Sweeps: Add notes to Sweeps walkthrough and wandb.agent() docs about guarding main when using multiprocessing (#1555)

Description
-----------
Add warnings next to `wandb.agent()` in both the tutorial and
`wandb.agent()` doc about guarding your `wandb.sweep` and `wandb.agent`
calls with `if __name__ == '__main__':` if you're using
`multiprocessing`, along with links to official documentation about it.

`guides/sweeps/walkthrough/`:

<img width="1020" height="516" alt="Screenshot 2025-08-26 at 10 54 07"
src="https://github.com/user-attachments/assets/6285357d-219b-46c7-814d-667445385f73"
/>

`guides/sweeps/start-sweep-agents/`:

<img width="1029" height="1227" alt="Screenshot 2025-08-26 at 10 53 57"
src="https://github.com/user-attachments/assets/e1afac2d-5fe3-4df7-b420-9a5e4ad2c14b"
/>

Related issues
-----------
- Fixes https://wandb.atlassian.net/browse/WB-22363



<!-- preview-links-comment -->

📄 **[View preview links for changed
content](#1555 (comment)

---------

Co-authored-by: Noah Luna <15202580+ngrayluna@users.noreply.github.com>

Author: kelu-wandb

content/en/guides/models/sweeps/start-sweep-agents.md

@@ -41,6 +41,20 @@ Use the W&B Python SDK library to start a sweep. Provide the sweep ID that was r
 ```python
 wandb.agent(sweep_id=sweep_id, function=function_name)
 ```
+
+{{% alert color="secondary" title="Multiprocessing" %}}
+You must wrap your `wandb.agent()` and `wandb.sweep()` calls with `if __name__ == '__main__':` if you use Python standard library's `multiprocessing` or PyTorch's `pytorch.multiprocessing` package. For example:
+
+```python
+if __name__ == '__main__':
+    wandb.agent(sweep_id="<sweep_id>", function="<function>", count="<count>")
+```
+
+Wrapping your code with this convention ensures that it is only executed when the script is run directly, and not when it is imported as a module in a worker process.
+
+See [Python standard library `multiprocessing`](https://docs.python.org/3/library/multiprocessing.html#the-spawn-and-forkserver-start-methods) or [PyTorch `multiprocessing`](https://docs.pytorch.org/docs/stable/notes/multiprocessing.html#asynchronous-multiprocess-training-e-g-hogwild) for more information about multiprocessing. See https://realpython.com/if-name-main-python/ for information about the `if __name__ == '__main__':` convention.
+{{% /alert %}}
+
 {{% /tab %}}
 {{< /tabpane >}}
 
@@ -71,7 +85,7 @@ wandb.agent(sweep_id, count=count)
 
 {{% alert color="secondary" %}}
 If you start a new run after the sweep agent has finished, within the same script or notebook, then you should call `wandb.teardown()` before starting the new run.
-{{% /alert %}}  
+{{% /alert %}}
   {{% /tab %}}
   {{% tab header="CLI" %}}
 First, initialize your sweep with the [`wandb sweep`]({{< relref "/ref/cli/wandb-sweep.md" >}}) command. For more information, see [Initialize sweeps]({{< relref "./initialize-sweeps.md" >}}).
@@ -86,6 +100,6 @@ Pass an integer value to the count flag to set the maximum number of runs to try
 NUM=10
 SWEEPID="dtzl1o7u"
 wandb agent --count $NUM $SWEEPID
-```  
+```
   {{% /tab %}}
 {{< /tabpane >}}

content/en/guides/models/sweeps/walkthrough.md

@@ -19,7 +19,7 @@ This page shows how to define, initialize, and run a sweep. There are four main
 
 Copy and paste the following code into a Jupyter Notebook or Python script:
 
-```python 
+```python
 # Import the W&B Python Library and log into W&B
 import wandb
 
@@ -109,12 +109,26 @@ For more information about initializing sweeps, see [Initialize sweeps]({{< relr
 
 ## Start the Sweep
 
-Use the [`wandb.agent`]({{< relref "/ref/python/sdk/functions/agent.md" >}}) API call to start a sweep.
+Use the [`wandb.agent()`]({{< relref "/ref/python/sdk/functions/agent.md" >}}) API call to start a sweep.
 
 ```python
 wandb.agent(sweep_id, function=main, count=10)
 ```
 
+{{% alert color="secondary" title="Multiprocessing" %}}
+You must wrap your `wandb.agent()` and `wandb.sweep()` calls with `if __name__ == '__main__':` if you use Python standard library's `multiprocessing` or PyTorch's `pytorch.multiprocessing` package. For example:
+
+```python
+if __name__ == '__main__':
+    wandb.agent(sweep_id="<sweep_id>", function="<function>", count="<count>")
+```
+
+Wrapping your code with this convention ensures that it is only executed when the script is run directly, and not when it is imported as a module in a worker process.
+
+See [Python standard library `multiprocessing`](https://docs.python.org/3/library/multiprocessing.html#the-spawn-and-forkserver-start-methods) or [PyTorch `multiprocessing`](https://docs.pytorch.org/docs/stable/notes/multiprocessing.html#asynchronous-multiprocess-training-e-g-hogwild) for more information about multiprocessing. See https://realpython.com/if-name-main-python/ for information about the `if __name__ == '__main__':` convention.
+{{% /alert %}}
+
+
 ## Visualize results (optional)
 
 Open your project to see your live results in the W&B App dashboard. With just a few clicks, construct rich, interactive charts like [parallel coordinates plots]({{< relref "/guides/models/app/features/panels/parallel-coordinates.md" >}}),[ parameter importance analyzes]({{< relref "/guides/models/app/features/panels/parameter-importance.md" >}}), and [additional chart types]({{< relref "/guides/models/app/features/panels/" >}}).
@@ -126,5 +140,3 @@ For more information about how to visualize results, see [Visualize sweep result
 ## Stop the agent (optional)
 
 In the terminal, press `Ctrl+C` to stop the current run. Press it again to terminate the agent.
-
-```