Add comments + fix action_yaml schema

src/Runner.Worker/Handlers/CompositeActionHandler.cs

@@ -17,5 +17,58 @@ namespace GitHub.Runner.Worker.Handlers
     }
 
     // TODO: IMPLEMENT LOGIC FOR HANDLER CODE
-    
+    public sealed class CompositeActionHandler : Handler, ICompositeActionHandler
+    {
+        public CompositeActionExecutionData Data { get; set; }
+
+        public async Task RunAsync(ActionRunStage stage) 
+        {
+            // Copied from NodEscriptActionHandler.cs
+            // Validate args.
+            Trace.Entering();
+            ArgUtil.NotNull(Data, nameof(Data));
+            ArgUtil.NotNull(ExecutionContext, nameof(ExecutionContext));
+            ArgUtil.NotNull(Inputs, nameof(Inputs));
+            ArgUtil.Directory(ActionDirectory, nameof(ActionDirectory));
+
+            // Update the env dictionary.
+            AddInputsToEnvironment();
+            AddPrependPathToEnvironment();
+
+            // expose context to environment
+            // for example, this is how we know what OS the runner is running on
+            foreach (var context in ExecutionContext.ExpressionValues)
+            {
+                if (context.Value is IEnvironmentContextData runtimeContext && runtimeContext != null)
+                {
+                    foreach (var env in runtimeContext.GetRuntimeEnvironmentVariables())
+                    {
+                        Environment[env.Key] = env.Value;
+                    }
+                }
+            }
+
+            // Add Actions Runtime server info
+            var systemConnection = ExecutionContext.Endpoints.Single(x => string.Equals(x.Name, WellKnownServiceEndpointNames.SystemVssConnection, StringComparison.OrdinalIgnoreCase));
+            Environment["ACTIONS_RUNTIME_URL"] = systemConnection.Url.AbsoluteUri;
+            Environment["ACTIONS_RUNTIME_TOKEN"] = systemConnection.Authorization.Parameters[EndpointAuthorizationParameters.AccessToken];
+            if (systemConnection.Data.TryGetValue("CacheServerUrl", out var cacheUrl) && !string.IsNullOrEmpty(cacheUrl))
+            {
+                Environment["ACTIONS_CACHE_URL"] = cacheUrl;
+            }
+
+            // Resolve steps
+            // How do I handle the MappingToken?
+            MappingToken target = null;
+            if (stage == ActionRunStage.Main)
+            {
+                target = Data.Steps;
+            }
+
+
+
+
+
+        }
+    }
 }