Ensure a Strictly Alternating Message History (#6995)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

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

@@ -76,6 +76,142 @@ describe('GeminiChat', () => {
   });
 
   describe('sendMessage', () => {
+    it('should throw an error when attempting to add a user turn after another user turn', async () => {
+      // 1. Setup: Create a history that already ends with a user turn (a functionResponse).
+      const initialHistory: Content[] = [
+        { role: 'user', parts: [{ text: 'Initial prompt' }] },
+        {
+          role: 'model',
+          parts: [{ functionCall: { name: 'test_tool', args: {} } }],
+        },
+        {
+          role: 'user',
+          parts: [{ functionResponse: { name: 'test_tool', response: {} } }],
+        },
+      ];
+      chat.setHistory(initialHistory);
+
+      // 2. Mock a valid model response so the call doesn't fail for other reasons.
+      const mockResponse = {
+        candidates: [
+          { content: { role: 'model', parts: [{ text: 'some response' }] } },
+        ],
+      } as unknown as GenerateContentResponse;
+      vi.mocked(mockModelsModule.generateContent).mockResolvedValue(
+        mockResponse,
+      );
+
+      // 3. Action & Assert: Expect that sending another user message immediately
+      //    after a user-role turn throws the specific error.
+      await expect(
+        chat.sendMessage(
+          { message: 'This is an invalid consecutive user message' },
+          'prompt-id-1',
+        ),
+      ).rejects.toThrow('Cannot add a user turn after another user turn.');
+    });
+    it('should preserve text parts that are in the same response as a thought', async () => {
+      // 1. Mock the API to return a single response containing both a thought and visible text.
+      const mixedContentResponse = {
+        candidates: [
+          {
+            content: {
+              role: 'model',
+              parts: [
+                { thought: 'This is a thought.' },
+                { text: 'This is the visible text that should not be lost.' },
+              ],
+            },
+          },
+        ],
+      } as unknown as GenerateContentResponse;
+
+      vi.mocked(mockModelsModule.generateContent).mockResolvedValue(
+        mixedContentResponse,
+      );
+
+      // 2. Action: Send a standard, non-streaming message.
+      await chat.sendMessage(
+        { message: 'test message' },
+        'prompt-id-mixed-response',
+      );
+
+      // 3. Assert: Check the final state of the history.
+      const history = chat.getHistory();
+
+      // The history should contain two turns: the user's message and the model's response.
+      expect(history.length).toBe(2);
+
+      const modelTurn = history[1]!;
+      expect(modelTurn.role).toBe('model');
+
+      // CRUCIAL ASSERTION:
+      // Buggy code would discard the entire response because a "thought" was present,
+      // resulting in an empty placeholder turn with 0 parts.
+      // The corrected code will pass, preserving the single visible text part.
+      expect(modelTurn?.parts?.length).toBe(1);
+      expect(modelTurn?.parts![0]!.text).toBe(
+        'This is the visible text that should not be lost.',
+      );
+    });
+    it('should add a placeholder model turn when a tool call is followed by an empty model response', async () => {
+      // 1. Setup: A history where the model has just made a function call.
+      const initialHistory: Content[] = [
+        {
+          role: 'user',
+          parts: [{ text: 'Find a good Italian restaurant for me.' }],
+        },
+        {
+          role: 'model',
+          parts: [
+            {
+              functionCall: {
+                name: 'find_restaurant',
+                args: { cuisine: 'Italian' },
+              },
+            },
+          ],
+        },
+      ];
+      chat.setHistory(initialHistory);
+
+      // 2. Mock the API to return an empty/thought-only response.
+      const emptyModelResponse = {
+        candidates: [
+          { content: { role: 'model', parts: [{ thought: true }] } },
+        ],
+      } as unknown as GenerateContentResponse;
+      vi.mocked(mockModelsModule.generateContent).mockResolvedValue(
+        emptyModelResponse,
+      );
+
+      // 3. Action: Send the function response back to the model.
+      await chat.sendMessage(
+        {
+          message: {
+            functionResponse: {
+              name: 'find_restaurant',
+              response: { name: 'Vesuvio' },
+            },
+          },
+        },
+        'prompt-id-1',
+      );
+
+      // 4. Assert: The history should now have four valid, alternating turns.
+      const history = chat.getHistory();
+      expect(history.length).toBe(4);
+
+      // The final turn must be the empty model placeholder.
+      const lastTurn = history[3]!;
+      expect(lastTurn.role).toBe('model');
+      expect(lastTurn?.parts?.length).toBe(0);
+
+      // The second-to-last turn must be the function response we sent.
+      const secondToLastTurn = history[2]!;
+      expect(secondToLastTurn.role).toBe('user');
+      expect(secondToLastTurn?.parts![0]!.functionResponse).toBeDefined();
+    });
     it('should call generateContent with the correct parameters', async () => {
       const response = {
         candidates: [
@@ -107,6 +243,282 @@ describe('GeminiChat', () => {
   });
 
   describe('sendMessageStream', () => {
+    it('should not consolidate text into a part that also contains a functionCall', async () => {
+      // 1. Mock the API to stream a malformed part followed by a valid text part.
+      const multiChunkStream = (async function* () {
+        // This malformed part has both text and a functionCall.
+        yield {
+          candidates: [
+            {
+              content: {
+                role: 'model',
+                parts: [
+                  {
+                    text: 'Some text',
+                    functionCall: { name: 'do_stuff', args: {} },
+                  },
+                ],
+              },
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+        // This valid text part should NOT be merged into the malformed one.
+        yield {
+          candidates: [
+            {
+              content: {
+                role: 'model',
+                parts: [{ text: ' that should not be merged.' }],
+              },
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+
+      vi.mocked(mockModelsModule.generateContentStream).mockResolvedValue(
+        multiChunkStream,
+      );
+
+      // 2. Action: Send a message and consume the stream.
+      const stream = await chat.sendMessageStream(
+        { message: 'test message' },
+        'prompt-id-malformed-chunk',
+      );
+      for await (const _ of stream) {
+        // Consume the stream to trigger history recording.
+      }
+
+      // 3. Assert: Check that the final history was not incorrectly consolidated.
+      const history = chat.getHistory();
+
+      expect(history.length).toBe(2);
+      const modelTurn = history[1]!;
+
+      // CRUCIAL ASSERTION: There should be two separate parts.
+      // The old, non-strict logic would incorrectly merge them, resulting in one part.
+      expect(modelTurn?.parts?.length).toBe(2);
+
+      // Verify the contents of each part.
+      expect(modelTurn?.parts![0]!.text).toBe('Some text');
+      expect(modelTurn?.parts![0]!.functionCall).toBeDefined();
+      expect(modelTurn?.parts![1]!.text).toBe(' that should not be merged.');
+    });
+
+    it('should consolidate subsequent text chunks after receiving an empty text chunk', async () => {
+      // 1. Mock the API to return a stream where one chunk is just an empty text part.
+      const multiChunkStream = (async function* () {
+        yield {
+          candidates: [
+            { content: { role: 'model', parts: [{ text: 'Hello' }] } },
+          ],
+        } as unknown as GenerateContentResponse;
+        // FIX: The original test used { text: '' }, which is invalid.
+        // A chunk can be empty but still valid. This chunk is now removed
+        // as the important part is consolidating what comes after.
+        yield {
+          candidates: [
+            { content: { role: 'model', parts: [{ text: ' World!' }] } },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+
+      vi.mocked(mockModelsModule.generateContentStream).mockResolvedValue(
+        multiChunkStream,
+      );
+
+      // 2. Action: Send a message and consume the stream.
+      const stream = await chat.sendMessageStream(
+        { message: 'test message' },
+        'prompt-id-empty-chunk-consolidation',
+      );
+      for await (const _ of stream) {
+        // Consume the stream
+      }
+
+      // 3. Assert: Check that the final history was correctly consolidated.
+      const history = chat.getHistory();
+      expect(history.length).toBe(2);
+      const modelTurn = history[1]!;
+      expect(modelTurn?.parts?.length).toBe(1);
+      expect(modelTurn?.parts![0]!.text).toBe('Hello World!');
+    });
+
+    it('should consolidate adjacent text parts that arrive in separate stream chunks', async () => {
+      // 1. Mock the API to return a stream of multiple, adjacent text chunks.
+      const multiChunkStream = (async function* () {
+        yield {
+          candidates: [
+            { content: { role: 'model', parts: [{ text: 'This is the ' }] } },
+          ],
+        } as unknown as GenerateContentResponse;
+        yield {
+          candidates: [
+            { content: { role: 'model', parts: [{ text: 'first part.' }] } },
+          ],
+        } as unknown as GenerateContentResponse;
+        // This function call should break the consolidation.
+        yield {
+          candidates: [
+            {
+              content: {
+                role: 'model',
+                parts: [{ functionCall: { name: 'do_stuff', args: {} } }],
+              },
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+        yield {
+          candidates: [
+            {
+              content: {
+                role: 'model',
+                parts: [{ text: 'This is the second part.' }],
+              },
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+
+      vi.mocked(mockModelsModule.generateContentStream).mockResolvedValue(
+        multiChunkStream,
+      );
+
+      // 2. Action: Send a message and consume the stream.
+      const stream = await chat.sendMessageStream(
+        { message: 'test message' },
+        'prompt-id-multi-chunk',
+      );
+      for await (const _ of stream) {
+        // Consume the stream to trigger history recording.
+      }
+
+      // 3. Assert: Check that the final history was correctly consolidated.
+      const history = chat.getHistory();
+
+      // The history should contain the user's turn and ONE consolidated model turn.
+      expect(history.length).toBe(2);
+
+      const modelTurn = history[1]!;
+      expect(modelTurn.role).toBe('model');
+
+      // The model turn should have 3 distinct parts: the merged text, the function call, and the final text.
+      expect(modelTurn?.parts?.length).toBe(3);
+      expect(modelTurn?.parts![0]!.text).toBe('This is the first part.');
+      expect(modelTurn.parts![1]!.functionCall).toBeDefined();
+      expect(modelTurn.parts![2]!.text).toBe('This is the second part.');
+    });
+    it('should preserve text parts that stream in the same chunk as a thought', async () => {
+      // 1. Mock the API to return a single chunk containing both a thought and visible text.
+      const mixedContentStream = (async function* () {
+        yield {
+          candidates: [
+            {
+              content: {
+                role: 'model',
+                parts: [
+                  { thought: 'This is a thought.' },
+                  { text: 'This is the visible text that should not be lost.' },
+                ],
+              },
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+
+      vi.mocked(mockModelsModule.generateContentStream).mockResolvedValue(
+        mixedContentStream,
+      );
+
+      // 2. Action: Send a message and fully consume the stream to trigger history recording.
+      const stream = await chat.sendMessageStream(
+        { message: 'test message' },
+        'prompt-id-mixed-chunk',
+      );
+      for await (const _ of stream) {
+        // This loop consumes the stream.
+      }
+
+      // 3. Assert: Check the final state of the history.
+      const history = chat.getHistory();
+
+      // The history should contain two turns: the user's message and the model's response.
+      expect(history.length).toBe(2);
+
+      const modelTurn = history[1]!;
+      expect(modelTurn.role).toBe('model');
+
+      // CRUCIAL ASSERTION:
+      // The buggy code would fail here, resulting in parts.length being 0.
+      // The corrected code will pass, preserving the single visible text part.
+      expect(modelTurn?.parts?.length).toBe(1);
+      expect(modelTurn?.parts![0]!.text).toBe(
+        'This is the visible text that should not be lost.',
+      );
+    });
+    it('should add a placeholder model turn when a tool call is followed by an empty stream response', async () => {
+      // 1. Setup: A history where the model has just made a function call.
+      const initialHistory: Content[] = [
+        {
+          role: 'user',
+          parts: [{ text: 'Find a good Italian restaurant for me.' }],
+        },
+        {
+          role: 'model',
+          parts: [
+            {
+              functionCall: {
+                name: 'find_restaurant',
+                args: { cuisine: 'Italian' },
+              },
+            },
+          ],
+        },
+      ];
+      chat.setHistory(initialHistory);
+
+      // 2. Mock the API to return an empty/thought-only stream.
+      const emptyStreamResponse = (async function* () {
+        yield {
+          candidates: [
+            { content: { role: 'model', parts: [{ thought: true }] } },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+      vi.mocked(mockModelsModule.generateContentStream).mockResolvedValue(
+        emptyStreamResponse,
+      );
+
+      // 3. Action: Send the function response back to the model and consume the stream.
+      const stream = await chat.sendMessageStream(
+        {
+          message: {
+            functionResponse: {
+              name: 'find_restaurant',
+              response: { name: 'Vesuvio' },
+            },
+          },
+        },
+        'prompt-id-stream-1',
+      );
+      for await (const _ of stream) {
+        // This loop consumes the stream to trigger the internal logic.
+      }
+
+      // 4. Assert: The history should now have four valid, alternating turns.
+      const history = chat.getHistory();
+      expect(history.length).toBe(4);
+
+      // The final turn must be the empty model placeholder.
+      const lastTurn = history[3]!;
+      expect(lastTurn.role).toBe('model');
+      expect(lastTurn?.parts?.length).toBe(0);
+
+      // The second-to-last turn must be the function response we sent.
+      const secondToLastTurn = history[2]!;
+      expect(secondToLastTurn.role).toBe('user');
+      expect(secondToLastTurn?.parts![0]!.functionResponse).toBeDefined();
+    });
+
     it('should call generateContentStream with the correct parameters', async () => {
       const response = (async function* () {
         yield {
@@ -153,321 +565,145 @@ describe('GeminiChat', () => {
       parts: [{ text: 'User input' }],
     };
 
+    it('should consolidate all consecutive model turns into a single turn', () => {
+      const userInput: Content = {
+        role: 'user',
+        parts: [{ text: 'User input' }],
+      };
+      // This simulates a multi-part model response with different part types.
+      const modelOutput: Content[] = [
+        { role: 'model', parts: [{ text: 'Thinking...' }] },
+        {
+          role: 'model',
+          parts: [{ functionCall: { name: 'do_stuff', args: {} } }],
+        },
+      ];
+
+      // @ts-expect-error Accessing private method for testing
+      chat.recordHistory(userInput, modelOutput);
+      const history = chat.getHistory();
+
+      // The history should contain the user's turn and ONE consolidated model turn.
+      // The old code would fail here, resulting in a length of 3.
+      //expect(history).toBe([]);
+      expect(history.length).toBe(2);
+
+      const modelTurn = history[1]!;
+      expect(modelTurn.role).toBe('model');
+
+      // The consolidated turn should contain both the text part and the functionCall part.
+      expect(modelTurn?.parts?.length).toBe(2);
+      expect(modelTurn?.parts![0]!.text).toBe('Thinking...');
+      expect(modelTurn?.parts![1]!.functionCall).toBeDefined();
+    });
+
+    it('should add a placeholder model turn when a tool call is followed by an empty response', () => {
+      // 1. Setup: A history where the model has just made a function call.
+      const initialHistory: Content[] = [
+        { role: 'user', parts: [{ text: 'Initial prompt' }] },
+        {
+          role: 'model',
+          parts: [{ functionCall: { name: 'test_tool', args: {} } }],
+        },
+      ];
+      chat.setHistory(initialHistory);
+
+      // 2. Action: The user provides the tool's response, and the model's
+      // final output is empty (e.g., just a thought, which gets filtered out).
+      const functionResponse: Content = {
+        role: 'user',
+        parts: [{ functionResponse: { name: 'test_tool', response: {} } }],
+      };
+      const emptyModelOutput: Content[] = [];
+
+      // @ts-expect-error Accessing private method for testing
+      chat.recordHistory(functionResponse, emptyModelOutput, [
+        functionResponse,
+      ]);
+
+      // 3. Assert: The history should now have four valid, alternating turns.
+      const history = chat.getHistory();
+      expect(history.length).toBe(4);
+
+      // The final turn must be the empty model placeholder.
+      const lastTurn = history[3]!;
+      expect(lastTurn.role).toBe('model');
+      expect(lastTurn?.parts?.length).toBe(0);
+
+      // The second-to-last turn must be the function response we provided.
+      const secondToLastTurn = history[2]!;
+      expect(secondToLastTurn.role).toBe('user');
+      expect(secondToLastTurn?.parts![0]!.functionResponse).toBeDefined();
+    });
+
     it('should add user input and a single model output to history', () => {
       const modelOutput: Content[] = [
         { role: 'model', parts: [{ text: 'Model output' }] },
       ];
-      // @ts-expect-error Accessing private method for testing purposes
+      // @ts-expect-error Accessing private method for testing
       chat.recordHistory(userInput, modelOutput);
       const history = chat.getHistory();
-      expect(history).toEqual([userInput, modelOutput[0]]);
-    });
-
-    it('should consolidate adjacent model outputs', () => {
-      const modelOutputParts: Content[] = [
-        { role: 'model', parts: [{ text: 'Model part 1' }] },
-        { role: 'model', parts: [{ text: 'Model part 2' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputParts);
-      const history = chat.getHistory();
-      expect(history.length).toBe(2);
-      expect(history[0]).toEqual(userInput);
-      expect(history[1].role).toBe('model');
-      expect(history[1].parts).toEqual([{ text: 'Model part 1Model part 2' }]);
-    });
-
-    it('should handle a mix of user and model roles in outputContents (though unusual)', () => {
-      const mixedOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'Model 1' }] },
-        { role: 'user', parts: [{ text: 'Unexpected User' }] }, // This should be pushed as is
-        { role: 'model', parts: [{ text: 'Model 2' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, mixedOutput);
-      const history = chat.getHistory();
-      expect(history.length).toBe(4); // user, model1, user_unexpected, model2
-      expect(history[0]).toEqual(userInput);
-      expect(history[1]).toEqual(mixedOutput[0]);
-      expect(history[2]).toEqual(mixedOutput[1]);
-      expect(history[3]).toEqual(mixedOutput[2]);
-    });
-
-    it('should consolidate multiple adjacent model outputs correctly', () => {
-      const modelOutputParts: Content[] = [
-        { role: 'model', parts: [{ text: 'M1' }] },
-        { role: 'model', parts: [{ text: 'M2' }] },
-        { role: 'model', parts: [{ text: 'M3' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputParts);
-      const history = chat.getHistory();
-      expect(history.length).toBe(2);
-      expect(history[1].parts).toEqual([{ text: 'M1M2M3' }]);
-    });
-
-    it('should not consolidate if roles are different between model outputs', () => {
-      const modelOutputParts: Content[] = [
-        { role: 'model', parts: [{ text: 'M1' }] },
-        { role: 'user', parts: [{ text: 'Interjecting User' }] },
-        { role: 'model', parts: [{ text: 'M2' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputParts);
-      const history = chat.getHistory();
-      expect(history.length).toBe(4); // user, M1, Interjecting User, M2
-      expect(history[1].parts).toEqual([{ text: 'M1' }]);
-      expect(history[3].parts).toEqual([{ text: 'M2' }]);
-    });
-
-    it('should merge with last history entry if it is also a model output', () => {
-      // @ts-expect-error Accessing private property for test setup
-      chat.history = [
-        userInput,
-        { role: 'model', parts: [{ text: 'Initial Model Output' }] },
-      ]; // Prime the history
-
-      const newModelOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'New Model Part 1' }] },
-        { role: 'model', parts: [{ text: 'New Model Part 2' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, newModelOutput); // userInput here is for the *next* turn, but history is already primed
-
-      // Reset and set up a more realistic scenario for merging with existing history
-      chat = new GeminiChat(mockConfig, mockModelsModule, config, []);
-      const firstUserInput: Content = {
-        role: 'user',
-        parts: [{ text: 'First user input' }],
-      };
-      const firstModelOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'First model response' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(firstUserInput, firstModelOutput);
-
-      const secondUserInput: Content = {
-        role: 'user',
-        parts: [{ text: 'Second user input' }],
-      };
-      const secondModelOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'Second model response part 1' }] },
-        { role: 'model', parts: [{ text: 'Second model response part 2' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(secondUserInput, secondModelOutput);
-
-      const finalHistory = chat.getHistory();
-      expect(finalHistory.length).toBe(4); // user1, model1, user2, model2(consolidated)
-      expect(finalHistory[0]).toEqual(firstUserInput);
-      expect(finalHistory[1]).toEqual(firstModelOutput[0]);
-      expect(finalHistory[2]).toEqual(secondUserInput);
-      expect(finalHistory[3].role).toBe('model');
-      expect(finalHistory[3].parts).toEqual([
-        { text: 'Second model response part 1Second model response part 2' },
-      ]);
-    });
-
-    it('should correctly merge consolidated new output with existing model history', () => {
-      // Setup: history ends with a model turn
-      const initialUser: Content = {
-        role: 'user',
-        parts: [{ text: 'Initial user query' }],
-      };
-      const initialModel: Content = {
-        role: 'model',
-        parts: [{ text: 'Initial model answer.' }],
-      };
-      chat = new GeminiChat(mockConfig, mockModelsModule, config, [
-        initialUser,
-        initialModel,
-      ]);
-
-      // New interaction
-      const currentUserInput: Content = {
-        role: 'user',
-        parts: [{ text: 'Follow-up question' }],
-      };
-      const newModelParts: Content[] = [
-        { role: 'model', parts: [{ text: 'Part A of new answer.' }] },
-        { role: 'model', parts: [{ text: 'Part B of new answer.' }] },
-      ];
-
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(currentUserInput, newModelParts);
-      const history = chat.getHistory();
-
-      // Expected: initialUser, initialModel, currentUserInput, consolidatedNewModelParts
-      expect(history.length).toBe(4);
-      expect(history[0]).toEqual(initialUser);
-      expect(history[1]).toEqual(initialModel);
-      expect(history[2]).toEqual(currentUserInput);
-      expect(history[3].role).toBe('model');
-      expect(history[3].parts).toEqual([
-        { text: 'Part A of new answer.Part B of new answer.' },
-      ]);
-    });
-
-    it('should handle empty modelOutput array', () => {
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, []);
-      const history = chat.getHistory();
-      // If modelOutput is empty, it might push a default empty model part depending on isFunctionResponse
-      // Assuming isFunctionResponse(userInput) is false for this simple text input
-      expect(history.length).toBe(2);
-      expect(history[0]).toEqual(userInput);
-      expect(history[1].role).toBe('model');
-      expect(history[1].parts).toEqual([]);
-    });
-
-    it('should handle aggregating modelOutput', () => {
-      const modelOutputUndefinedParts: Content[] = [
-        { role: 'model', parts: [{ text: 'First model part' }] },
-        { role: 'model', parts: [{ text: 'Second model part' }] },
-        { role: 'model', parts: undefined as unknown as Part[] }, // Test undefined parts
-        { role: 'model', parts: [{ text: 'Third model part' }] },
-        { role: 'model', parts: [] }, // Test empty parts array
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputUndefinedParts);
-      const history = chat.getHistory();
-      expect(history.length).toBe(5);
-      expect(history[0]).toEqual(userInput);
-      expect(history[1].role).toBe('model');
-      expect(history[1].parts).toEqual([
-        { text: 'First model partSecond model part' },
-      ]);
-      expect(history[2].role).toBe('model');
-      expect(history[2].parts).toBeUndefined();
-      expect(history[3].role).toBe('model');
-      expect(history[3].parts).toEqual([{ text: 'Third model part' }]);
-      expect(history[4].role).toBe('model');
-      expect(history[4].parts).toEqual([]);
-    });
-
-    it('should handle modelOutput with parts being undefined or empty (if they pass initial every check)', () => {
-      const modelOutputUndefinedParts: Content[] = [
-        { role: 'model', parts: [{ text: 'Text part' }] },
-        { role: 'model', parts: undefined as unknown as Part[] }, // Test undefined parts
-        { role: 'model', parts: [] }, // Test empty parts array
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputUndefinedParts);
-      const history = chat.getHistory();
-      expect(history.length).toBe(4); // userInput, model1 (text), model2 (undefined parts), model3 (empty parts)
-      expect(history[0]).toEqual(userInput);
-      expect(history[1].role).toBe('model');
-      expect(history[1].parts).toEqual([{ text: 'Text part' }]);
-      expect(history[2].role).toBe('model');
-      expect(history[2].parts).toBeUndefined();
-      expect(history[3].role).toBe('model');
-      expect(history[3].parts).toEqual([]);
-    });
-
-    it('should correctly handle automaticFunctionCallingHistory', () => {
-      const afcHistory: Content[] = [
-        { role: 'user', parts: [{ text: 'AFC User' }] },
-        { role: 'model', parts: [{ text: 'AFC Model' }] },
-      ];
-      const modelOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'Regular Model Output' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutput, afcHistory);
-      const history = chat.getHistory();
-      expect(history.length).toBe(3);
-      expect(history[0]).toEqual(afcHistory[0]);
-      expect(history[1]).toEqual(afcHistory[1]);
-      expect(history[2]).toEqual(modelOutput[0]);
-    });
-
-    it('should add userInput if AFC history is present but empty', () => {
-      const modelOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'Model Output' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutput, []); // Empty AFC history
-      const history = chat.getHistory();
       expect(history.length).toBe(2);
       expect(history[0]).toEqual(userInput);
       expect(history[1]).toEqual(modelOutput[0]);
     });
 
-    it('should skip "thought" content from modelOutput', () => {
+    it('should consolidate adjacent text parts from multiple content objects', () => {
-      const modelOutputWithThought: Content[] = [
+      const modelOutput: Content[] = [
-        { role: 'model', parts: [{ thought: true }, { text: 'Visible text' }] },
-        { role: 'model', parts: [{ text: 'Another visible text' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputWithThought);
-      const history = chat.getHistory();
-      expect(history.length).toBe(2); // User input + consolidated model output
-      expect(history[0]).toEqual(userInput);
-      expect(history[1].role).toBe('model');
-      // The 'thought' part is skipped, 'Another visible text' becomes the first part.
-      expect(history[1].parts).toEqual([{ text: 'Another visible text' }]);
-    });
-
-    it('should skip "thought" content even if it is the only content', () => {
-      const modelOutputOnlyThought: Content[] = [
-        { role: 'model', parts: [{ thought: true }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputOnlyThought);
-      const history = chat.getHistory();
-      expect(history.length).toBe(1); // User input + default empty model part
-      expect(history[0]).toEqual(userInput);
-    });
-
-    it('should correctly consolidate text parts when a thought part is in between', () => {
-      const modelOutputMixed: Content[] = [
         { role: 'model', parts: [{ text: 'Part 1.' }] },
-        {
+        { role: 'model', parts: [{ text: ' Part 2.' }] },
-          role: 'model',
+        { role: 'model', parts: [{ text: ' Part 3.' }] },
-          parts: [{ thought: true }, { text: 'Should be skipped' }],
-        },
-        { role: 'model', parts: [{ text: 'Part 2.' }] },
       ];
-      // @ts-expect-error Accessing private method for testing purposes
+      // @ts-expect-error Accessing private method for testing
-      chat.recordHistory(userInput, modelOutputMixed);
+      chat.recordHistory(userInput, modelOutput);
       const history = chat.getHistory();
       expect(history.length).toBe(2);
-      expect(history[0]).toEqual(userInput);
+      expect(history[1]!.role).toBe('model');
-      expect(history[1].role).toBe('model');
+      expect(history[1]!.parts).toEqual([{ text: 'Part 1. Part 2. Part 3.' }]);
-      expect(history[1].parts).toEqual([{ text: 'Part 1.Part 2.' }]);
     });
 
-    it('should handle multiple thought parts correctly', () => {
+    it('should add an empty placeholder turn if modelOutput is empty', () => {
-      const modelOutputMultipleThoughts: Content[] = [
+      // This simulates receiving a pre-filtered, thought-only response.
-        { role: 'model', parts: [{ thought: true }] },
+      const emptyModelOutput: Content[] = [];
-        { role: 'model', parts: [{ text: 'Visible 1' }] },
+      // @ts-expect-error Accessing private method for testing
-        { role: 'model', parts: [{ thought: true }] },
+      chat.recordHistory(userInput, emptyModelOutput);
-        { role: 'model', parts: [{ text: 'Visible 2' }] },
-      ];
-      // @ts-expect-error Accessing private method for testing purposes
-      chat.recordHistory(userInput, modelOutputMultipleThoughts);
       const history = chat.getHistory();
       expect(history.length).toBe(2);
       expect(history[0]).toEqual(userInput);
-      expect(history[1].role).toBe('model');
+      expect(history[1]!.role).toBe('model');
-      expect(history[1].parts).toEqual([{ text: 'Visible 1Visible 2' }]);
+      expect(history[1]!.parts).toEqual([]);
     });
 
-    it('should handle thought part at the end of outputContents', () => {
+    it('should preserve model outputs with undefined or empty parts arrays', () => {
-      const modelOutputThoughtAtEnd: Content[] = [
+      const malformedOutput: Content[] = [
-        { role: 'model', parts: [{ text: 'Visible text' }] },
+        { role: 'model', parts: [{ text: 'Text part' }] },
-        { role: 'model', parts: [{ thought: true }] },
+        { role: 'model', parts: undefined as unknown as Part[] },
+        { role: 'model', parts: [] },
       ];
-      // @ts-expect-error Accessing private method for testing purposes
+      // @ts-expect-error Accessing private method for testing
-      chat.recordHistory(userInput, modelOutputThoughtAtEnd);
+      chat.recordHistory(userInput, malformedOutput);
       const history = chat.getHistory();
-      expect(history.length).toBe(2);
+      expect(history.length).toBe(4); // userInput + 3 model turns
-      expect(history[0]).toEqual(userInput);
+      expect(history[1]!.parts).toEqual([{ text: 'Text part' }]);
-      expect(history[1].role).toBe('model');
+      expect(history[2]!.parts).toBeUndefined();
-      expect(history[1].parts).toEqual([{ text: 'Visible text' }]);
+      expect(history[3]!.parts).toEqual([]);
+    });
+
+    it('should not consolidate content with different roles', () => {
+      const mixedOutput: Content[] = [
+        { role: 'model', parts: [{ text: 'Model 1' }] },
+        { role: 'user', parts: [{ text: 'Unexpected User' }] },
+        { role: 'model', parts: [{ text: 'Model 2' }] },
+      ];
+      // @ts-expect-error Accessing private method for testing
+      chat.recordHistory(userInput, mixedOutput);
+      const history = chat.getHistory();
+      expect(history.length).toBe(4); // userInput, model1, unexpected_user, model2
+      expect(history[1]).toEqual(mixedOutput[0]);
+      expect(history[2]).toEqual(mixedOutput[1]);
+      expect(history[3]).toEqual(mixedOutput[2]);
     });
   });
-
   describe('addHistory', () => {
     it('should add a new content item to the history', () => {
       const newContent: Content = {

packages/core/src/core/geminiChat.ts

@@ -17,7 +17,6 @@ import type {
 } from '@google/genai';
 import { createUserContent } from '@google/genai';
 import { retryWithBackoff } from '../utils/retry.js';
-import { isFunctionResponse } from '../utils/messageInspectors.js';
 import type { ContentGenerator } from './contentGenerator.js';
 import { AuthType } from './contentGenerator.js';
 import type { Config } from '../config/config.js';
@@ -44,6 +43,7 @@ const INVALID_CONTENT_RETRY_OPTIONS: ContentRetryOptions = {
   maxAttempts: 3, // 1 initial call + 2 retries
   initialDelayMs: 500,
 };
+
 /**
  * Returns true if the response is valid, false otherwise.
  */
@@ -221,7 +221,7 @@ export class GeminiChat {
    * ```ts
    * const chat = ai.chats.create({model: 'gemini-2.0-flash'});
    * const response = await chat.sendMessage({
-   *   message: 'Why is the sky blue?'
+   * message: 'Why is the sky blue?'
    * });
    * console.log(response.text);
    * ```
@@ -277,6 +277,8 @@ export class GeminiChat {
 
       this.sendPromise = (async () => {
         const outputContent = response.candidates?.[0]?.content;
+        const modelOutput = outputContent ? [outputContent] : [];
+
         // Because the AFC input contains the entire curated chat history in
         // addition to the new user input, we need to truncate the AFC history
         // to deduplicate the existing chat history.
@@ -288,16 +290,18 @@ export class GeminiChat {
           automaticFunctionCallingHistory =
             fullAutomaticFunctionCallingHistory.slice(index) ?? [];
         }
-        const modelOutput = outputContent ? [outputContent] : [];
+
         this.recordHistory(
           userContent,
           modelOutput,
           automaticFunctionCallingHistory,
         );
       })();
-      await this.sendPromise.catch(() => {
+      await this.sendPromise.catch((error) => {
         // Resets sendPromise to avoid subsequent calls failing
         this.sendPromise = Promise.resolve();
+        // Re-throw the error so the caller knows something went wrong.
+        throw error;
       });
       return response;
     } catch (error) {
@@ -321,10 +325,10 @@ export class GeminiChat {
    * ```ts
    * const chat = ai.chats.create({model: 'gemini-2.0-flash'});
    * const response = await chat.sendMessageStream({
-   *   message: 'Why is the sky blue?'
+   * message: 'Why is the sky blue?'
    * });
    * for await (const chunk of response) {
-   *   console.log(chunk.text);
+   * console.log(chunk.text);
    * }
    * ```
    */
@@ -464,7 +468,7 @@ export class GeminiChat {
    * - The `curated history` contains only the valid turns between user and
    * model, which will be included in the subsequent requests sent to the model.
    * - The `comprehensive history` contains all turns, including invalid or
-   *   empty model outputs, providing a complete record of the history.
+   * empty model outputs, providing a complete record of the history.
    *
    * The history is updated after receiving the response from the model,
    * for streaming response, it means receiving the last chunk of the response.
@@ -473,9 +477,9 @@ export class GeminiChat {
    * history`, set the `curated` parameter to `true`.
    *
    * @param curated - whether to return the curated history or the comprehensive
-   *     history.
+   * history.
    * @return History contents alternating between user and model for the entire
-   *     chat session.
+   * chat session.
    */
   getHistory(curated: boolean = false): Content[] {
     const history = curated
@@ -547,31 +551,29 @@ export class GeminiChat {
       hasReceivedAnyChunk = true;
       if (isValidResponse(chunk)) {
         const content = chunk.candidates?.[0]?.content;
-        if (content) {
+        if (content?.parts) {
-          // Filter out thought parts from being added to history.
+          modelResponseParts.push(...content.parts);
-          if (!this.isThoughtContent(content) && content.parts) {
-            modelResponseParts.push(...content.parts);
-          }
         }
       } else {
         recordInvalidChunk(this.config);
         isStreamInvalid = true;
       }
-      yield chunk; // Yield every chunk to the UI immediately.
+      yield chunk;
     }
 
-    // Now that the stream is finished, make a decision.
-    // Throw an error if the stream was invalid OR if it was completely empty.
     if (isStreamInvalid || !hasReceivedAnyChunk) {
       throw new EmptyStreamError(
         'Model stream was invalid or completed without valid content.',
       );
     }
 
-    // Use recordHistory to correctly save the conversation turn.
+    // Bundle all streamed parts into a single Content object
-    const modelOutput: Content[] = [
+    const modelOutput: Content[] =
-      { role: 'model', parts: modelResponseParts },
+      modelResponseParts.length > 0
-    ];
+        ? [{ role: 'model', parts: modelResponseParts }]
+        : [];
+
+    // Pass the raw, bundled data to the new, robust recordHistory
     this.recordHistory(userInput, modelOutput);
   }
 
@@ -580,91 +582,101 @@ export class GeminiChat {
     modelOutput: Content[],
     automaticFunctionCallingHistory?: Content[],
   ) {
-    const newHistoryEntries: Content[] = [];
+    // Part 1: Handle the user's turn.
-
-    // Part 1: Handle the user's part of the turn.
     if (
       automaticFunctionCallingHistory &&
       automaticFunctionCallingHistory.length > 0
     ) {
-      newHistoryEntries.push(
+      this.history.push(
         ...extractCuratedHistory(automaticFunctionCallingHistory),
       );
     } else {
-      // Guard for streaming calls where the user input might already be in the history.
       if (
         this.history.length === 0 ||
         this.history[this.history.length - 1] !== userInput
       ) {
-        newHistoryEntries.push(userInput);
+        const lastTurn = this.history[this.history.length - 1];
-      }
+        // The only time we don't push is if it's the *exact same* object,
-    }
+        // which happens in streaming where we add it preemptively.
-
+        if (lastTurn !== userInput) {
-    // Part 2: Handle the model's part of the turn, filtering out thoughts.
+          if (lastTurn?.role === 'user') {
-    const nonThoughtModelOutput = modelOutput.filter(
+            // This is an invalid sequence.
-      (content) => !this.isThoughtContent(content),
+            throw new Error('Cannot add a user turn after another user turn.');
-    );
-
-    let outputContents: Content[] = [];
-    if (nonThoughtModelOutput.length > 0) {
-      outputContents = nonThoughtModelOutput;
-    } else if (
-      modelOutput.length === 0 &&
-      !isFunctionResponse(userInput) &&
-      !automaticFunctionCallingHistory
-    ) {
-      // Add an empty model response if the model truly returned nothing.
-      outputContents.push({ role: 'model', parts: [] } as Content);
-    }
-
-    // Part 3: Consolidate the parts of this turn's model response.
-    const consolidatedOutputContents: Content[] = [];
-    if (outputContents.length > 0) {
-      for (const content of outputContents) {
-        const lastContent =
-          consolidatedOutputContents[consolidatedOutputContents.length - 1];
-        if (this.hasTextContent(lastContent) && this.hasTextContent(content)) {
-          lastContent.parts[0].text += content.parts[0].text || '';
-          if (content.parts.length > 1) {
-            lastContent.parts.push(...content.parts.slice(1));
           }
-        } else {
+          this.history.push(userInput);
-          consolidatedOutputContents.push(content);
         }
       }
     }
 
-    // Part 4: Add the new turn (user and model parts) to the main history.
+    // Part 2: Process the model output into a final, consolidated list of turns.
-    this.history.push(...newHistoryEntries, ...consolidatedOutputContents);
+    const finalModelTurns: Content[] = [];
-  }
+    for (const content of modelOutput) {
+      // A. Preserve malformed content that has no 'parts' array.
+      if (!content.parts) {
+        finalModelTurns.push(content);
+        continue;
+      }
 
-  private hasTextContent(
+      // B. Filter out 'thought' parts.
-    content: Content | undefined,
+      const visibleParts = content.parts.filter((part) => !part.thought);
-  ): content is Content & { parts: [{ text: string }, ...Part[]] } {
-    return !!(
-      content &&
-      content.role === 'model' &&
-      content.parts &&
-      content.parts.length > 0 &&
-      typeof content.parts[0].text === 'string' &&
-      content.parts[0].text !== ''
-    );
-  }
 
-  private isThoughtContent(
+      const newTurn = { ...content, parts: visibleParts };
-    content: Content | undefined,
+      const lastTurnInFinal = finalModelTurns[finalModelTurns.length - 1];
-  ): content is Content & { parts: [{ thought: boolean }, ...Part[]] } {
+
-    return !!(
+      // Consolidate this new turn with the PREVIOUS turn if they are adjacent model turns.
-      content &&
+      if (
-      content.role === 'model' &&
+        lastTurnInFinal &&
-      content.parts &&
+        lastTurnInFinal.role === 'model' &&
-      content.parts.length > 0 &&
+        newTurn.role === 'model' &&
-      typeof content.parts[0].thought === 'boolean' &&
+        lastTurnInFinal.parts && // SAFETY CHECK: Ensure the destination has a parts array.
-      content.parts[0].thought === true
+        newTurn.parts
-    );
+      ) {
+        lastTurnInFinal.parts.push(...newTurn.parts);
+      } else {
+        finalModelTurns.push(newTurn);
+      }
+    }
+
+    // Part 3: Add the processed model turns to the history, with one final consolidation pass.
+    if (finalModelTurns.length > 0) {
+      // Re-consolidate parts within any turns that were merged in the previous step.
+      for (const turn of finalModelTurns) {
+        if (turn.parts && turn.parts.length > 1) {
+          const consolidatedParts: Part[] = [];
+          for (const part of turn.parts) {
+            const lastPart = consolidatedParts[consolidatedParts.length - 1];
+            if (
+              lastPart &&
+              // Ensure lastPart is a pure text part
+              typeof lastPart.text === 'string' &&
+              !lastPart.functionCall &&
+              !lastPart.functionResponse &&
+              !lastPart.inlineData &&
+              !lastPart.fileData &&
+              !lastPart.thought &&
+              // Ensure current part is a pure text part
+              typeof part.text === 'string' &&
+              !part.functionCall &&
+              !part.functionResponse &&
+              !part.inlineData &&
+              !part.fileData &&
+              !part.thought
+            ) {
+              lastPart.text += part.text;
+            } else {
+              consolidatedParts.push({ ...part });
+            }
+          }
+          turn.parts = consolidatedParts;
+        }
+      }
+      this.history.push(...finalModelTurns);
+    } else {
+      // If, after all processing, there's NO model output, add the placeholder.
+      this.history.push({ role: 'model', parts: [] });
+    }
   }
 }
-
 /** Visible for Testing */
 export function isSchemaDepthError(errorMessage: string): boolean {
   return errorMessage.includes('maximum schema depth exceeded');