## Motivation for the change, related issues

The [new Comlink error
handler](#2357)
rewired the logic around passing errors from web workers to the
Playground web app. Specifically, it enriched the error with additional
stack trace before rethrowing it:

```js
throw new Error('Comlink method call failed', {
	cause: originalError
});
```

Unfortunately, this also put the original error at the bottom of the
`error.cause` chain, making error handling confusing for the API
consumers.

This PR ensures the thrown error the original one. This way a simple
`try {} catch(e) {}` is enough to log the error details without having
to reason about `e.cause.cause` etc. The additional stack trace
information is now attached at the bottom of the cause chain for when
the developer needs to inspect it.

## Testing Instructions (or ideally a Blueprint)

Run Playground with this Blueprint and confirm the top-level error
message speaks about PHP failure. Specifically, it should not say
"Comlink method call failed":

```json
{
  "steps": [
    {
      "step": "mkdir",
      "path": "/wordpress/wp-content/mu-plugins"
    },
    {
      "step": "writeFile",
      "path": "/wordpress/wp-content/mu-plugins/test.php",
      "data": "<?php undefined_function();"
    }
  ]
}
```

…rors (#2429)

## Motivation for the change, related issues

The [recent
PR](#2357), that
altered how error reporting works, unintentionally removed the
`request.error` event in some PHP.run() code paths. This PR makes sure
the `request.error` event is emitted anytime a non-zero-exit error
happens.

## Testing Instructions (or ideally a Blueprint)

CI tests