fix(core): flush transcript for pure tool-call responses to ensure BeforeTool hooks see complete state (#20419)

Co-authored-by: Bryan Morgan <bryanmorgan@google.com>

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

@@ -1032,6 +1032,59 @@ describe('GeminiChat', () => {
         LlmRole.MAIN,
       );
     });
+
+    it('should flush transcript before tool dispatch for pure tool call with no text or thoughts', async () => {
+      const pureToolCallStream = (async function* () {
+        yield {
+          candidates: [
+            {
+              content: {
+                role: 'model',
+                parts: [
+                  {
+                    functionCall: {
+                      name: 'read_file',
+                      args: { path: 'test.py' },
+                    },
+                  },
+                ],
+              },
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+
+      vi.mocked(mockContentGenerator.generateContentStream).mockResolvedValue(
+        pureToolCallStream,
+      );
+
+      const { default: fs } = await import('node:fs');
+      const writeFileSync = vi.mocked(fs.writeFileSync);
+      const writeCountBefore = writeFileSync.mock.calls.length;
+
+      const stream = await chat.sendMessageStream(
+        { model: 'test-model' },
+        'analyze test.py',
+        'prompt-id-pure-tool-flush',
+        new AbortController().signal,
+        LlmRole.MAIN,
+      );
+      for await (const _ of stream) {
+        // consume
+      }
+
+      const newWrites = writeFileSync.mock.calls.slice(writeCountBefore);
+      expect(newWrites.length).toBeGreaterThan(0);
+
+      const lastWriteData = JSON.parse(
+        newWrites[newWrites.length - 1][1] as string,
+      ) as { messages: Array<{ type: string }> };
+
+      const geminiMessages = lastWriteData.messages.filter(
+        (m) => m.type === 'gemini',
+      );
+      expect(geminiMessages.length).toBeGreaterThan(0);
+    });
   });
 
   describe('addHistory', () => {

packages/core/src/core/geminiChat.ts

@@ -818,6 +818,7 @@ export class GeminiChat {
     const modelResponseParts: Part[] = [];
 
     let hasToolCall = false;
+    let hasThoughts = false;
     let finishReason: FinishReason | undefined;
 
     for await (const chunk of streamResponse) {
@@ -834,6 +835,7 @@ export class GeminiChat {
         if (content?.parts) {
           if (content.parts.some((part) => part.thought)) {
             // Record thoughts
+            hasThoughts = true;
             this.recordThoughtFromContent(content);
           }
           if (content.parts.some((part) => part.functionCall)) {
@@ -901,8 +903,10 @@ export class GeminiChat {
       .join('')
       .trim();
 
-    // Record model response text from the collected parts
+    // Record model response text from the collected parts.
-    if (responseText) {
+    // Also flush when there are thoughts or a tool call (even with no text)
+    // so that BeforeTool hooks always see the latest transcript state.
+    if (responseText || hasThoughts || hasToolCall) {
       this.chatRecordingService.recordMessage({
         model,
         type: 'gemini',