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/agents/hopper/hopper.py

@@ -0,0 +1,93 @@
+# 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 pathlib import Path
+
+from jinja2 import Template
+from langchain_core.messages import HumanMessage, SystemMessage
+from artemis.context import ArtemisContext
+from artemis.data_engine.trace import trace
+from artemis.services.llm import get_llm, invoke_llm_with_timeout_message, with_fallback
+from artemis.utils.logger import get_logger
+from pydantic import BaseModel, Field
+
+logger = get_logger(__name__)
+
+
+class _CyFunctionDetectorMeta(type):
+    def __instancecheck__(self, instance):
+        name = type(instance).__name__
+        return (
+            name
+            in (
+                "cyfunction",
+                "cython_function_or_method",
+                "builtin_function_or_method",
+            )
+            or "cyfunction" in name.lower()
+        )
+
+
+class CyFunctionDetector(metaclass=_CyFunctionDetectorMeta):
+    pass
+
+
+class HopperOutput(BaseModel):
+    model_config = {"ignored_types": (CyFunctionDetector,)}
+    found: bool = Field(description="True if the requested data was found, False otherwise.")
+    output: str | None = Field(description="The extracted data if found, null otherwise.")
+    reason: str = Field(
+        description="A short explanation of what you looked for"
+        + " and how you decided what to extract."
+    )
+
+
+@trace(type="agent", name="hopper")
+async def hopper(
+    ctx: ArtemisContext,
+    request: str,
+    data: str,
+    use_fallback: bool = True,
+) -> HopperOutput:
+    logger.info(f"Starting Hopper Agent (use_fallback={use_fallback})")
+    system_message = Template(
+        Path(__file__).parent.joinpath("hopper.md").read_text(encoding="utf-8")
+    ).render()
+    messages = [
+        SystemMessage(content=system_message),
+        HumanMessage(content=f"{request}\nHere is the data you must dig:\n{data}"),
+    ]
+
+    llm = get_llm(ctx=ctx, name="hopper", is_utils=True).with_structured_output(HopperOutput)
+    try:
+        if use_fallback:
+            llm_fallback = get_llm(
+                ctx=ctx, name="hopper", is_utils=True, use_fallback=True
+            ).with_structured_output(HopperOutput)
+            response: HopperOutput = await with_fallback(
+                main_call=lambda: invoke_llm_with_timeout_message(llm.ainvoke(messages)),
+                fallback_call=lambda: invoke_llm_with_timeout_message(
+                    llm_fallback.ainvoke(messages)
+                ),
+            )  # type: ignore
+        else:
+            response: HopperOutput = await invoke_llm_with_timeout_message(llm.ainvoke(messages))
+        return response
+    except Exception as e:
+        logger.error(f"Hopper LLM invocation failed: {e}")
+        return HopperOutput(
+            found=False,
+            output=None,
+            reason=f"Failed due to LLM error: {str(e)[:500]}",
+        )