chore: import upstream snapshot with attribution

contributing/samples/core/abort/README.md

@@ -0,0 +1,91 @@
+# Abort Agent Sample
+
+## Overview
+
+This sample demonstrates a standalone ADK agent designed specifically to showcase cooperative task cancellation on client disconnections.
+
+The agent leverages a custom tool that counts from 1 to a target number requested by the user, pausing 1 second between each count and printing the progress directly to the server's stdout terminal. This delay allows you to easily trigger connection drops (by cancelling client requests mid-execution) and visually observe that background agent execution halts immediately in the server terminal, resolving resource leaks.
+
+## Sample Inputs
+
+- `Count to 10 seconds`
+
+  The agent will call the `count_seconds` tool with a target count of 10, pausing 1 second between each increment.
+
+- `Please count up to 20`
+
+  The agent will invoke the tool to count to 20. If you close the client connection (such as pressing `Ctrl+C` in a cURL window or closing your browser tab) while the loop is running, counting halts immediately.
+
+## Graph
+
+```mermaid
+graph TD
+    START --> AbortAgent
+    AbortAgent --> |"Invoke Tool"| count_seconds
+    count_seconds --> |"Abort if Disconnected / Done"| AbortAgent
+    AbortAgent --> ANSWER
+```
+
+## How To
+
+### 1. Running Locally via the CLI
+
+To interact with the agent in your local shell terminal:
+
+```bash
+adk run contributing/samples/core/abort/
+```
+
+Type `count to 10` at the `[user]:` prompt. Pressing `Ctrl+C` mid-run will abort counting and exit.
+
+### 2. Running via HTTP Server and cURL
+
+To verify connection-drop abortion over network protocols (e.g. simple HTTP REST request):
+
+1. Start the local development server to watch the sample workspace:
+   ```bash
+   adk web --allow_origins=http://localhost:4200 contributing/samples/
+   ```
+1. In a separate terminal, register the test session (local CLI development servers run with `--auto_create_session` set to `False` by default):
+   ```bash
+   curl -X POST http://localhost:8000/apps/abort_agent/users/user/sessions \
+     -H "Content-Type: application/json" \
+     -d '{"session_id": "8b24e6ed-1fff-4f0c-a06a-e065692a446e"}'
+   ```
+1. Initiate the count request (this blocks waiting for a response):
+   ```bash
+   curl -X POST http://localhost:8000/run \
+     -H "Content-Type: application/json" \
+     -d '{
+       "app_name": "abort_agent",
+       "user_id": "user",
+       "session_id": "8b24e6ed-1fff-4f0c-a06a-e065692a446e",
+       "new_message": {
+         "role": "user",
+         "parts": [{"text": "count to 100"}]
+       }
+     }'
+   ```
+1. Observe your `adk web` terminal window. You will see the counting progress logging.
+1. **Trigger the Abort**: Press `Ctrl+C` in your cURL terminal window to close the client connection.
+1. Observe the server console window. Counting halts instantly and prints:
+   ```text
+   [Counting Tool] Count was ABORTED mid-run at progress: X/100 (Client Disconnected)!
+   ```
+
+### 3. Running and Testing via ADK Web (Dev UI)
+
+To observe cooperative aborts interactively in the web-based developer interface:
+
+1. Start the local development server:
+   ```bash
+   adk web --allow_origins=http://localhost:4200 contributing/samples/
+   ```
+1. Open the ADK Web interface (`http://localhost:4200`) in your web browser.
+1. Select the **`abort_agent`** app from the left sidebar panel.
+1. Type `count to 100` in the message input box and click submit.
+1. **Trigger the Abort**: Simply close your browser tab, refresh the page, or navigate away from the chat panel.
+1. Observe the server's stdout terminal console. You will see that counting halts immediately and logs:
+   ```text
+   [Counting Tool] Count was ABORTED mid-run (Client Disconnected)!
+   ```