chore: import upstream snapshot with attribution

contributing/samples/tools/built_in_multi_tools/README.md

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+This agent is to demonstrate that the built-in google search tool and the
+VertexAiSearchTool can be used together with other tools, even though the model
+has the limitation that built-in tool cannot be used by other tools.
+
+It is achieved by the workarounds added in https://github.com/google/adk-python/blob/4485379a049a5c84583a43c85d444ea1f1ba6f12/src/google/adk/agents/llm_agent.py#L124-L149.
+
+To run this agent, set the environment variable `VERTEXAI_DATASTORE_ID`
+(e.g.
+`projects/{project}/locations/{location}/collections/{collection}/dataStores/{dataStore}`)
+and use `adk web`.
+
+You can follow
+https://cloud.google.com/generative-ai-app-builder/docs/create-data-store-es
+to set up the datastore.

contributing/samples/tools/built_in_multi_tools/__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 . import agent

contributing/samples/tools/built_in_multi_tools/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.
+
+import os
+import random
+
+from dotenv import load_dotenv
+from google.adk import Agent
+from google.adk.tools.google_search_tool import GoogleSearchTool
+from google.adk.tools.tool_context import ToolContext
+from google.adk.tools.vertex_ai_search_tool import VertexAiSearchTool
+
+load_dotenv(override=True)
+
+VERTEXAI_DATASTORE_ID = os.getenv("VERTEXAI_DATASTORE_ID")
+if not VERTEXAI_DATASTORE_ID:
+  raise ValueError("VERTEXAI_DATASTORE_ID environment variable not set")
+
+
+def roll_die(sides: int, tool_context: ToolContext) -> int:
+  """Roll a die and return the rolled result.
+
+  Args:
+    sides: The integer number of sides the die has.
+
+  Returns:
+    An integer of the result of rolling the die.
+  """
+  result = random.randint(1, sides)
+  if "rolls" not in tool_context.state:
+    tool_context.state["rolls"] = []
+
+  tool_context.state["rolls"] = tool_context.state["rolls"] + [result]
+  return result
+
+
+root_agent = Agent(
+    model="gemini-2.5-pro",
+    name="hello_world_agent",
+    description="A hello world agent with multiple tools.",
+    instruction="""
+      You are a helpful assistant which can help user to roll dice and search for information.
+      - Use `roll_die` tool to roll dice.
+      - Use `VertexAISearchTool` to search for Google Agent Development Kit (ADK) information in the datastore.
+      - Use `google_search` to search for general information.
+    """,
+    tools=[
+        roll_die,
+        VertexAiSearchTool(
+            data_store_id=VERTEXAI_DATASTORE_ID, bypass_multi_tools_limit=True
+        ),
+        GoogleSearchTool(bypass_multi_tools_limit=True),
+    ],
+)