chore: import upstream snapshot with attribution

apps/sim/executor/dag/construction/parallels.ts

@@ -0,0 +1,55 @@
+import { BlockType, PARALLEL } from '@/executor/constants'
+import type { DAG } from '@/executor/dag/builder'
+import { createSubflowSentinelNode } from '@/executor/dag/construction/sentinels'
+import {
+  buildParallelSentinelEndId,
+  buildParallelSentinelStartId,
+} from '@/executor/utils/subflow-utils'
+
+export class ParallelConstructor {
+  execute(dag: DAG, reachableBlocks: Set<string>): void {
+    for (const [parallelId, parallelConfig] of dag.parallelConfigs) {
+      if (!reachableBlocks.has(parallelId)) {
+        continue
+      }
+
+      const parallelNodes = parallelConfig.nodes
+      const hasReachableChildren = parallelNodes.some((nodeId) => reachableBlocks.has(nodeId))
+
+      if (!hasReachableChildren) {
+        parallelConfig.nodes = []
+      }
+
+      this.createSentinelPair(dag, parallelId)
+    }
+  }
+
+  private createSentinelPair(dag: DAG, parallelId: string): void {
+    const startId = buildParallelSentinelStartId(parallelId)
+    const endId = buildParallelSentinelEndId(parallelId)
+
+    dag.nodes.set(
+      startId,
+      createSubflowSentinelNode({
+        id: startId,
+        subflowId: parallelId,
+        subflowType: 'parallel',
+        sentinelType: PARALLEL.SENTINEL.START_TYPE,
+        blockType: BlockType.SENTINEL_START,
+        name: `${PARALLEL.SENTINEL.START_NAME_PREFIX} (${parallelId})`,
+      })
+    )
+
+    dag.nodes.set(
+      endId,
+      createSubflowSentinelNode({
+        id: endId,
+        subflowId: parallelId,
+        subflowType: 'parallel',
+        sentinelType: PARALLEL.SENTINEL.END_TYPE,
+        blockType: BlockType.SENTINEL_END,
+        name: `${PARALLEL.SENTINEL.END_NAME_PREFIX} (${parallelId})`,
+      })
+    )
+  }
+}