Support Anthropic's native tool calling API

pkg/api/api.go

@@ -40,3 +40,10 @@ type ChatCompletionProvider interface {
 		chunks chan<- Chunk,
 	) (*Message, error)
 }
+
+func IsAssistantContinuation(messages []Message) bool {
+	if len(messages) == 0 {
+		return false
+	}
+	return messages[len(messages)-1].Role == MessageRoleAssistant
+}