Revert "refactor: clean up legacy code, rename hopper to entity_extractor, and add third-party notices"

This reverts commit 54fcef9887.

Please do not submit unrelated docs and codes in the same commit. I am reverting this commit so that the related files can be submitted in better-organized future commits.

artemis/utils/conversations.py

@@ -0,0 +1,45 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import TypeGuard
+
+from langchain_core.messages import AIMessage, BaseMessage, HumanMessage, ToolMessage
+
+
+def is_ai_message(message: BaseMessage) -> TypeGuard[AIMessage]:
+    return isinstance(message, AIMessage)
+
+
+def is_human_message(message: BaseMessage) -> TypeGuard[HumanMessage]:
+    return isinstance(message, HumanMessage)
+
+
+def is_tool_message(message: BaseMessage) -> TypeGuard[ToolMessage]:
+    return isinstance(message, ToolMessage)
+
+
+def is_tool_for_name(tool_message: ToolMessage, name: str) -> bool:
+    return tool_message.name == name
+
+
+def get_screenshot_message_for_llm(screenshot_base64: str):
+    prefix = "" if screenshot_base64.startswith("data:image") else "data:image/jpeg;base64,"
+    return HumanMessage(
+        content=[
+            {
+                "type": "image_url",
+                "image_url": {"url": f"{prefix}{screenshot_base64}"},
+            }
+        ]
+    )