diff --git a/ui/src/components/ProcessDiagram/CompoundNode.tsx b/ui/src/components/ProcessDiagram/CompoundNode.tsx
index eb5f7c33..f1180c3e 100644
--- a/ui/src/components/ProcessDiagram/CompoundNode.tsx
+++ b/ui/src/components/ProcessDiagram/CompoundNode.tsx
@@ -1,5 +1,6 @@
 import type { DiagramNode as DiagramNodeType, DiagramEdge as DiagramEdgeType } from '../../api/queries/diagrams';
 import type { NodeConfig } from './types';
+import type { NodeExecutionState } from '../ExecutionDiagram/types';
 import { colorForType, isCompoundType } from './node-colors';
 import { DiagramNode } from './DiagramNode';
 import { DiagramEdge } from './DiagramEdge';
@@ -17,6 +18,8 @@ interface CompoundNodeProps {
   selectedNodeId?: string;
   hoveredNodeId: string | null;
   nodeConfigs?: Map<string, NodeConfig>;
+  /** Execution overlay for edge traversal coloring */
+  executionOverlay?: Map<string, NodeExecutionState>;
   onNodeClick: (nodeId: string) => void;
   onNodeDoubleClick?: (nodeId: string) => void;
   onNodeEnter: (nodeId: string) => void;
@@ -25,7 +28,7 @@ interface CompoundNodeProps {
 
 export function CompoundNode({
   node, edges, parentX = 0, parentY = 0,
-  selectedNodeId, hoveredNodeId, nodeConfigs,
+  selectedNodeId, hoveredNodeId, nodeConfigs, executionOverlay,
   onNodeClick, onNodeDoubleClick, onNodeEnter, onNodeLeave,
 }: CompoundNodeProps) {
   const x = (node.x ?? 0) - parentX;
@@ -78,15 +81,21 @@ export function CompoundNode({
 
       {/* Internal edges (rendered after background, before children) */}
       <g className="edges">
-        {internalEdges.map((edge, i) => (
-          <DiagramEdge
-            key={`${edge.sourceId}-${edge.targetId}-${i}`}
-            edge={{
-              ...edge,
-              points: edge.points.map(p => [p[0] - absX, p[1] - absY]),
-            }}
-          />
-        ))}
+        {internalEdges.map((edge, i) => {
+          const isTraversed = executionOverlay
+            ? (executionOverlay.has(edge.sourceId) && executionOverlay.has(edge.targetId))
+            : undefined;
+          return (
+            <DiagramEdge
+              key={`${edge.sourceId}-${edge.targetId}-${i}`}
+              edge={{
+                ...edge,
+                points: edge.points.map(p => [p[0] - absX, p[1] - absY]),
+              }}
+              traversed={isTraversed}
+            />
+          );
+        })}
       </g>
 
       {/* Children — recurse into compound children, render leaves as DiagramNode */}
@@ -102,6 +111,7 @@ export function CompoundNode({
               selectedNodeId={selectedNodeId}
               hoveredNodeId={hoveredNodeId}
               nodeConfigs={nodeConfigs}
+              executionOverlay={executionOverlay}
               onNodeClick={onNodeClick}
               onNodeDoubleClick={onNodeDoubleClick}
               onNodeEnter={onNodeEnter}
diff --git a/ui/src/components/ProcessDiagram/DiagramEdge.tsx b/ui/src/components/ProcessDiagram/DiagramEdge.tsx
index 7c6c5a9c..3b0a8b41 100644
--- a/ui/src/components/ProcessDiagram/DiagramEdge.tsx
+++ b/ui/src/components/ProcessDiagram/DiagramEdge.tsx
@@ -3,9 +3,11 @@ import type { DiagramEdge as DiagramEdgeType } from '../../api/queries/diagrams'
 interface DiagramEdgeProps {
   edge: DiagramEdgeType;
   offsetY?: number;
+  /** undefined = no overlay (default gray solid), true = traversed (green solid), false = not traversed (gray dashed) */
+  traversed?: boolean | undefined;
 }
 
-export function DiagramEdge({ edge, offsetY = 0 }: DiagramEdgeProps) {
+export function DiagramEdge({ edge, offsetY = 0, traversed }: DiagramEdgeProps) {
   const pts = edge.points;
   if (!pts || pts.length < 2) return null;
 
@@ -29,9 +31,10 @@ export function DiagramEdge({ edge, offsetY = 0 }: DiagramEdgeProps) {
       <path
         d={d}
         fill="none"
-        stroke="#9CA3AF"
-        strokeWidth={1.5}
-        markerEnd="url(#arrowhead)"
+        stroke={traversed === true ? '#3D7C47' : '#9CA3AF'}
+        strokeWidth={traversed === true ? 1.5 : traversed === false ? 1 : 1.5}
+        strokeDasharray={traversed === false ? '4,3' : undefined}
+        markerEnd={traversed === true ? 'url(#arrowhead-green)' : traversed === false ? undefined : 'url(#arrowhead)'}
       />
       {edge.label && pts.length >= 2 && (
         <text
diff --git a/ui/src/components/ProcessDiagram/ErrorSection.tsx b/ui/src/components/ProcessDiagram/ErrorSection.tsx
index 0ca067ff..43448c6a 100644
--- a/ui/src/components/ProcessDiagram/ErrorSection.tsx
+++ b/ui/src/components/ProcessDiagram/ErrorSection.tsx
@@ -1,6 +1,7 @@
 import { useMemo } from 'react';
 import type { DiagramSection } from './types';
 import type { NodeConfig } from './types';
+import type { NodeExecutionState } from '../ExecutionDiagram/types';
 import type { DiagramNode as DiagramNodeType } from '../../api/queries/diagrams';
 import { DiagramEdge } from './DiagramEdge';
 import { DiagramNode } from './DiagramNode';
@@ -16,6 +17,8 @@ interface ErrorSectionProps {
   selectedNodeId?: string;
   hoveredNodeId: string | null;
   nodeConfigs?: Map<string, NodeConfig>;
+  /** Execution overlay for edge traversal coloring */
+  executionOverlay?: Map<string, NodeExecutionState>;
   onNodeClick: (nodeId: string) => void;
   onNodeDoubleClick?: (nodeId: string) => void;
   onNodeEnter: (nodeId: string) => void;
@@ -28,7 +31,7 @@ const VARIANT_COLORS: Record<string, string> = {
 };
 
 export function ErrorSection({
-  section, totalWidth, selectedNodeId, hoveredNodeId, nodeConfigs,
+  section, totalWidth, selectedNodeId, hoveredNodeId, nodeConfigs, executionOverlay,
   onNodeClick, onNodeDoubleClick, onNodeEnter, onNodeLeave,
 }: ErrorSectionProps) {
   const color = VARIANT_COLORS[section.variant ?? 'error'] ?? VARIANT_COLORS.error;
@@ -82,9 +85,14 @@ export function ErrorSection({
       <g transform={`translate(${CONTENT_PADDING_LEFT}, ${CONTENT_PADDING_Y})`}>
         {/* Edges */}
         <g className="edges">
-          {section.edges.map((edge, i) => (
-            <DiagramEdge key={`${edge.sourceId}-${edge.targetId}-${i}`} edge={edge} />
-          ))}
+          {section.edges.map((edge, i) => {
+            const isTraversed = executionOverlay
+              ? (executionOverlay.has(edge.sourceId) && executionOverlay.has(edge.targetId))
+              : undefined;
+            return (
+              <DiagramEdge key={`${edge.sourceId}-${edge.targetId}-${i}`} edge={edge} traversed={isTraversed} />
+            );
+          })}
         </g>
 
         {/* Nodes */}
@@ -99,6 +107,7 @@ export function ErrorSection({
                   selectedNodeId={selectedNodeId}
                   hoveredNodeId={hoveredNodeId}
                   nodeConfigs={nodeConfigs}
+                  executionOverlay={executionOverlay}
                   onNodeClick={onNodeClick}
                   onNodeDoubleClick={onNodeDoubleClick}
                   onNodeEnter={onNodeEnter}
diff --git a/ui/src/components/ProcessDiagram/ProcessDiagram.tsx b/ui/src/components/ProcessDiagram/ProcessDiagram.tsx
index d9c6bdbc..f63b4ffe 100644
--- a/ui/src/components/ProcessDiagram/ProcessDiagram.tsx
+++ b/ui/src/components/ProcessDiagram/ProcessDiagram.tsx
@@ -53,6 +53,7 @@ export function ProcessDiagram({
   knownRouteIds,
   className,
   diagramLayout,
+  executionOverlay,
 }: ProcessDiagramProps) {
   // Route stack for drill-down navigation
   const [routeStack, setRouteStack] = useState<string[]>([routeId]);
@@ -209,14 +210,29 @@ export function ProcessDiagram({
           >
             <polygon points="0 0, 8 3, 0 6" fill="#9CA3AF" />
           </marker>
+          <marker
+            id="arrowhead-green"
+            markerWidth="8"
+            markerHeight="6"
+            refX="7"
+            refY="3"
+            orient="auto"
+          >
+            <polygon points="0 0, 8 3, 0 6" fill="#3D7C47" />
+          </marker>
         </defs>
 
         <g style={{ transform: zoom.transform, transformOrigin: '0 0' }}>
           {/* Main section top-level edges (not inside compounds) */}
           <g className="edges">
-            {mainSection.edges.filter(e => topLevelEdge(e, mainSection.nodes)).map((edge, i) => (
-              <DiagramEdge key={`${edge.sourceId}-${edge.targetId}-${i}`} edge={edge} />
-            ))}
+            {mainSection.edges.filter(e => topLevelEdge(e, mainSection.nodes)).map((edge, i) => {
+              const isTraversed = executionOverlay
+                ? (executionOverlay.has(edge.sourceId) && executionOverlay.has(edge.targetId))
+                : undefined;
+              return (
+                <DiagramEdge key={`${edge.sourceId}-${edge.targetId}-${i}`} edge={edge} traversed={isTraversed} />
+              );
+            })}
           </g>
 
           {/* Main section nodes */}
@@ -231,6 +247,7 @@ export function ProcessDiagram({
                     selectedNodeId={selectedNodeId}
                     hoveredNodeId={toolbar.hoveredNodeId}
                     nodeConfigs={nodeConfigs}
+                    executionOverlay={executionOverlay}
                     onNodeClick={handleNodeClick}
                     onNodeDoubleClick={handleNodeDoubleClick}
                     onNodeEnter={toolbar.onNodeEnter}
@@ -265,6 +282,7 @@ export function ProcessDiagram({
               selectedNodeId={selectedNodeId}
               hoveredNodeId={toolbar.hoveredNodeId}
               nodeConfigs={nodeConfigs}
+              executionOverlay={executionOverlay}
               onNodeClick={handleNodeClick}
               onNodeDoubleClick={handleNodeDoubleClick}
               onNodeEnter={toolbar.onNodeEnter}