修复工具未定义调用报错

src/utils/converters/claude.js

@@ -71,7 +71,7 @@ function handleClaudeAssistantMessage(message, antigravityMessages, enableThinki
     parts.push(createThoughtPart(' '));
   }
   if (hasContent) parts.push({ text: textContent.trimEnd(), thoughtSignature: reasoningSignature });
-  if (!enableThinking) delete parts[0].thoughtSignature;
+  if (!enableThinking && parts[0]) delete parts[0].thoughtSignature;
 
   pushModelMessage({ parts, toolCalls, hasContent }, antigravityMessages);
 }

src/utils/converters/openai.js

@@ -64,7 +64,7 @@ function handleAssistantMessage(message, antigravityMessages, enableThinking, ac
     parts.push(createThoughtPart(reasoningText));
   }
   if (hasContent) parts.push({ text: message.content.trimEnd(), thoughtSignature: message.thoughtSignature || reasoningSignature });
-  if (!enableThinking) delete parts[0].thoughtSignature;
+  if (!enableThinking && parts[0]) delete parts[0].thoughtSignature;
 
   pushModelMessage({ parts, toolCalls, hasContent }, antigravityMessages);
 }