Composite Action Step Markers (#4243)

src/Runner.Common/ActionCommand.cs

@@ -204,6 +204,26 @@ namespace GitHub.Runner.Common
             return unescaped;
         }
 
+        /// <summary>
+        /// Escapes special characters in a value using the standard action command escape mappings.
+        /// Iterates in reverse so that '%' is escaped first to avoid double-encoding.
+        /// </summary>
+        public static string EscapeValue(string value)
+        {
+            if (string.IsNullOrEmpty(value))
+            {
+                return value;
+            }
+
+            string escaped = value;
+            for (int i = _escapeMappings.Length - 1; i >= 0; i--)
+            {
+                escaped = escaped.Replace(_escapeMappings[i].Token, _escapeMappings[i].Replacement);
+            }
+
+            return escaped;
+        }
+
         private static string UnescapeProperty(string escaped)
         {
             if (string.IsNullOrEmpty(escaped))

src/Runner.Common/Constants.cs

@@ -174,6 +174,7 @@ namespace GitHub.Runner.Common
                 public static readonly string CompareWorkflowParser = "actions_runner_compare_workflow_parser";
                 public static readonly string SetOrchestrationIdEnvForActions = "actions_set_orchestration_id_env_for_actions";
                 public static readonly string SendJobLevelAnnotations = "actions_send_job_level_annotations";
+                public static readonly string EmitCompositeMarkers = "actions_runner_emit_composite_markers";
             }
 
             // Node version migration related constants
@@ -288,6 +289,7 @@ namespace GitHub.Runner.Common
                 public static readonly string ForcedActionsNodeVersion = "ACTIONS_RUNNER_FORCE_ACTIONS_NODE_VERSION";
                 public static readonly string PrintLogToStdout = "ACTIONS_RUNNER_PRINT_LOG_TO_STDOUT";
                 public static readonly string ActionArchiveCacheDirectory = "ACTIONS_RUNNER_ACTION_ARCHIVE_CACHE";
+                public static readonly string EmitCompositeMarkers = "ACTIONS_RUNNER_EMIT_COMPOSITE_MARKERS";
             }
 
             public static class System