model does not start with gemini-2', async () => {
       // Mock the stream to fail.
       vi.mocked(mockContentGenerator.generateContentStream).mockImplementation(
         async () =>
@@ -1279,13 +1279,10 @@
       expect(mockLogContentRetry).toHaveBeenCalledTimes(1);
       expect(mockLogContentRetryFailure).toHaveBeenCalledTimes(1);
 
-      // History should still contain the user message.
+      // History should NOT contain the failed user message,
+      // to prevent invalid content from breaking subsequent requests.
       const history = chat.getHistory();
-      expect(history.length).toBe(1);
-      expect(history[0]).toEqual({
-        role: 'user',
-        parts: [{ text: 'test' }],
-      });
+      expect(history.length).toBe(0);
     });
 
     describe('API error retry behavior', () => {

packages/core/src/core/geminiChat.ts

@@ -380,6 +380,8 @@ export class GeminiChat {
             }
 
             if (isConnectionPhase) {
+              // Remove failed user content so it doesn't break subsequent requests
+              this.history.pop();
               throw error;
             }
             lastError = error;
@@ -429,6 +431,8 @@ export class GeminiChat {
               new ContentRetryFailureEvent(maxAttempts, lastError.type, model),
             );
           }
+          // Remove failed user content so it doesn't break subsequent requests
+          this.history.pop();
           throw lastError;
         }
       } finally {