Improve message format and support translation

includes/run.php

@@ -11,12 +11,12 @@ namespace Automattic\WP\WP_CLI_Cron_Control_Offload;
 function run_event( $command ) {
 	if ( ! defined( 'WP_CLI' ) || ! \WP_CLI ) {
 		// TODO: reschedule at least once or twice
-		trigger_error( 'Attempted to run event without WP-CLI loaded. (' . var_export( $command, true ) . ')', E_USER_WARNING );
+		trigger_error( sprintf( __( '%1$s: Attempted to run event without WP-CLI loaded. (%2$s)', 'wp-cli-cron-control-offload' ), MESSAGE_PREFIX, var_export( $command, true ) ), E_USER_WARNING );
 		return;
 	}
 
 	if ( ! validate_args( $command ) ) {
-		trigger_error( 'Attempted to run blocked WP-CLI command. (' . var_export( $command, true ) . ')', E_USER_WARNING );
+		trigger_error( sprintf( __( '%1$s: Attempted to run blocked WP-CLI command. (%2$s)', 'wp-cli-cron-control-offload' ), MESSAGE_PREFIX, var_export( $command, true ) ), E_USER_WARNING );
 		return;
 	}
 
@@ -32,9 +32,10 @@ function run_event( $command ) {
 
 	// Command failed
 	if ( ! is_object( $output ) || is_wp_error( $output ) ) {
-		// TODO: message consistency, revisit using ACTION as the "key", seems wrong
-		trigger_error( 'WP-CLI command failed. (' . var_export( $command, true ) . ')', E_USER_WARNING );
-		trigger_error( var_export( $output, true ), E_USER_WARNING );
+		trigger_error( sprintf( __( '%1$s: WP-CLI command failed. (%2$s)', 'wp-cli-cron-control-offload' ), MESSAGE_PREFIX, var_export( $command, true ) ), E_USER_WARNING );
+
+		$message = is_wp_error( $output ) ? $output->get_error_message() : var_export( $output, true );
+		trigger_error( $message, E_USER_WARNING );
 		return;
 	}
 
@@ -45,7 +46,7 @@ function run_event( $command ) {
 	$output->duration = $end - $start;
 
 	$output = var_export( $output, true );
-	$output = ACTION . ":\n{$output}";
+	$output = MESSAGE_PREFIX . ":\n{$output}";
 
 	error_log( $output );
 }

wp-cli-cron-control-offload.php

@@ -14,7 +14,8 @@
 
 namespace Automattic\WP\WP_CLI_Cron_Control_Offload;
 
-const ACTION = 'wp_cli_cron_control_offload';
+const ACTION         = 'wp_cli_cron_control_offload';
+const MESSAGE_PREFIX = 'WP-CLI via Cron';
 
 require_once __DIR__ . '/includes/functions.php';
 require_once __DIR__ . '/includes/schedule.php';