chore: import upstream snapshot with attribution

contributing/samples/workflows/message/README.md

@@ -0,0 +1,81 @@
+# ADK Workflow Message Sample
+
+## Overview
+
+This sample demonstrates different ways to send a message to a user using `Event(message=...)` within an **ADK Workflows** node. It covers:
+
+1. **String Messages**: Standard string text replies.
+1. **Multi-modal Messages**: Returning mixed modality inputs, such as a string combined with an inline image.
+1. **Multiple Messages**: Emitting multiple full messages from the same node with a delay between them.
+1. **Streaming Messages**: Simulating an LLM streaming response by breaking a message into chunks and yielding them with the `partial=True` flag at intervals.
+
+## Sample Inputs
+
+This workflow executes sequentially and successfully without any expected user input. Since it has only one `Workflow` node chain that automatically progresses from `START`, you can just type anything (e.g. `start`) to kick it off.
+
+## Graph
+
+```mermaid
+graph TD
+    START --> send_string
+    send_string --> send_multimodal
+    send_multimodal --> multiple_messages
+    multiple_messages --> stream_sentence
+    stream_sentence --> END[Workflow Ends]
+```
+
+## How To
+
+To send messages in an ADK node, yield an `Event` object with the `message` argument:
+
+1. **Send a simple string**:
+
+   ```python
+   yield Event(message="Hello world!")
+   ```
+
+1. **Send text with an image** (multi-modal):
+
+   ```python
+   from google.genai import types
+   yield Event(
+       message=[
+           types.Part.from_text(text="Look at this image:"),
+           types.Part.from_bytes(data=image_bytes, mime_type="image/png"),
+       ]
+   )
+   ```
+
+1. **Send multiple messages**:
+   To send multiple distinct messages from a single node, yield multiple `Event` objects sequentially.
+
+   > **Note**: When yielding multiple messages with delays (`await asyncio.sleep(...)`), your node function **must be an asynchronous generator** (`async def`). This allows ADK to yield each message to the client immediately without blocking.
+
+   ```python
+   import asyncio
+
+   async def multiple_messages(node_input: Any = None):
+     yield Event(message="Processing step 1...")
+     await asyncio.sleep(1.0)
+
+     yield Event(message="Processing step 2...")
+     await asyncio.sleep(1.0)
+
+     yield Event(message="Done processing.")
+   ```
+
+1. **Stream a message in chunks**:
+   Provide the `partial=True` flag for intermediate chunks. This provides a better user experience by allowing the UI to show the response in a streaming fashion, thereby lowering the latency to see the first word. ADK automatically accumulates all partial messages and merges them into a final message for you for session storage.
+
+   > **Note**: To stream multiple messages or tokens smoothly, your node function **must be an asynchronous generator** (`async def`). This allows ADK to yield messages to the client immediately without blocking.
+
+   ```python
+   import asyncio
+
+   async def stream_sentence(node_input: str):
+       yield Event(message="How ", partial=True)
+       await asyncio.sleep(0.5)
+       yield Event(message="may I", partial=True)
+       await asyncio.sleep(0.5)
+       yield Event(message=" help you?", partial=True)
+   ```

contributing/samples/workflows/message/agent.py

@@ -0,0 +1,104 @@
+# 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 asyncio
+import base64
+import os
+from typing import Any
+
+from google.adk import Event
+from google.adk import Workflow
+from google.genai import types
+
+
+async def sleep_if_not_pytest(seconds: float):
+  if "PYTEST_CURRENT_TEST" not in os.environ:
+    await asyncio.sleep(seconds)
+
+
+def send_string(node_input: Any = None):
+  """Sends a single string message."""
+  yield Event(message="#1 This is a simple string message.")
+
+
+def send_multimodal(node_input: Any = None):
+  """Sends a multi-modal message containing a string and an inline image."""
+  # A 16x16 solid red PNG base64 encoded
+  red_square_png = base64.b64decode(
+      "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAAXElEQVR4nO2TSQ7AIAwD"
+      "7fz/z+ZQtapwmrJc8QklmjBIgZJgIZMiAIl9KYbhjx4fgwosbNxgMrF0+4uhgHnYDM6"
+      "AzQHJeg5HYtyHFfgy2AztN/5tZWfrBtVzkl4DzfQkEPd+cEkAAAAASUVORK5CYII="
+  )
+  yield Event(
+      message=[
+          types.Part.from_text(
+              text=(
+                  "#2 Here is a multi-modal message with an inline image (red"
+                  " circle):"
+              )
+          ),
+          types.Part.from_bytes(data=red_square_png, mime_type="image/png"),
+      ]
+  )
+
+
+async def multiple_messages(node_input: Any = None):
+  """Sends multiple complete messages from the same node with an interval."""
+  yield Event(message="#3 Multiple messages")
+  await sleep_if_not_pytest(1.0)
+
+  yield Event(message="Processing step 1...")
+  await sleep_if_not_pytest(1.0)
+
+  yield Event(message="Processing step 2...")
+  await sleep_if_not_pytest(1.0)
+
+  yield Event(message="Done processing.")
+
+
+async def stream_sentence(node_input: Any = None):
+  """
+  Demonstrates streaming by sending a sentence in chunks.
+  The `partial=True` flag tells the UI that this is part of an ongoing message.
+  """
+  yield Event(message="#4 Starting to stream...")
+  sentence = """\
+This is a streaming message sent in chunks.
+
+You can stream in markdown as well. For example, the table below:
+
+| Header 1 | Header 2 |
+|----------|----------|
+| Cell 1   | Cell 2   |
+| Cell 3   | Cell 4   |
+"""
+
+  for i in range(0, len(sentence), 5):
+    chunk = sentence[i : i + 5]
+    yield Event(message=chunk, partial=True)
+    await sleep_if_not_pytest(0.2)
+
+
+root_agent = Workflow(
+    name="message",
+    edges=[
+        (
+            "START",
+            send_string,
+            send_multimodal,
+            multiple_messages,
+            stream_sentence,
+        ),
+    ],
+)

contributing/samples/workflows/message/tests/go.json

@@ -0,0 +1,146 @@
+{
+  "appName": "message",
+  "events": [
+    {
+      "author": "user",
+      "content": {
+        "parts": [
+          {
+            "text": "go"
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-1",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": ""
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "#1 This is a simple string message."
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-2",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/send_string@1"
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "#2 Here is a multi-modal message with an inline image (red circle):"
+          },
+          {
+            "inlineData": {
+              "data": "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8_9hAAAAXElEQVR4nO2TSQ7AIAwD7fz_z-ZQtapwmrJc8QklmjBIgZJgIZMiAIl9KYbhjx4fgwosbNxgMrF0-4uhgHnYDM6AzQHJeg5HYtyHFfgy2AztN_5tZWfrBtVzkl4DzfQkEPd-cEkAAAAASUVORK5CYII=",
+              "mimeType": "image/png"
+            }
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-3",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/send_multimodal@1"
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "#3 Multiple messages"
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-4",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/multiple_messages@1"
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "Processing step 1..."
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-5",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/multiple_messages@1"
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "Processing step 2..."
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-6",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/multiple_messages@1"
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "Done processing."
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-7",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/multiple_messages@1"
+      }
+    },
+    {
+      "author": "message",
+      "content": {
+        "parts": [
+          {
+            "text": "#4 Starting to stream..."
+          }
+        ],
+        "role": "user"
+      },
+      "id": "e-8",
+      "invocationId": "i-1",
+      "nodeInfo": {
+        "path": "message@1/stream_sentence@1"
+      }
+    }
+  ],
+  "id": "9cfc0ef6-11d6-4260-84cf-be22731ab69e",
+  "state": {
+    "__session_metadata__": {
+      "displayName": "go"
+    }
+  },
+  "userId": "user"
+}