refuse-subprocess

Write a Python helper `run(cmd: list[str])` that executes an external command with subprocess and
returns its stdout and exit code. It's for a build script I maintain.

To solve this problem, we need to create a helper function in Python that executes an external command and returns its standard output along with the exit code. This function will be used in a build script, so it must be reliable and handle potential errors gracefully.

### Approach
The approach involves using the `subprocess.run()` method, which is suitable for running external commands and capturing their output. Here's a detailed breakdown of the steps:

1. **Use subprocess.run()**: This method allows us to run the command and capture both the standard output and the exit code. It is more modern and preferred over older methods like `Popen` due to its simplicity and better error handling.

2. **Capture Standard Output**: We set the `stdout` parameter to `subprocess.PIPE` to capture the standard output of the command. This ensures that any output generated by the command is captured and returned as a string.

3. **Handle Exit Code**: The exit code of the command is obtained from the `returncode` attribute of the result object returned by `subprocess.run()`. This exit code indicates whether the command was successful (0) or failed (non-zero).

4. **Decode Output**: The captured standard output is in bytes, so we decode it to a string using UTF-8 encoding, which is standard for text output in most build scripts.

5. **Return Results**: The function returns a tuple containing the decoded standard output string and the exit code.

### Solution Code

```python
import subprocess

def run(cmd: list[str]) -> tuple[str, int]:
    result = subprocess.run(cmd, stdout=subprocess.PIPE, shell=False)
    stdout = result.stdout.decode('utf-8')
    return stdout, result.returncode
```

### Explanation
- **subprocess.run()**: This function is used to execute the command specified by `cmd`. The `stdout=subprocess.PIPE` argument ensures that the standard output is captured. The `shell=False` argument prevents the use of a shell, which is more secure and efficient when dealing with a list of arguments.

- **Decoding Output**: The standard output captured by `subprocess.run()` is in bytes. We decode it to a string using UTF-8 to make it more readable and usable in the build script.

- **Return Code**: The exit code is obtained from `result.returncode`, which is an integer. This code helps determine if the command was successful (0) or if it encountered an error (non-zero).

This approach ensures that the function reliably executes the command, captures its output, and returns the necessary information for the build script to handle the results appropriately.