fix(core): set temperature to 1 on retry in sendMessageStream (#10866)

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

@@ -864,6 +864,72 @@ describe('GeminiChat', () => {
       expect(uiTelemetryService.setLastPromptTokenCount).not.toHaveBeenCalled();
     });
 
+    it('should set temperature to 1 on retry', async () => {
+      // Use mockImplementationOnce to provide a fresh, promise-wrapped generator for each attempt.
+      vi.mocked(mockContentGenerator.generateContentStream)
+        .mockImplementationOnce(async () =>
+          // First call returns an invalid stream
+          (async function* () {
+            yield {
+              candidates: [{ content: { parts: [{ text: '' }] } }], // Invalid empty text part
+            } as unknown as GenerateContentResponse;
+          })(),
+        )
+        .mockImplementationOnce(async () =>
+          // Second call returns a valid stream
+          (async function* () {
+            yield {
+              candidates: [
+                {
+                  content: { parts: [{ text: 'Successful response' }] },
+                  finishReason: 'STOP',
+                },
+              ],
+            } as unknown as GenerateContentResponse;
+          })(),
+        );
+
+      const stream = await chat.sendMessageStream(
+        'test-model',
+        { message: 'test', config: { temperature: 0.5 } },
+        'prompt-id-retry-temperature',
+      );
+
+      for await (const _ of stream) {
+        // consume stream
+      }
+
+      expect(mockContentGenerator.generateContentStream).toHaveBeenCalledTimes(
+        2,
+      );
+
+      // First call should have original temperature
+      expect(
+        mockContentGenerator.generateContentStream,
+      ).toHaveBeenNthCalledWith(
+        1,
+        expect.objectContaining({
+          config: expect.objectContaining({
+            temperature: 0.5,
+          }),
+        }),
+        'prompt-id-retry-temperature',
+      );
+
+      // Second call (retry) should have temperature 1
+      expect(
+        mockContentGenerator.generateContentStream,
+      ).toHaveBeenNthCalledWith(
+        2,
+        expect.objectContaining({
+          config: expect.objectContaining({
+            temperature: 1,
+          }),
+        }),
+        'prompt-id-retry-temperature',
+      );
+    });
+
     it('should fail after all retries on persistent invalid content and report metrics', async () => {
       vi.mocked(mockContentGenerator.generateContentStream).mockImplementation(
         async () =>

packages/core/src/core/geminiChat.ts

@@ -273,10 +273,19 @@ export class GeminiChat {
               yield { type: StreamEventType.RETRY };
             }
 
+            // If this is a retry, set temperature to 1 to encourage different output.
+            const currentParams = { ...params };
+            if (attempt > 0) {
+              currentParams.config = {
+                ...currentParams.config,
+                temperature: 1,
+              };
+            }
+
             const stream = await self.makeApiCallAndProcessStream(
               model,
               requestContents,
-              params,
+              currentParams,
               prompt_id,
             );