chore: import upstream snapshot with attribution

contributing/samples/core/empty_agent/README.md

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+# ADK Agent Empty Sample
+
+## Overview
+
+This sample demonstrates how to create a minimal, empty agent using the **ADK** framework.
+
+It defines a simple `Agent` that doesn't have any specific tools or complex instructions attached to it. This is useful as a basic template or starting point for defining more complex agentic behaviors over time, ensuring it follows the core directory requirements of `adk`.
+
+## Sample Inputs
+
+- `go`
+
+## Graph
+
+```mermaid
+graph TD
+    empty_agent[Agent: empty_agent]
+```
+
+## How To
+
+1. Define a basic agent using the `Agent` class, specifying a unique name:
+
+   ```python
+   from google.adk.agents import Agent
+
+   root_agent = Agent(
+       name="empty_agent",
+   )
+   ```

contributing/samples/core/empty_agent/__init__.py

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+# 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 __future__ import annotations
+
+from . import agent

contributing/samples/core/empty_agent/agent.py

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+# 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 __future__ import annotations
+
+from google.adk.agents import Agent
+
+root_agent = Agent(
+    name="empty_agent",
+)

contributing/samples/core/empty_agent/tests/go.json

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+{
+  "events": [
+    {
+      "author": "user",
+      "content": {
+        "parts": [
+          {
+            "text": "go"
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-1",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": ""
+      }
+    },
+    {
+      "author": "empty_agent",
+      "content": {
+        "parts": [
+          {
+            "text": "Okay, I'm ready! What would you like to do or talk about?"
+          }
+        ],
+        "role": "model"
+      },
+      "finishReason": "STOP",
+      "id": "e-2",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "empty_agent@1"
+      }
+    }
+  ]
+}

contributing/samples/core/empty_agent/tests/hello.json

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+{
+  "events": [
+    {
+      "author": "user",
+      "content": {
+        "parts": [
+          {
+            "text": "Hello"
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-1",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": ""
+      }
+    },
+    {
+      "author": "empty_agent",
+      "content": {
+        "parts": [
+          {
+            "text": "Hello there! How can I help you today?"
+          }
+        ],
+        "role": "model"
+      },
+      "finishReason": "STOP",
+      "id": "e-2",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "empty_agent@1"
+      }
+    }
+  ]
+}

contributing/samples/core/empty_agent/tests/how_are_you.json

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+{
+  "events": [
+    {
+      "author": "user",
+      "content": {
+        "parts": [
+          {
+            "text": "How are you?"
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-1",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": ""
+      }
+    },
+    {
+      "author": "empty_agent",
+      "content": {
+        "parts": [
+          {
+            "text": "As an AI, I don't have feelings or a physical state, so I can't be \"fine\" in the human sense. However, I'm ready and operational to help you!\n\nHow can I assist you today?"
+          }
+        ],
+        "role": "model"
+      },
+      "finishReason": "STOP",
+      "id": "e-2",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "empty_agent@1"
+      }
+    }
+  ]
+}