fix(core): filter out thought parts from getHistoryTurns when context management is disabled

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

@@ -2282,6 +2282,62 @@
         text: 'actual conversational response',
       });
     });
+
+    it('should completely filter out thought parts from getHistoryTurns when context management is disabled but model is gemini-2/modern', () => {
+      vi.mocked(mockConfig.isContextManagementEnabled).mockReturnValue(false);
+      vi.mocked(mockConfig.getModel).mockReturnValue('gemini-2.5-pro');
+
+      chat.setHistory([
+        {
+          role: 'user',
+          parts: [{ text: 'hello' }],
+        },
+        {
+          role: 'model',
+          parts: [
+            { text: 'internal monologue', thought: true } as unknown as Part,
+            { text: 'actual conversational response' },
+          ],
+        },
+      ]);
+
+      const turns = chat.getHistoryTurns(true);
+
+      expect(turns).toHaveLength(2);
+      const modelTurn = turns[1];
+      expect(modelTurn.content.parts).toHaveLength(1);
+      expect(modelTurn.content.parts![0]).toEqual({
+        text: 'actual conversational response',
+      });
+    });
+
+    it('should completely filter out thought parts from getHistoryTurns when model supports modern features', () => {
+      vi.mocked(mockConfig.isContextManagementEnabled).mockReturnValue(false);
+      vi.mocked(mockConfig.getModel).mockReturnValue('gemini-3.1-pro-preview');
+
+      chat.setHistory([
+        {
+          role: 'user',
+          parts: [{ text: 'hello' }],
+        },
+        {
+          role: 'model',
+          parts: [
+            { text: 'internal monologue', thought: true } as unknown as Part,
+            { text: 'actual conversational response' },
+          ],
+        },
+      ]);
+
+      const turns = chat.getHistoryTurns(true);
+
+      expect(turns).toHaveLength(2);
+      const modelTurn = turns[1];
+      expect(modelTurn.content.parts).toHaveLength(1);
+      expect(modelTurn.content.parts![0]).toEqual({
+        text: 'actual conversational response',
+      });
+    });
   });
 
   describe('ensureActiveLoopHasThoughtSignatures', () => {

packages/core/src/core/geminiChat.ts

@@ -30,7 +30,11 @@ import {
   getRetryErrorType,
 } from '../utils/retry.js';
 import type { ValidationRequiredError } from '../utils/googleQuotaErrors.js';
-import { resolveModel, supportsModernFeatures } from '../config/models.js';
+import {
+  resolveModel,
+  supportsModernFeatures,
+  isGemini2Model,
+} from '../config/models.js';
 import { hasCycleInSchema } from '../tools/tools.js';
 import type { StructuredError } from './turn.js';
 import type { CompletedToolCall } from '../scheduler/types.js';
@@ -766,9 +770,10 @@ export class GeminiChat {
         abortSignal,
       };
 
-      let contentsToUse: Content[] = supportsModernFeatures(modelToUse)
-        ? [...contentsForPreviewModel]
-        : [...requestContents];
+      let contentsToUse: Content[] =
+        supportsModernFeatures(modelToUse) || isGemini2Model(modelToUse)
+          ? [...contentsForPreviewModel]
+          : [...requestContents];
 
       const hookSystem = this.context.config.getHookSystem();
       if (hookSystem) {
@@ -810,9 +815,10 @@ export class GeminiChat {
           );
           lastModelToUse = modelToUse;
           // Re-evaluate contentsToUse based on the new model's feature support
-          contentsToUse = supportsModernFeatures(modelToUse)
-            ? [...contentsForPreviewModel]
-            : [...requestContents];
+          contentsToUse =
+            supportsModernFeatures(modelToUse) || isGemini2Model(modelToUse)
+              ? [...contentsForPreviewModel]
+              : [...requestContents];
         }
         if (beforeModelResult.modifiedConfig) {
           Object.assign(config, beforeModelResult.modifiedConfig);
@@ -956,9 +962,16 @@ export class GeminiChat {
       ? extractCuratedHistory(this.agentHistory.get())
       : [...this.agentHistory.get()];
 
-    return this.context.config.isContextManagementEnabled()
-      ? scrubHistory(history)
-      : history;
+    if (this.context.config.isContextManagementEnabled()) {
+      return scrubHistory(history);
+    }
+
+    const model = this.context.config.getModel();
+    if (isGemini2Model(model) || supportsModernFeatures(model)) {
+      return stripThoughts(history);
+    }
+
+    return history;
   }
 
   /**
@@ -1503,3 +1516,20 @@ export function coalesceConsecutiveRoles(
   }
   return result;
 }
+
+export function stripThoughts(history: HistoryTurn[]): HistoryTurn[] {
+  return history.map((turn) => {
+    if (!turn.content.parts) return turn;
+    const hasThought = turn.content.parts.some((p) => p && p.thought);
+    if (!hasThought) return turn;
+
+    const nonThoughtParts = turn.content.parts.filter((p) => p && !p.thought);
+    return {
+      id: turn.id,
+      content: {
+        ...turn.content,
+        parts: nonThoughtParts,
+      },
+    };
+  });
+}