simstudioai · waleedlatif1 · Aug 12, 2026 · Aug 12, 2026 · Aug 12, 2026 · Aug 12, 2026
diff --git a/...m/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx b/...m/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx
@@ -84,6 +84,10 @@ import {
   useIsBlockInActiveExecutionHandoff,
 } from '@/app/workspace/[workspaceId]/w/[workflowId]/hooks'
 import { useBlockDimensions } from '@/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-dimensions'
+import {
+  isEdgeConnectedToEditor,
+  isEdgeHighlighted,
+} from '@/app/workspace/[workspaceId]/w/[workflowId]/utils/edge-highlight'
 import { hasBlockAccent } from '@/blocks/accent'
 import { useCustomBlockOverlayVersion } from '@/blocks/custom/client-overlay'
 import { getBlock } from '@/blocks/registry'
@@ -716,19 +720,21 @@ export const WorkflowBlock = memo(function WorkflowBlock({
         const keys: string[] = []
         for (const edge of state.edges) {
           if (edge.source !== id && edge.target !== id) continue
-          /*
-           * Must mirror workflow-edge's shouldHighlightEdge exactly: the edge
-           * darkens when an endpoint is canvas-selected OR open in the editor
-           * panel. If the knob checks fewer conditions than the line, a dark
-           * line runs into a light knob.
-           */
-          const isHighlighted =
-            state.nodeInternals.get(edge.source)?.selected ||
-            state.nodeInternals.get(edge.target)?.selected ||
-            (edge.data as { isConnectedToSelection?: boolean } | undefined)
-              ?.isConnectedToSelection ||
-            (editorOpenBlockId !== null &&
-              (edge.source === editorOpenBlockId || edge.target === editorOpenBlockId))
+          /* Same predicate the line itself uses — a knob checking fewer
+             conditions than the edge leaves a dark line running into a light
+             knob. */
+          const isHighlighted = isEdgeHighlighted({
+            isEndpointSelected:
+              state.nodeInternals.get(edge.source)?.selected ||
+              state.nodeInternals.get(edge.target)?.selected ||
+              (edge.data as { isConnectedToSelection?: boolean } | undefined)
+                ?.isConnectedToSelection,
+            isConnectedToEditor: isEdgeConnectedToEditor(
+              editorOpenBlockId,
+              edge.source,
+              edge.target
+            ),
+          })
           if (!isHighlighted) continue
           if (edge.source === id) keys.push(edge.sourceHandle || 'source')
           if (edge.target === id) keys.push(edge.targetHandle || 'target')

diff --git a/...sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-edge/workflow-edge.tsx b/...sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-edge/workflow-edge.tsx
@@ -2,6 +2,10 @@ import { memo, useCallback, useMemo } from 'react'
 import { type EdgeDiffStatus, WorkflowEdgeView } from '@sim/workflow-renderer'
 import { type EdgeProps, useStore } from 'reactflow'
 import { useShallow } from 'zustand/react/shallow'
+import {
+  isEdgeConnectedToEditor,
+  isEdgeHighlighted,
+} from '@/app/workspace/[workspaceId]/w/[workflowId]/utils/edge-highlight'
 import {
   useIsBlockActive,
   useIsCurrentWorkflowExecuting,
@@ -55,11 +59,15 @@ const WorkflowEdgeComponent = (props: WorkflowEdgeProps) => {
     isEndpointSelected ||
       (data as { isConnectedToSelection?: boolean } | undefined)?.isConnectedToSelection
   )
-  const isConnectedToEditor =
-    activeTab === 'editor' &&
-    currentBlockId !== null &&
-    (currentBlockId === source || currentBlockId === target)
-  const shouldHighlightEdge = isConnectedToSelection || isConnectedToEditor
+  const isConnectedToEditor = isEdgeConnectedToEditor(
+    activeTab === 'editor' ? currentBlockId : null,
+    source,
+    target
+  )
+  const shouldHighlightEdge = isEdgeHighlighted({
+    isEndpointSelected: isConnectedToSelection,
+    isConnectedToEditor,
+  })
 
   const previewExecutionStatus = (
     data as { executionStatus?: 'success' | 'error' | 'not-executed' } | undefined

diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/utils/edge-highlight.ts b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/utils/edge-highlight.ts
@@ -0,0 +1,40 @@
+/**
+ * Whether an edge is drawn highlighted.
+ *
+ * Three places need this answer and each reaches it from a different source —
+ * the edge itself from the React Flow store, a card from the same store while
+ * deciding which of its knobs to darken, and the canvas while assigning the
+ * edge's z so a highlighted line is not crossed by an ordinary one. They have
+ * to agree: a knob checking fewer conditions than the line leaves a dark line
+ * running into a light knob, and a z checking fewer leaves the highlight cut in
+ * half by whatever crosses it.
+ *
+ * They agreed by being copied, which is the arrangement that produced both of
+ * those bugs. This is the one definition.
+ */
+export function isEdgeHighlighted(state: {
+  /** Either endpoint is selected on the canvas. */
+  isEndpointSelected?: boolean
+  /** Either endpoint is the block open in the editor panel. */
+  isConnectedToEditor?: boolean
+  /** The edge itself is selected. */
+  isEdgeSelected?: boolean
+}): boolean {
+  return Boolean(state.isEndpointSelected || state.isConnectedToEditor || state.isEdgeSelected)
+}
+
+/**
+ * Whether an edge touches the block currently open in the editor panel.
+ *
+ * `null` while the panel is on another tab, so a block left open behind the
+ * console does not keep its edges lit.
+ */
+export function isEdgeConnectedToEditor(
+  editorOpenBlockId: string | null,
+  source: string,
+  target: string
+): boolean {
+  return (
+    editorOpenBlockId !== null && (source === editorOpenBlockId || target === editorOpenBlockId)
+  )
+}
diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx
@@ -93,6 +93,10 @@ import {
   shouldHighlightContainerDropTarget,
   validateTriggerPaste,
 } from '@/app/workspace/[workspaceId]/w/[workflowId]/utils'
+import {
+  isEdgeConnectedToEditor,
+  isEdgeHighlighted,
+} from '@/app/workspace/[workspaceId]/w/[workflowId]/utils/edge-highlight'
 import {
   defaultEdgeOptions,
   edgeTypes,
@@ -127,7 +131,7 @@ import {
 } from '@/stores/execution'
 import { useSearchModalStore } from '@/stores/modals/search/store'
 import type { PendingConnect } from '@/stores/modals/search/types'
-import { usePanelEditorStore } from '@/stores/panel'
+import { usePanelEditorStore, usePanelStore } from '@/stores/panel'
 import { useUndoRedoStore } from '@/stores/undo-redo'
 import { useVariablesModalStore } from '@/stores/variables/modal'
 import { useWorkflowDiffStore } from '@/stores/workflow-diff/store'
@@ -4461,6 +4465,11 @@ const WorkflowContent = React.memo(
     }, [closeConnectionBlockSelector, displayNodes, lastInteractedNodeId, pendingConnect])
 
     /** Transforms edges to include selection state and delete handlers. Memoized to prevent re-renders. */
+    /* Subscribed rather than read from `getState()`: the edge z below depends on
+       which block is open, so the memo has to re-run when that changes. */
+    const editorOpenBlockId = usePanelEditorStore((state) => state.currentBlockId)
+    const panelActiveTab = usePanelStore((state) => state.activeTab)
+
     const edgesWithSelection = useMemo(() => {
       const nodeMap = new Map(displayNodes.map((n) => [n.id, n]))
       /* Indexed once: this memo re-runs on every drag frame, and scanning the
@@ -4478,21 +4487,38 @@ const WorkflowContent = React.memo(
         // pointer events, so the edge has to be above it to stay clickable) and
         // still below that container's own children.
         //
+        // A highlighted edge takes the top of that band instead, so no ordinary
+        // edge can cross over the one the user has picked out. Depth only ever
+        // ordered lines against each other, and an unselected edge one level
+        // deeper was painting straight through the highlight.
+        //
         // Edges are NEVER elevated above cards — not even when an endpoint is
         // selected. A line always passes behind cards, knobs, and the action
         // bar swell; elevating highlighted edges drew them across their own
-        // endpoint's chrome.
+        // endpoint's chrome. The highlighted tier stays inside the band for
+        // exactly that reason.
         const containerNode = parentLoopId ? nodeMap.get(parentLoopId) : null
-        const baseZIndex = getEdgeZIndex(containerNode ? (containerNode.zIndex ?? 0) : undefined)
         const isConnectedToSelection =
           selectedNodeIdSet.has(edge.source) || selectedNodeIdSet.has(edge.target)
+        const isSelected = selectedEdges.has(edgeContextId)
+        const baseZIndex = getEdgeZIndex(containerNode ? (containerNode.zIndex ?? 0) : undefined, {
+          isHighlighted: isEdgeHighlighted({
+            isEndpointSelected: isConnectedToSelection,
+            isConnectedToEditor: isEdgeConnectedToEditor(
+              panelActiveTab === 'editor' ? editorOpenBlockId : null,
+              edge.source,
+              edge.target
+            ),
+            isEdgeSelected: isSelected,
+          }),
+        })
 
         return {
           ...edge,
           zIndex: baseZIndex,
           data: {
             ...edge.data,
-            isSelected: selectedEdges.has(edgeContextId),
+            isSelected,
             isConnectedToSelection,
             isInsideLoop: Boolean(parentLoopId),
             parentLoopId,
@@ -4501,7 +4527,15 @@ const WorkflowContent = React.memo(
           },
         }
       })
-    }, [edgesForDisplay, displayNodes, selectedNodeIds, selectedEdges, handleEdgeDelete])
+    }, [
+      edgesForDisplay,
+      displayNodes,
+      selectedNodeIds,
+      selectedEdges,
+      handleEdgeDelete,
+      editorOpenBlockId,
+      panelActiveTab,
+    ])
 
     const edgesForRender = useMemo(() => {
       if (!pendingConnect) return edgesWithSelection
@@ -4520,7 +4554,12 @@ const WorkflowContent = React.memo(
           target: CONNECTION_BLOCK_SELECTOR_NODE_ID,
           targetHandle: 'target',
           type: 'workflowEdge',
-          zIndex: getEdgeZIndex(sourceParentNode ? (sourceParentNode.zIndex ?? 0) : undefined),
+          /* Rendered highlighted (`isConnectedToSelection` below), so it is
+             elevated like any other highlighted edge — the preview line is the
+             one the user is currently drawing. */
+          zIndex: getEdgeZIndex(sourceParentNode ? (sourceParentNode.zIndex ?? 0) : undefined, {
+            isHighlighted: true,
+          }),
           focusable: false,
           deletable: false,
           reconnectable: false,

diff --git a/packages/workflow-renderer/src/canvas-layers.test.ts b/packages/workflow-renderer/src/canvas-layers.test.ts
@@ -0,0 +1,71 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it } from 'vitest'
+import {
+  BLOCK_Z_BASE,
+  CONTAINER_CHILD_Z_BASE,
+  EDGE_Z_BASE,
+  EDGE_Z_MAX,
+  getBlockZIndex,
+  getEdgeZIndex,
+} from './canvas-layers'
+
+/**
+ * Nesting depths an edge is tiered by. Stops short of the band's ceiling: past
+ * it every edge saturates at the same tier, which is checked on its own below.
+ */
+const DEPTHS = [undefined, 0, 1, 2, 5]
+
+describe('getEdgeZIndex', () => {
+  it('puts a highlighted edge over every ordinary one, however deeply nested', () => {
+    /* The reported bug: a highlighted edge kept its own container's depth, so an
+       ordinary edge one level deeper painted over it and cut the highlight. */
+    const highlighted = getEdgeZIndex(undefined, { isHighlighted: true })
+
+    for (const depth of DEPTHS) {
+      expect(getEdgeZIndex(depth)).toBeLessThan(highlighted)
+    }
+  })
+
+  it('keeps a highlighted edge below the cards', () => {
+    /* Elevating highlighted edges over the cards drew them across the chrome of
+       their own endpoints, so the highlighted tier stays inside the edge band. */
+    const highlighted = getEdgeZIndex(undefined, { isHighlighted: true })
+
+    expect(highlighted).toBeLessThan(BLOCK_Z_BASE)
+    expect(highlighted).toBeLessThan(getBlockZIndex(BLOCK_Z_BASE))
+    expect(highlighted).toBeLessThan(CONTAINER_CHILD_Z_BASE)
+  })
+
+  it('leaves the in-flight connection line above everything in the band', () => {
+    expect(getEdgeZIndex(undefined, { isHighlighted: true })).toBeLessThan(EDGE_Z_MAX)
+    for (const depth of DEPTHS) {
+      expect(getEdgeZIndex(depth)).toBeLessThan(EDGE_Z_MAX)
+    }
+  })
+
+  it('still orders ordinary edges by the depth they are nested at', () => {
+    expect(getEdgeZIndex(undefined)).toBe(EDGE_Z_BASE)
+    expect(getEdgeZIndex(0)).toBeGreaterThan(getEdgeZIndex(undefined))
+    expect(getEdgeZIndex(1)).toBeGreaterThan(getEdgeZIndex(0))
+  })
+
+  it('keeps every edge clear of the container bodies it crosses', () => {
+    /* Containers are numbered from 0 by nesting depth; an edge sharing a body's
+       z loses the equal-z tiebreak to DOM order and is drawn behind it. */
+    for (const depth of DEPTHS) {
+      expect(getEdgeZIndex(depth)).toBeGreaterThan(depth ?? 0)
+      expect(getEdgeZIndex(depth, { isHighlighted: true })).toBeGreaterThan(depth ?? 0)
+    }
+  })
+
+  it('saturates rather than growing past the band', () => {
+    /* The band is fixed, so beyond its ceiling every edge shares the deepest
+       tier and no longer clears a container nested that far — true before this
+       change too, at a ceiling of `EDGE_Z_MAX` rather than one below the
+       highlighted tier. Nothing in the editor nests anywhere near it. */
+    expect(getEdgeZIndex(40)).toBe(getEdgeZIndex(8))
+    expect(getEdgeZIndex(8)).toBeLessThan(getEdgeZIndex(undefined, { isHighlighted: true }))
+  })
+})
diff --git a/packages/workflow-renderer/src/canvas-layers.ts b/packages/workflow-renderer/src/canvas-layers.ts
@@ -21,6 +21,23 @@
  * once already and took the preview's edges behind its containers with it.
  */
 export const EDGE_Z_BASE = 10
+/**
+ * Deepest nesting tier an ordinary edge reaches, leaving the top of the band to
+ * the two edges that have to be seen whole.
+ */
+const EDGE_Z_DEPTH_MAX = 18
+/**
+ * A highlighted edge — selected, or connected to the selected card. Above every
+ * ordinary edge whatever it is nested in, because the highlight is what the
+ * user is looking at and a line crossing it from a deeper container was cutting
+ * it in half.
+ *
+ * Still inside the edge band, deliberately. Highlighted edges used to be
+ * elevated over the cards as well, which drew them across the chrome of their
+ * own endpoints; a line belongs behind cards, knobs and the action-bar swell
+ * whether or not it is highlighted.
+ */
+const EDGE_Z_HIGHLIGHTED = 19
 export const EDGE_Z_MAX = 20
 export const BLOCK_Z_BASE = 21
 export const CONTAINER_CHILD_Z_BASE = 1000
@@ -41,10 +58,19 @@ export function getBlockZIndex(
  * it belongs to, so an edge always clears the container body it crosses while
  * staying under that container's own children.
  *
+ * A highlighted edge leaves that ordering and takes {@link EDGE_Z_HIGHLIGHTED}
+ * instead. Depth is only a tiebreak between lines nobody is looking at; once one
+ * is highlighted, being drawn whole matters more than which container it came
+ * from — an unselected edge one level deeper used to paint straight over it.
+ *
  * `containerZIndex` is the parent container's own z (its nesting depth), or
  * undefined for an edge at the top level.
  */
-export function getEdgeZIndex(containerZIndex: number | undefined): number {
+export function getEdgeZIndex(
+  containerZIndex: number | undefined,
+  state: { isHighlighted?: boolean } = {}
+): number {
+  if (state.isHighlighted) return EDGE_Z_HIGHLIGHTED
   const depth = containerZIndex === undefined ? 0 : containerZIndex + 1
-  return Math.min(EDGE_Z_BASE + depth, EDGE_Z_MAX)
+  return Math.min(EDGE_Z_BASE + depth, EDGE_Z_DEPTH_MAX)
 }