From 0a6f2e089f5f5aa1bbdedc4681b9adecf60bacc4 Mon Sep 17 00:00:00 2001
From: Pyry Takala <7336413+pyrytakala@users.noreply.github.com>
Date: Mon, 19 Jan 2026 13:04:45 -0800
Subject: [PATCH] Fix: Process all parts in response chunks when thought is
 first (#13539)

---
 packages/core/src/core/turn.test.ts  | 102 +++++++++++++++++++++++++++
 packages/core/src/core/turn.ts       |  19 ++---
 packages/core/src/utils/partUtils.ts |   2 +-
 3 files changed, 113 insertions(+), 10 deletions(-)

diff --git a/packages/core/src/core/turn.test.ts b/packages/core/src/core/turn.test.ts
index e951d80933..43146e31ec 100644
--- a/packages/core/src/core/turn.test.ts
+++ b/packages/core/src/core/turn.test.ts
@@ -754,6 +754,108 @@ describe('Turn', () => {
 
       expect(events).toEqual([expectedEvent]);
     });
+
+    it('should process all parts when thought is first part in chunk', async () => {
+      const mockResponseStream = (async function* () {
+        yield {
+          type: StreamEventType.CHUNK,
+          value: {
+            candidates: [
+              {
+                content: {
+                  parts: [
+                    { text: '**Planning** the solution', thought: 'planning' },
+                    { text: 'I will help you with that.' },
+                  ],
+                },
+                citationMetadata: {
+                  citations: [{ uri: 'https://example.com', title: 'Source' }],
+                },
+                finishReason: 'STOP',
+              },
+            ],
+            functionCalls: [
+              {
+                id: 'fc1',
+                name: 'ReadFile',
+                args: { path: 'file.txt' },
+              },
+            ],
+            responseId: 'trace-789',
+          } as unknown as GenerateContentResponse,
+        };
+      })();
+      mockSendMessageStream.mockResolvedValue(mockResponseStream);
+
+      const events = [];
+      for await (const event of turn.run(
+        { model: 'gemini' },
+        [{ text: 'Test mixed content' }],
+        new AbortController().signal,
+      )) {
+        events.push(event);
+      }
+
+      // Should yield:
+      // 1. Thought event (from first part)
+      // 2. Content event (from second part)
+      // 3. ToolCallRequest event (from functionCalls)
+      // 4. Citation event (from citationMetadata, emitted with finishReason)
+      // 5. Finished event (from finishReason)
+
+      expect(events.length).toBe(5);
+
+      const thoughtEvent = events.find(
+        (e) => e.type === GeminiEventType.Thought,
+      );
+      expect(thoughtEvent).toBeDefined();
+      expect(thoughtEvent).toMatchObject({
+        type: GeminiEventType.Thought,
+        value: { subject: 'Planning', description: 'the solution' },
+        traceId: 'trace-789',
+      });
+
+      const contentEvent = events.find(
+        (e) => e.type === GeminiEventType.Content,
+      );
+      expect(contentEvent).toBeDefined();
+      expect(contentEvent).toMatchObject({
+        type: GeminiEventType.Content,
+        value: 'I will help you with that.',
+        traceId: 'trace-789',
+      });
+
+      const toolCallEvent = events.find(
+        (e) => e.type === GeminiEventType.ToolCallRequest,
+      );
+      expect(toolCallEvent).toBeDefined();
+      expect(toolCallEvent).toMatchObject({
+        type: GeminiEventType.ToolCallRequest,
+        value: expect.objectContaining({
+          callId: 'fc1',
+          name: 'ReadFile',
+          args: { path: 'file.txt' },
+        }),
+      });
+
+      const citationEvent = events.find(
+        (e) => e.type === GeminiEventType.Citation,
+      );
+      expect(citationEvent).toBeDefined();
+      expect(citationEvent).toMatchObject({
+        type: GeminiEventType.Citation,
+        value: expect.stringContaining('https://example.com'),
+      });
+
+      const finishedEvent = events.find(
+        (e) => e.type === GeminiEventType.Finished,
+      );
+      expect(finishedEvent).toBeDefined();
+      expect(finishedEvent).toMatchObject({
+        type: GeminiEventType.Finished,
+        value: { reason: 'STOP' },
+      });
+    });
   });
 
   describe('getDebugResponses', () => {
diff --git a/packages/core/src/core/turn.ts b/packages/core/src/core/turn.ts
index 90d6a3cbfc..7ecd01340d 100644
--- a/packages/core/src/core/turn.ts
+++ b/packages/core/src/core/turn.ts
@@ -290,15 +290,16 @@ export class Turn {
 
         const traceId = resp.responseId;
 
-        const thoughtPart = resp.candidates?.[0]?.content?.parts?.[0];
-        if (thoughtPart?.thought) {
-          const thought = parseThought(thoughtPart.text ?? '');
-          yield {
-            type: GeminiEventType.Thought,
-            value: thought,
-            traceId,
-          };
-          continue;
+        const parts = resp.candidates?.[0]?.content?.parts ?? [];
+        for (const part of parts) {
+          if (part.thought) {
+            const thought = parseThought(part.text ?? '');
+            yield {
+              type: GeminiEventType.Thought,
+              value: thought,
+              traceId,
+            };
+          }
         }
 
         const text = getResponseText(resp);
diff --git a/packages/core/src/utils/partUtils.ts b/packages/core/src/utils/partUtils.ts
index f5195c11ca..5afa60d5b5 100644
--- a/packages/core/src/utils/partUtils.ts
+++ b/packages/core/src/utils/partUtils.ts
@@ -81,7 +81,7 @@ export function getResponseText(
       candidate.content.parts.length > 0
     ) {
       return candidate.content.parts
-        .filter((part) => part.text)
+        .filter((part) => part.text && !part.thought)
         .map((part) => part.text)
         .join('');
     }