- Grepped for callsites.
- Ran `arc patch --trace` in a Git working copy and saw the updated "git apply" in the trace output.
- Used this test script to confirm that success and error behavior is identical in "resolve()" and "execute()", except that "execute()" now emits a deprecation warning:
```
<?php
require_once 'support/init/init-script.php';
$err = id(new PhutilExecPassthru('lsx'))->execute();
var_dump($err);
```