simstudioai · icecrasher321 · Mar 19, 2026 · Mar 18, 2026 · Mar 18, 2026 · Mar 18, 2026
diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/subflows/subflow-node.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/subflows/subflow-node.tsx
@@ -168,7 +168,7 @@ export const SubflowNodeComponent = memo(({ data, id, selected }: NodeProps<Subf
           <ActionBar blockId={id} blockType={data.kind} disabled={!userPermissions.canEdit} />
         )}
 
-        {/* Header Section — only interactive area for dragging */}
+        {/* Header Section */}
         <div
           onClick={() => setCurrentBlockId(id)}
           className='workflow-drag-handle flex cursor-grab items-center justify-between rounded-t-[8px] border-[var(--border)] border-b bg-[var(--surface-2)] py-[8px] pr-[12px] pl-[8px] [&:active]:cursor-grabbing'
@@ -198,14 +198,15 @@ export const SubflowNodeComponent = memo(({ data, id, selected }: NodeProps<Subf
         </div>
 
         {/*
-         * Subflow body background. Uses pointer-events: none so that edges rendered
-         * inside the subflow remain clickable. The subflow node wrapper also has
-         * pointer-events: none (set in workflow.tsx), so body-area clicks pass
-         * through to the pane. Subflow selection is done via the header above.
+         * Subflow body background. Captures clicks to select the subflow in the
+         * panel editor, matching the header click behavior. Child nodes and edges
+         * are rendered as sibling divs at the viewport level by ReactFlow (not as
+         * DOM children), so enabling pointer events here doesn't block them.
          */}
         <div
-          className='absolute inset-0 top-[44px] rounded-b-[8px]'
-          style={{ pointerEvents: 'none' }}
+          className='workflow-drag-handle absolute inset-0 top-[44px] cursor-grab rounded-b-[8px] [&:active]:cursor-grabbing'
+          style={{ pointerEvents: isPreview ? 'none' : 'auto' }}
+          onClick={() => setCurrentBlockId(id)}
         />
 
         {!isPreview && (

diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx
@@ -3604,19 +3604,30 @@ const WorkflowContent = React.memo(
 
     /**
      * Handles node click to select the node in ReactFlow.
-     * Parent-child conflict resolution happens automatically in onNodesChange.
+     * Uses the controlled display node state so parent-child conflicts are resolved
+     * consistently for click, shift-click, and marquee selection.
      */
     const handleNodeClick = useCallback(
       (event: React.MouseEvent, node: Node) => {
         const isMultiSelect = event.shiftKey || event.metaKey || event.ctrlKey
-        setNodes((nodes) =>
-          nodes.map((n) => ({
+        selectedIdsRef.current = null
+        setDisplayNodes((nodes) => {
+          const updated = nodes.map((n) => ({
             ...n,
             selected: isMultiSelect ? (n.id === node.id ? true : n.selected) : n.id === node.id,
           }))
-        )
+          const resolved = resolveParentChildSelectionConflicts(updated, blocks)
+          selectedIdsRef.current = resolved
+            .filter((selectedNode) => selectedNode.selected)
+            .map((selectedNode) => selectedNode.id)
+          return resolved
+        })
+        const selectedIds = selectedIdsRef.current as string[] | null
+        if (selectedIds !== null) {
+          syncPanelWithSelection(selectedIds)
+        }
       },
-      [setNodes]
+      [blocks]
     )
 
     /** Handles edge selection with container context tracking and Shift-click multi-selection. */

diff --git a/apps/sim/executor/dag/builder.ts b/apps/sim/executor/dag/builder.ts
@@ -150,9 +150,7 @@ export class DAGBuilder {
     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()}.`
-      )
+      return
     }
 
     const hasConnections = Array.from(sentinelStartNode.outgoingEdges.values()).some((edge) =>

diff --git a/apps/sim/executor/dag/construction/loops.ts b/apps/sim/executor/dag/construction/loops.ts
@@ -8,24 +8,21 @@ const logger = createLogger('LoopConstructor')
 export class LoopConstructor {
   execute(dag: DAG, reachableBlocks: Set<string>): void {
     for (const [loopId, loopConfig] of dag.loopConfigs) {
-      const loopNodes = loopConfig.nodes
-
-      if (loopNodes.length === 0) {
+      if (!reachableBlocks.has(loopId)) {
         continue
       }
 
-      if (!this.hasReachableNodes(loopNodes, reachableBlocks)) {
-        continue
+      const loopNodes = loopConfig.nodes
+      const hasReachableChildren = loopNodes.some((nodeId) => reachableBlocks.has(nodeId))
+
+      if (!hasReachableChildren) {
+        loopConfig.nodes = []
       }
 
       this.createSentinelPair(dag, loopId)
     }
   }
 
-  private hasReachableNodes(loopNodes: string[], reachableBlocks: Set<string>): boolean {
-    return loopNodes.some((nodeId) => reachableBlocks.has(nodeId))
-  }
-
   private createSentinelPair(dag: DAG, loopId: string): void {
     const startId = buildSentinelStartId(loopId)
     const endId = buildSentinelEndId(loopId)

diff --git a/apps/sim/executor/dag/construction/parallels.ts b/apps/sim/executor/dag/construction/parallels.ts
@@ -11,24 +11,21 @@ const logger = createLogger('ParallelConstructor')
 export class ParallelConstructor {
   execute(dag: DAG, reachableBlocks: Set<string>): void {
     for (const [parallelId, parallelConfig] of dag.parallelConfigs) {
-      const parallelNodes = parallelConfig.nodes
-
-      if (parallelNodes.length === 0) {
+      if (!reachableBlocks.has(parallelId)) {
         continue
       }
 
-      if (!this.hasReachableNodes(parallelNodes, reachableBlocks)) {
-        continue
+      const parallelNodes = parallelConfig.nodes
+      const hasReachableChildren = parallelNodes.some((nodeId) => reachableBlocks.has(nodeId))
+
+      if (!hasReachableChildren) {
+        parallelConfig.nodes = []
       }
 
       this.createSentinelPair(dag, parallelId)
     }
   }
 
-  private hasReachableNodes(parallelNodes: string[], reachableBlocks: Set<string>): boolean {
-    return parallelNodes.some((nodeId) => reachableBlocks.has(nodeId))
-  }
-
   private createSentinelPair(dag: DAG, parallelId: string): void {
     const startId = buildParallelSentinelStartId(parallelId)
     const endId = buildParallelSentinelEndId(parallelId)

diff --git a/apps/sim/executor/orchestrators/loop.ts b/apps/sim/executor/orchestrators/loop.ts
@@ -56,6 +56,29 @@ export class LoopOrchestrator {
     if (!loopConfig) {
       throw new Error(`Loop config not found: ${loopId}`)
     }
+
+    if (loopConfig.nodes.length === 0) {
+      const errorMessage =
+        'Loop has no executable blocks inside. Add or enable at least one block in the loop.'
+      const loopType = loopConfig.loopType || 'for'
+      logger.error(errorMessage, { loopId })
+      await this.addLoopErrorLog(ctx, loopId, loopType, errorMessage, {})
+      const errorScope: LoopScope = {
+        iteration: 0,
+        maxIterations: 0,
+        loopType,
+        currentIterationOutputs: new Map(),
+        allIterationOutputs: [],
+        condition: 'false',
+        validationError: errorMessage,
+      }
+      if (!ctx.loopExecutions) {
+        ctx.loopExecutions = new Map()
+      }
+      ctx.loopExecutions.set(loopId, errorScope)
+      throw new Error(errorMessage)
+    }
+
     const scope: LoopScope = {
       iteration: 0,
       currentIterationOutputs: new Map(),
@@ -93,6 +116,24 @@ export class LoopOrchestrator {
 
       case 'forEach': {
         scope.loopType = 'forEach'
+        if (
+          loopConfig.forEachItems === undefined ||
+          loopConfig.forEachItems === null ||
+          loopConfig.forEachItems === ''
+        ) {
+          const errorMessage =
+            'ForEach loop collection is empty. Provide an array or a reference that resolves to a collection.'
+          logger.error(errorMessage, { loopId })
+          await this.addLoopErrorLog(ctx, loopId, loopType, errorMessage, {
+            forEachItems: loopConfig.forEachItems,
+          })
+          scope.items = []
+          scope.maxIterations = 0
+          scope.validationError = errorMessage
+          scope.condition = buildLoopIndexCondition(0)
+          ctx.loopExecutions?.set(loopId, scope)
+          throw new Error(errorMessage)
+        }
         let items: any[]
         try {
           items = resolveArrayInput(ctx, loopConfig.forEachItems, this.resolver)

diff --git a/apps/sim/executor/orchestrators/parallel.ts b/apps/sim/executor/orchestrators/parallel.ts
@@ -57,6 +57,15 @@ export class ParallelOrchestrator {
       throw new Error(`Parallel config not found: ${parallelId}`)
     }
 
+    if (terminalNodesCount === 0 || parallelConfig.nodes.length === 0) {
+      const errorMessage =
+        'Parallel has no executable blocks inside. Add or enable at least one block in the parallel.'
+      logger.error(errorMessage, { parallelId })
+      await this.addParallelErrorLog(ctx, parallelId, errorMessage, {})
+      this.setErrorScope(ctx, parallelId, errorMessage)
+      throw new Error(errorMessage)
+    }
+
     let items: any[] | undefined
     let branchCount: number
     let isEmpty = false
@@ -258,7 +267,9 @@ export class ParallelOrchestrator {
       config.distribution === null ||
       config.distribution === ''
     ) {
-      return []
+      throw new Error(
+        'Parallel collection distribution is empty. Provide an array or a reference that resolves to a collection.'
+      )
     }
     return resolveArrayInput(ctx, config.distribution, this.resolver)
   }