chore: Add an a2a sample agent to demo running the a2a server via unvicorn command and run remote agent as root_agent

PiperOrigin-RevId: 785629271

contributing/samples/a2a_root/README.md

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+# A2A Root Sample Agent
+
+This sample demonstrates how to use a **remote Agent-to-Agent (A2A) agent as the root agent** in the Agent Development Kit (ADK). This is a simplified approach where the main agent is actually a remote A2A service, also showcasing how to run remote agents using uvicorn command.
+
+## Overview
+
+The A2A Root sample consists of:
+
+- **Root Agent** (`agent.py`): A remote A2A agent proxy as root agent that talks to a remote a2a agent running on a separate server
+- **Remote Hello World Agent** (`remote_a2a/hello_world/agent.py`): The actual agent implementation that handles dice rolling and prime number checking running on remote server
+
+## Architecture
+
+```
+┌─────────────────┐    ┌────────────────────┐
+│   Root Agent    │───▶│   Remote Hello     │
+│ (RemoteA2aAgent)│    │   World Agent      │
+│ (localhost:8000)│    │  (localhost:8001)  │
+└─────────────────┘    └────────────────────┘
+```
+
+## Key Features
+
+### 1. **Remote A2A as Root Agent**
+- The `root_agent` is a `RemoteA2aAgent` that connects to a remote A2A service
+- Demonstrates how to use remote agents as the primary agent instead of local agents
+- Shows the flexibility of the A2A architecture for distributed agent deployment
+
+### 2. **Uvicorn Server Deployment**
+- The remote agent is served using uvicorn, a lightweight ASGI server
+- Demonstrates a simple way to deploy A2A agents without using the ADK CLI
+- Shows how to expose A2A agents as standalone web services
+
+### 3. **Agent Functionality**
+- **Dice Rolling**: Can roll dice with configurable number of sides
+- **Prime Number Checking**: Can check if numbers are prime
+- **State Management**: Maintains roll history in tool context
+- **Parallel Tool Execution**: Can use multiple tools in parallel
+
+### 4. **Simple Deployment Pattern**
+- Uses the `to_a2a()` utility to convert a standard ADK agent to an A2A service
+- Minimal configuration required for remote agent deployment
+
+## Setup and Usage
+
+### Prerequisites
+
+1. **Start the Remote A2A Agent server**:
+   ```bash
+   # Start the remote agent using uvicorn
+   uvicorn contributing.samples.a2a_root.remote_a2a.hello_world.agent:a2a_app --host localhost --port 8001
+   ```
+
+2. **Run the Main Agent**:
+   ```bash
+   # In a separate terminal, run the adk web server
+   adk web contributing/samples/
+   ```
+
+### Example Interactions
+
+Once both services are running, you can interact with the root agent:
+
+**Simple Dice Rolling:**
+```
+User: Roll a 6-sided die
+Bot: I rolled a 4 for you.
+```
+
+**Prime Number Checking:**
+```
+User: Is 7 a prime number?
+Bot: Yes, 7 is a prime number.
+```
+
+**Combined Operations:**
+```
+User: Roll a 10-sided die and check if it's prime
+Bot: I rolled an 8 for you.
+Bot: 8 is not a prime number.
+```
+
+**Multiple Rolls with Prime Checking:**
+```
+User: Roll a die 3 times and check which results are prime
+Bot: I rolled a 3 for you.
+Bot: I rolled a 7 for you.
+Bot: I rolled a 4 for you.
+Bot: 3, 7 are prime numbers.
+```
+
+## Code Structure
+
+### Root Agent (`agent.py`)
+
+- **`root_agent`**: A `RemoteA2aAgent` that connects to the remote A2A service
+- **Agent Card URL**: Points to the well-known agent card endpoint on the remote server
+
+### Remote Hello World Agent (`remote_a2a/hello_world/agent.py`)
+
+- **`roll_die(sides: int)`**: Function tool for rolling dice with state management
+- **`check_prime(nums: list[int])`**: Async function for prime number checking
+- **`root_agent`**: The main agent with comprehensive instructions
+- **`a2a_app`**: The A2A application created using `to_a2a()` utility
+
+
+
+## Troubleshooting
+
+**Connection Issues:**
+- Ensure the uvicorn server is running on port 8001
+- Check that no firewall is blocking localhost connections
+- Verify the agent card URL in the root agent configuration
+- Check uvicorn logs for any startup errors
+
+**Agent Not Responding:**
+- Check the uvicorn server logs for errors
+- Verify the agent instructions are clear and unambiguous
+- Ensure the A2A app is properly configured with the correct port
+
+**Uvicorn Issues:**
+- Make sure the module path is correct: `contributing.samples.a2a_root.remote_a2a.hello_world.agent:a2a_app`
+- Check that all dependencies are installed

contributing/samples/a2a_root/agent.py

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+# Copyright 2025 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 a2a.utils.constants import AGENT_CARD_WELL_KNOWN_PATH
+from google.adk.agents.remote_a2a_agent import RemoteA2aAgent
+
+root_agent = RemoteA2aAgent(
+    name="hello_world_agent",
+    description=(
+        "Helpful assistant that can roll dice and check if numbers are prime."
+    ),
+    agent_card=f"http://localhost:8001/{AGENT_CARD_WELL_KNOWN_PATH}",
+)

contributing/samples/a2a_root/remote_a2a/hello_world/__init__.py

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+# Copyright 2025 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/a2a_root/remote_a2a/hello_world/agent.py

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+# Copyright 2025 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 random
+
+from google.adk import Agent
+from google.adk.a2a.utils.agent_to_a2a import to_a2a
+from google.adk.tools.tool_context import ToolContext
+from google.genai import types
+
+
+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.
+    tool_context: the tool context
+  Returns:
+    An integer of the result of rolling the die.
+  """
+  result = random.randint(1, sides)
+  if not 'rolls' in tool_context.state:
+    tool_context.state['rolls'] = []
+
+  tool_context.state['rolls'] = tool_context.state['rolls'] + [result]
+  return result
+
+
+async def check_prime(nums: list[int]) -> str:
+  """Check if a given list of numbers are prime.
+
+  Args:
+    nums: The list of numbers to check.
+
+  Returns:
+    A str indicating which number is prime.
+  """
+  primes = set()
+  for number in nums:
+    number = int(number)
+    if number <= 1:
+      continue
+    is_prime = True
+    for i in range(2, int(number**0.5) + 1):
+      if number % i == 0:
+        is_prime = False
+        break
+    if is_prime:
+      primes.add(number)
+  return (
+      'No prime numbers found.'
+      if not primes
+      else f"{', '.join(str(num) for num in primes)} are prime numbers."
+  )
+
+
+root_agent = Agent(
+    model='gemini-2.0-flash',
+    name='hello_world_agent',
+    description=(
+        'hello world agent that can roll a dice of 8 sides and check prime'
+        ' numbers.'
+    ),
+    instruction="""
+      You roll dice and answer questions about the outcome of the dice rolls.
+      You can roll dice of different sizes.
+      You can use multiple tools in parallel by calling functions in parallel(in one request and in one round).
+      It is ok to discuss previous dice roles, and comment on the dice rolls.
+      When you are asked to roll a die, you must call the roll_die tool with the number of sides. Be sure to pass in an integer. Do not pass in a string.
+      You should never roll a die on your own.
+      When checking prime numbers, call the check_prime tool with a list of integers. Be sure to pass in a list of integers. You should never pass in a string.
+      You should not check prime numbers before calling the tool.
+      When you are asked to roll a die and check prime numbers, you should always make the following two function calls:
+      1. You should first call the roll_die tool to get a roll. Wait for the function response before calling the check_prime tool.
+      2. After you get the function response from roll_die tool, you should call the check_prime tool with the roll_die result.
+        2.1 If user asks you to check primes based on previous rolls, make sure you include the previous rolls in the list.
+      3. When you respond, you must include the roll_die result from step 1.
+      You should always perform the previous 3 steps when asking for a roll and checking prime numbers.
+      You should not rely on the previous history on prime results.
+    """,
+    tools=[
+        roll_die,
+        check_prime,
+    ],
+    # planner=BuiltInPlanner(
+    #     thinking_config=types.ThinkingConfig(
+    #         include_thoughts=True,
+    #     ),
+    # ),
+    generate_content_config=types.GenerateContentConfig(
+        safety_settings=[
+            types.SafetySetting(  # avoid false alarm about rolling dice.
+                category=types.HarmCategory.HARM_CATEGORY_DANGEROUS_CONTENT,
+                threshold=types.HarmBlockThreshold.OFF,
+            ),
+        ]
+    ),
+)
+
+a2a_app = to_a2a(root_agent, port=8001)