Fix uncaught TypeError on string or non-dict message content

src/claude_agent_sdk/_internal/message_parser.py

@@ -86,6 +86,12 @@ def parse_message(data: dict[str, Any]) -> Message | None:
                 if isinstance(data["message"]["content"], list):
                     user_content_blocks: list[ContentBlock] = []
                     for block in data["message"]["content"]:
+                        if not isinstance(block, dict):
+                            raise MessageParseError(
+                                f"Invalid content block (expected dict, got "
+                                f"{type(block).__name__})",
+                                data,
+                            )
                         match block["type"]:
                             case "text":
                                 user_content_blocks.append(
@@ -126,8 +132,21 @@ def parse_message(data: dict[str, Any]) -> Message | None:
 
         case "assistant":
             try:
+                raw_content = data["message"]["content"]
+                if not isinstance(raw_content, list):
+                    raise MessageParseError(
+                        f"Invalid assistant content (expected list, got "
+                        f"{type(raw_content).__name__})",
+                        data,
+                    )
                 content_blocks: list[ContentBlock] = []
-                for block in data["message"]["content"]:
+                for block in raw_content:
+                    if not isinstance(block, dict):
+                        raise MessageParseError(
+                            f"Invalid content block (expected dict, got "
+                            f"{type(block).__name__})",
+                            data,
+                        )
                     match block["type"]:
                         case "text":
                             content_blocks.append(TextBlock(text=block["text"]))

tests/test_message_parser.py

@@ -886,6 +886,22 @@ def test_parse_assistant_message_missing_fields(self):
             parse_message({"type": "assistant"})
         assert "Missing required field in assistant message" in str(exc_info.value)
 
+    def test_parse_assistant_string_content_raises(self):
+        """Assistant content as a bare string raises MessageParseError, not a raw TypeError."""
+        with pytest.raises(MessageParseError):
+            parse_message(
+                {"type": "assistant", "message": {"model": "m", "content": "hi"}}
+            )
+
+    @pytest.mark.parametrize("role", ["assistant", "user"])
+    def test_non_dict_content_block_raises_documented_error(self, role: str) -> None:
+        """A non-dict block raises MessageParseError, never a raw TypeError."""
+        message: dict[str, object] = {"content": ["oops"]}
+        if role == "assistant":
+            message["model"] = "m"
+        with pytest.raises(MessageParseError):
+            parse_message({"type": role, "message": message})
+
     def test_parse_system_message_missing_fields(self):
         """Test that system message with missing fields raises MessageParseError."""
         with pytest.raises(MessageParseError) as exc_info: