Allow waiting for starting complete

Did this by creating an output for starting

internal/step/plugin/provider.go

@@ -321,6 +321,21 @@ func (r *runnableStep) RunSchema() map[string]*schema.PropertySchema {
 	}
 }
 
+type StartedOutput struct{}
+
+func (r *runnableStep) StartedSchema() *schema.StepOutputSchema {
+	return schema.NewStepOutputSchema(
+		schema.NewScopeSchema(
+			schema.NewObjectSchema(
+				"StartedOutput",
+				map[string]*schema.PropertySchema{},
+			),
+		),
+		nil,
+		false,
+	)
+}
+
 func (r *runnableStep) Lifecycle(input map[string]any) (result step.Lifecycle[step.LifecycleStageWithSchema], err error) {
 	rawStepID, ok := input["step"]
 	if !ok || rawStepID == nil {
@@ -447,6 +462,9 @@ func (r *runnableStep) Lifecycle(input map[string]any) (result step.Lifecycle[st
 						nil,
 					),
 				},
+				Outputs: map[string]*schema.StepOutputSchema{
+					"started": r.StartedSchema(),
+				},
 			},
 			{
 				LifecycleStage: runningLifecycleStage,
@@ -954,7 +972,8 @@ func (r *runningStep) startStage(container deployer.Plugin) error {
 
 func (r *runningStep) runStage() error {
 	r.logger.Debugf("Running stage for step %s/%s", r.runID, r.pluginStepID)
-	r.transitionStage(StageIDRunning, step.RunningStepStateRunning)
+	startedOutput := any(map[any]any{})
+	r.transitionStageWithOutput(StageIDRunning, step.RunningStepStateRunning, schema.PointerTo("started"), &startedOutput)
 
 	var result atp.ExecutionResult
 	select {
@@ -981,7 +1000,7 @@ func (r *runningStep) runStage() error {
 
 	// Execution complete, move to state running stage outputs, then to state finished stage.
 	r.transitionStage(StageIDOutput, step.RunningStepStateRunning)
-	r.completeStage(r.currentStage, step.RunningStepStateFinished, &result.OutputID, &result.OutputData)
+	r.completeStep(r.currentStage, step.RunningStepStateFinished, &result.OutputID, &result.OutputData)
 
 	return nil
 }
@@ -996,7 +1015,7 @@ func (r *runningStep) deployFailed(err error) {
 	output := any(DeployFailed{
 		Error: err.Error(),
 	})
-	r.completeStage(StageIDDeployFailed, step.RunningStepStateFinished, &outputID, &output)
+	r.completeStep(StageIDDeployFailed, step.RunningStepStateFinished, &outputID, &output)
 }
 
 func (r *runningStep) startFailed(err error) {
@@ -1010,7 +1029,7 @@ func (r *runningStep) startFailed(err error) {
 		Output: err.Error(),
 	})
 
-	r.completeStage(StageIDCrashed, step.RunningStepStateFinished, &outputID, &output)
+	r.completeStep(StageIDCrashed, step.RunningStepStateFinished, &outputID, &output)
 }
 
 func (r *runningStep) runFailed(err error) {
@@ -1023,13 +1042,20 @@ func (r *runningStep) runFailed(err error) {
 	output := any(Crashed{
 		Output: err.Error(),
 	})
-	r.completeStage(StageIDCrashed, step.RunningStepStateFinished, &outputID, &output)
+	r.completeStep(StageIDCrashed, step.RunningStepStateFinished, &outputID, &output)
 }
 
 // TransitionStage transitions the stage to the specified stage, and the state to the specified state.
 //
 //nolint:unparam
 func (r *runningStep) transitionStage(newStage StageID, state step.RunningStepState) {
+	r.transitionStageWithOutput(newStage, state, nil, nil)
+}
+
+// TransitionStage transitions the stage to the specified stage, and the state to the specified state.
+//
+//nolint:unparam
+func (r *runningStep) transitionStageWithOutput(newStage StageID, state step.RunningStepState, outputID *string, previousStageOutput *any) {
 	// A current lack of observability into the atp client prevents
 	// non-fragile testing of this function.
 	r.lock.Lock()
@@ -1042,16 +1068,16 @@ func (r *runningStep) transitionStage(newStage StageID, state step.RunningStepSt
 	r.stageChangeHandler.OnStageChange(
 		r,
 		&previousStage,
-		nil,
-		nil,
+		outputID,
+		previousStageOutput,
 		string(newStage),
 		false,
 		&r.wg,
 	)
 }
 
 //nolint:unparam
-func (r *runningStep) completeStage(currentStage StageID, state step.RunningStepState, outputID *string, previousStageOutput *any) {
+func (r *runningStep) completeStep(currentStage StageID, state step.RunningStepState, outputID *string, previousStageOutput *any) {
 	r.lock.Lock()
 	previousStage := string(r.currentStage)
 	r.currentStage = currentStage

internal/step/plugin/provider_test.go

@@ -399,7 +399,7 @@ func TestProvider_VerifyCancelSignal(t *testing.T) {
 	waitStageIDCancelled := waitLifecycle.Stages[waitCancelledStageIDIndex]
 	waitStopIfSchema := assert.MapContainsKey(t, "stop_if", waitStageIDCancelled.InputSchema)
 	if waitStopIfSchema.Disabled {
-		t.Fatalf("step wait's wait_for schema is disabled when the cancel signal is present.")
+		t.Fatalf("step wait's stop_if schema is disabled when the cancel signal is present.")
 	}
 
 	helloLifecycle, err := runnable.Lifecycle(map[string]any{"step": "hello"})

workflow/executor.go

@@ -463,7 +463,7 @@ func (e *executor) createTypeStructure(rootSchema schema.Scope, inputField any,
 			value := v.Index(i).Interface()
 			newValue, err := e.createTypeStructure(rootSchema, value, workflowContext)
 			if err != nil {
-				return nil, fmt.Errorf("failed to resolve expressions (%w)", err)
+				return nil, fmt.Errorf("failed to resolve slice expressions (%w)", err)
 			}
 			result[i] = newValue
 		}
@@ -479,7 +479,7 @@ func (e *executor) createTypeStructure(rootSchema schema.Scope, inputField any,
 			value := v.MapIndex(reflectedKey).Interface()
 			newValue, err := e.createTypeStructure(rootSchema, value, workflowContext)
 			if err != nil {
-				return nil, fmt.Errorf("failed to resolve expressions (%w)", err)
+				return nil, fmt.Errorf("failed to resolve map expressions (%w)", err)
 			}
 			result[keyAsStr] = newValue
 		}

workflow/workflow.go

@@ -524,7 +524,7 @@ func (l *loopState) resolveExpressions(inputData any, dataModel any) (any, error
 			value := v.Index(i).Interface()
 			newValue, err := l.resolveExpressions(value, dataModel)
 			if err != nil {
-				return nil, fmt.Errorf("failed to resolve expressions (%w)", err)
+				return nil, fmt.Errorf("failed to resolve workflow slice expressions (%w)", err)
 			}
 			result[i] = newValue
 		}
@@ -536,7 +536,7 @@ func (l *loopState) resolveExpressions(inputData any, dataModel any) (any, error
 			value := v.MapIndex(reflectedKey).Interface()
 			newValue, err := l.resolveExpressions(value, dataModel)
 			if err != nil {
-				return nil, fmt.Errorf("failed to resolve expressions (%w)", err)
+				return nil, fmt.Errorf("failed to resolve workflow map expressions (%w)", err)
 			}
 			result[key] = newValue
 		}

workflow/workflow_test.go

@@ -346,6 +346,70 @@ func TestWaitForSerial(t *testing.T) {
 	}
 }
 
+var waitForStartedWorkflowDefinition = `
+version: v0.2.0
+input:
+  root: RootObject
+  objects:
+    RootObject:
+      id: RootObject
+      properties: {}
+steps:
+  pre_wait:
+    plugin:
+      src: "n/a"
+      deployment_type: "builtin"
+    step: wait
+    input:
+      wait_time_ms: 2
+  first_wait:
+    plugin:
+      src: "n/a"
+      deployment_type: "builtin"
+    step: wait
+    input:
+      wait_time_ms: 2
+    wait_for: !expr $.steps.pre_wait.outputs
+  second_wait:
+    plugin:
+      src: "n/a"
+      deployment_type: "builtin"
+    step: wait
+    input:
+      wait_time_ms: 2
+    wait_for: !expr $.steps.first_wait.starting.started
+outputs:
+  success:
+    #first_step_output: !expr $.steps.first_wait.outputs
+    second_step_output: !expr $.steps.second_wait.outputs
+`
+
+func TestWaitForStarted(t *testing.T) {
+	// For this test, the second step is depending on a step's running state, which is not a finished output node.
+	logConfig := log.Config{
+		Level:       log.LevelDebug,
+		Destination: log.DestinationStdout,
+	}
+	logger := log.New(
+		logConfig,
+	)
+	cfg := &config.Config{
+		Log: logConfig,
+	}
+	stepRegistry := NewTestImplStepRegistry(logger, t)
+
+	executor := lang.Must2(workflow.NewExecutor(
+		logger,
+		cfg,
+		stepRegistry,
+	))
+	wf := lang.Must2(workflow.NewYAMLConverter(stepRegistry).FromYAML([]byte(waitForStartedWorkflowDefinition)))
+	preparedWorkflow := lang.Must2(executor.Prepare(wf, map[string][]byte{}))
+	outputID, _, err := preparedWorkflow.Execute(context.Background(), map[string]any{})
+	assert.NoError(t, err)
+	assert.Equals(t, outputID, "success")
+}
+
 var missingInputsFailedDeploymentWorkflowDefinition = `
 version: v0.2.0
 input: