In v0.3.0, ExecuteAbilityAbility returns error messages in a format that ToolsHandler cannot parse, causing all error messages from ExecuteAbilityAbility to be replaced with the generic fallback: "An error occurred while executing the tool."

It seems that ExecuteAbilityAbility.php returns errors as:

 array(
      'success' => false,
      'error'   => 'Error message string'
  )

But ToolsHandler.php expects errors in this format:

  array(
      'error' => array(
          'message' => 'Error message'
      )
  )

As seen here in the default fallback message triggering here:

$error_message = $result['error']['message'] ?? 'An error occurred while executing the tool.';

Steps to reproduce

1. Call any ability that returns an error, like an outpu validation error
2. See that instead of the actual error message, you get the generic message