order of ops for validations

apps/sim/executor/dag/builder.ts

@@ -136,18 +136,18 @@ export class DAGBuilder {
     nodes: string[] | undefined,
     type: 'Loop' | 'Parallel'
   ): void {
-    const sentinelStartId =
-      type === 'Loop' ? buildSentinelStartId(id) : buildParallelSentinelStartId(id)
-    const sentinelStartNode = dag.nodes.get(sentinelStartId)
-
-    if (!sentinelStartNode) return
-
     if (!nodes || nodes.length === 0) {
       throw new Error(
         `${type} has no blocks inside. Add at least one block to the ${type.toLowerCase()}.`
       )
     }
 
+    const sentinelStartId =
+      type === 'Loop' ? buildSentinelStartId(id) : buildParallelSentinelStartId(id)
+    const sentinelStartNode = dag.nodes.get(sentinelStartId)
+
+    if (!sentinelStartNode) return
+
     const hasConnections = Array.from(sentinelStartNode.outgoingEdges.values()).some((edge) =>
       nodes.includes(extractBaseBlockId(edge.target))
     )

apps/sim/executor/execution/state.ts

@@ -27,6 +27,8 @@ export interface ParallelScope {
   items?: any[]
   /** Error message if parallel validation failed (e.g., exceeded max branches) */
   validationError?: string
+  /** Whether the parallel has an empty distribution and should be skipped */
+  isEmpty?: boolean
 }
 
 export class ExecutionState implements BlockStateController {

apps/sim/executor/orchestrators/loop.ts

@@ -386,10 +386,10 @@ export class LoopOrchestrator {
       return true
     }
 
-    // forEach: skip if items array is empty
     if (scope.loopType === 'forEach') {
       if (!scope.items || scope.items.length === 0) {
-        logger.info('ForEach loop has empty items, skipping loop body', { loopId })
+        logger.info('ForEach loop has empty collection, skipping loop body', { loopId })
+        this.state.setBlockOutput(loopId, { results: [] }, DEFAULTS.EXECUTION_TIME)
         return false
       }
       return true
@@ -399,6 +399,8 @@ export class LoopOrchestrator {
     if (scope.loopType === 'for') {
       if (scope.maxIterations === 0) {
         logger.info('For loop has 0 iterations, skipping loop body', { loopId })
+        // Set empty output for the loop
+        this.state.setBlockOutput(loopId, { results: [] }, DEFAULTS.EXECUTION_TIME)
         return false
       }
       return true

apps/sim/executor/orchestrators/node.ts

@@ -158,6 +158,17 @@ export class NodeExecutionOrchestrator {
           this.parallelOrchestrator.initializeParallelScope(ctx, parallelId, nodesInParallel)
         }
       }
+
+      const scope = this.parallelOrchestrator.getParallelScope(ctx, parallelId)
+      if (scope?.isEmpty) {
+        logger.info('Parallel has empty distribution, skipping parallel body', { parallelId })
+        return {
+          sentinelStart: true,
+          shouldExit: true,
+          selectedRoute: EDGE.PARALLEL_EXIT,
+        }
+      }
+
       return { sentinelStart: true }
     }
 

apps/sim/executor/orchestrators/parallel.ts

@@ -61,11 +61,13 @@ export class ParallelOrchestrator {
 
     let items: any[] | undefined
     let branchCount: number
+    let isEmpty = false
 
     try {
-      const resolved = this.resolveBranchCount(ctx, parallelConfig)
+      const resolved = this.resolveBranchCount(ctx, parallelConfig, parallelId)
       branchCount = resolved.branchCount
       items = resolved.items
+      isEmpty = resolved.isEmpty ?? false
     } catch (error) {
       const errorMessage = `Parallel Items did not resolve: ${error instanceof Error ? error.message : String(error)}`
       logger.error(errorMessage, { parallelId, distribution: parallelConfig.distribution })
@@ -91,6 +93,34 @@ export class ParallelOrchestrator {
       throw new Error(branchError)
     }
 
+    // Handle empty distribution - skip parallel body
+    if (isEmpty || branchCount === 0) {
+      const scope: ParallelScope = {
+        parallelId,
+        totalBranches: 0,
+        branchOutputs: new Map(),
+        completedCount: 0,
+        totalExpectedNodes: 0,
+        items: [],
+        isEmpty: true,
+      }
+
+      if (!ctx.parallelExecutions) {
+        ctx.parallelExecutions = new Map()
+      }
+      ctx.parallelExecutions.set(parallelId, scope)
+
+      // Set empty output for the parallel
+      this.state.setBlockOutput(parallelId, { results: [] })
+
+      logger.info('Parallel scope initialized with empty distribution, skipping body', {
+        parallelId,
+        branchCount: 0,
+      })
+
+      return scope
+    }
+
     const { entryNodes } = this.expander.expandParallel(this.dag, parallelId, branchCount, items)
 
     const scope: ParallelScope = {
@@ -127,15 +157,17 @@ export class ParallelOrchestrator {
 
   private resolveBranchCount(
     ctx: ExecutionContext,
-    config: SerializedParallel
-  ): { branchCount: number; items?: any[] } {
+    config: SerializedParallel,
+    parallelId: string
+  ): { branchCount: number; items?: any[]; isEmpty?: boolean } {
     if (config.parallelType === 'count') {
       return { branchCount: config.count ?? 1 }
     }
 
     const items = this.resolveDistributionItems(ctx, config)
     if (items.length === 0) {
-      return { branchCount: config.count ?? 1 }
+      logger.info('Parallel has empty distribution, skipping parallel body', { parallelId })
+      return { branchCount: 0, items: [], isEmpty: true }
     }
 
     return { branchCount: items.length, items }