fix(antigravity): default includeThoughts for modern Gemini models (#4180)

Integrated into release/v3.8.29 — default includeThoughts for modern Gemini (2.5+) in the openai->gemini translator, so the model's reasoning is marked thought:true and routed to reasoning_content instead of leaking into visible content (#4170). Thanks @dhaern! On review we regenerated the gemini golden snapshots (basic-chat/with-system) and committed the new modern-gemini-default-thinking snapshot. 61/61 translator + golden tests pass; eslint clean. Respects explicit client thinking config (only applies when none is set) and excludes gemini-1.x / non-thinking 2.0.

open-sse/translator/request/openai-to-gemini.ts

@@ -307,6 +307,26 @@ function openaiToGeminiBase(
     };
   }
 
+  // 3. Default: all modern Gemini models (2.5+) have thinking capability.
+  // If the client didn't explicitly request thinking (via reasoning_effort or
+  // thinking.type), still set includeThoughts so the upstream marks thought
+  // parts with thought:true. Without this, the model's reasoning leaks into
+  // visible content instead of being routed to reasoning_content by the
+  // response translator. (#4170)
+  if (!result.generationConfig.thinkingConfig) {
+    const modelLower = model.toLowerCase();
+    if (
+      modelLower.includes("gemini") &&
+      !modelLower.includes("gemini-1") &&
+      (!modelLower.includes("gemini-2.0") || modelLower.includes("thinking"))
+    ) {
+      result.generationConfig.thinkingConfig = {
+        thinkingBudget: getDefaultThinkingBudget(model) || capThinkingBudget(model, 24576),
+        includeThoughts: true,
+      };
+    }
+  }
+
   // Build tool_call_id -> name map
   const tcID2Name: Record<string, string> = {};
   const messages = body.messages as Array<Record<string, unknown>> | undefined;

tests/fixtures/translation/openai-to-gemini.json

@@ -5,7 +5,12 @@
     "targetFormat": "gemini",
     "input": {
       "model": "gemini-2.5-flash",
-      "messages": [{ "role": "user", "content": "Hello Gemini!" }]
+      "messages": [
+        {
+          "role": "user",
+          "content": "Hello Gemini!"
+        }
+      ]
     }
   },
   {
@@ -15,10 +20,30 @@
     "input": {
       "model": "gemini-2.5-pro",
       "messages": [
-        { "role": "system", "content": "You are a helpful assistant." },
-        { "role": "user", "content": "Tell me a joke." }
+        {
+          "role": "system",
+          "content": "You are a helpful assistant."
+        },
+        {
+          "role": "user",
+          "content": "Tell me a joke."
+        }
       ],
       "temperature": 0.7
     }
+  },
+  {
+    "name": "openai-to-gemini/modern-gemini-default-thinking",
+    "sourceFormat": "openai",
+    "targetFormat": "gemini",
+    "input": {
+      "model": "gemini-2.5-flash",
+      "messages": [
+        {
+          "role": "user",
+          "content": "Hello Gemini!"
+        }
+      ]
+    }
   }
 ]

tests/snapshots/translation/openai-to-gemini/basic-chat.json

@@ -10,7 +10,11 @@
     }
   ],
   "generationConfig": {
-    "maxOutputTokens": 65536
+    "maxOutputTokens": 65536,
+    "thinkingConfig": {
+      "includeThoughts": true,
+      "thinkingBudget": 24576
+    }
   },
   "model": "gemini-2.5-flash",
   "safetySettings": [

tests/snapshots/translation/openai-to-gemini/modern-gemini-default-thinking.json

@@ -0,0 +1,42 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "text": "Hello Gemini!"
+        }
+      ],
+      "role": "user"
+    }
+  ],
+  "generationConfig": {
+    "maxOutputTokens": 65536,
+    "thinkingConfig": {
+      "includeThoughts": true,
+      "thinkingBudget": 24576
+    }
+  },
+  "model": "gemini-2.5-flash",
+  "safetySettings": [
+    {
+      "category": "HARM_CATEGORY_HATE_SPEECH",
+      "threshold": "OFF"
+    },
+    {
+      "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
+      "threshold": "OFF"
+    },
+    {
+      "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
+      "threshold": "OFF"
+    },
+    {
+      "category": "HARM_CATEGORY_HARASSMENT",
+      "threshold": "OFF"
+    },
+    {
+      "category": "HARM_CATEGORY_CIVIC_INTEGRITY",
+      "threshold": "OFF"
+    }
+  ]
+}

tests/snapshots/translation/openai-to-gemini/with-system.json

@@ -11,7 +11,11 @@
   ],
   "generationConfig": {
     "maxOutputTokens": 8192,
-    "temperature": 0.7
+    "temperature": 0.7,
+    "thinkingConfig": {
+      "includeThoughts": true,
+      "thinkingBudget": 24576
+    }
   },
   "model": "gemini-2.5-pro",
   "safetySettings": [