chore: import upstream snapshot with attribution

contributing/samples/workflows/loop_self/README.md

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+# ADK Workflow Loop Self Sample
+
+## Overview
+
+This sample demonstrates how a node can repeatedly loop back to itself based on a specific route condition in **ADK Workflows**.
+
+It takes a user-provided target number (between 0 and 10), and uses a `guess_number` function to randomly generate guesses. If the guess is incorrect, the function yields a specific route (`guessed_wrong`). The workflow is configured such that this route directs the execution right back to the `guess_number` node, creating a loop that continues until the correct number is guessed.
+
+In ADK Workflows, you can create self-referential loops or iterative processes by routing a node's output back to itself.
+
+## Sample Inputs
+
+- `5`
+
+- `0`
+
+- `10`
+
+## Graph
+
+```mermaid
+graph TD
+    START --> validate_input
+    validate_input --> guess_number
+    guess_number -->|guessed_wrong| guess_number
+    guess_number -->|correct| END[Loop ends]
+```
+
+## How To
+
+1. From within your node (agent or function), yield a specific `Event` with a route name when you determine the node needs to be executed again:
+
+   ```python
+   def guess_number(target_number: int):
+     # ...
+     if guess != target_number:
+       yield Event(route='guessed_wrong')
+   ```
+
+1. In the `Workflow` edges definition, create a conditional edge where the source and target are the same node, using a routing map dict:
+
+   ```python
+   (guess_number, {'guessed_wrong': guess_number})
+   ```