Move thinking block parsing from user to assistant messages (#119)

Related to https://github.com/anthropics/claude-code-sdk-python/pull/28
cc @dicksontsai

src/claude_code_sdk/_internal/message_parser.py

@@ -54,13 +54,6 @@ def parse_message(data: dict[str, Any]) -> Message:
                                 user_content_blocks.append(
                                     TextBlock(text=block["text"])
                                 )
-                            case "thinking":
-                                user_content_blocks.append(
-                                    ThinkingBlock(
-                                        thinking=block["thinking"],
-                                        signature=block["signature"],
-                                    )
-                                )
                             case "tool_use":
                                 user_content_blocks.append(
                                     ToolUseBlock(
@@ -91,6 +84,13 @@ def parse_message(data: dict[str, Any]) -> Message:
                     match block["type"]:
                         case "text":
                             content_blocks.append(TextBlock(text=block["text"]))
+                        case "thinking":
+                            content_blocks.append(
+                                ThinkingBlock(
+                                    thinking=block["thinking"],
+                                    signature=block["signature"],
+                                )
+                            )
                         case "tool_use":
                             content_blocks.append(
                                 ToolUseBlock(

tests/test_message_parser.py

@@ -9,6 +9,7 @@ from claude_code_sdk.types import (
     ResultMessage,
     SystemMessage,
     TextBlock,
+    ThinkingBlock,
     ToolResultBlock,
     ToolUseBlock,
     UserMessage,
@@ -152,6 +153,31 @@ class TestMessageParser:
         assert isinstance(message.content[0], TextBlock)
         assert isinstance(message.content[1], ToolUseBlock)
 
+    def test_parse_assistant_message_with_thinking(self):
+        """Test parsing an assistant message with thinking block."""
+        data = {
+            "type": "assistant",
+            "message": {
+                "content": [
+                    {
+                        "type": "thinking",
+                        "thinking": "I'm thinking about the answer...",
+                        "signature": "sig-123",
+                    },
+                    {"type": "text", "text": "Here's my response"},
+                ],
+                "model": "claude-opus-4-1-20250805",
+            },
+        }
+        message = parse_message(data)
+        assert isinstance(message, AssistantMessage)
+        assert len(message.content) == 2
+        assert isinstance(message.content[0], ThinkingBlock)
+        assert message.content[0].thinking == "I'm thinking about the answer..."
+        assert message.content[0].signature == "sig-123"
+        assert isinstance(message.content[1], TextBlock)
+        assert message.content[1].text == "Here's my response"
+
     def test_parse_valid_system_message(self):
         """Test parsing a valid system message."""
         data = {"type": "system", "subtype": "start"}