feat: add execution overlay types and extend ProcessDiagram with diagramLayout prop

Define the execution overlay type system (NodeExecutionState, IterationInfo,
DetailTab) and extend ProcessDiagramProps with optional overlay props. Add
diagramLayout prop so ExecutionDiagram can pass a pre-fetched layout by content
hash, bypassing the internal route-based fetch in useDiagramData.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/ProcessDiagram/useDiagramData.ts

@@ -1,6 +1,6 @@
 import { useMemo } from 'react';
 import { useDiagramByRoute } from '../../api/queries/diagrams';
-import type { DiagramNode, DiagramEdge } from '../../api/queries/diagrams';
+import type { DiagramNode, DiagramEdge, DiagramLayout } from '../../api/queries/diagrams';
 import type { DiagramSection } from './types';
 import { isErrorCompoundType, isCompletionCompoundType } from './node-colors';
 
@@ -10,8 +10,14 @@ export function useDiagramData(
   application: string,
   routeId: string,
   direction: 'LR' | 'TB' = 'LR',
+  preloadedLayout?: DiagramLayout,
 ) {
-  const { data: layout, isLoading, error } = useDiagramByRoute(application, routeId, direction);
+  // When a preloaded layout is provided, disable the internal fetch
+  const fetchApp = preloadedLayout ? undefined : application;
+  const fetchRoute = preloadedLayout ? undefined : routeId;
+  const { data: fetchedLayout, isLoading, error } = useDiagramByRoute(fetchApp, fetchRoute, direction);
+
+  const layout = preloadedLayout ?? fetchedLayout;
 
   const result = useMemo(() => {
     if (!layout?.nodes) {
@@ -106,7 +112,11 @@ export function useDiagramData(
     return { sections, totalWidth, totalHeight };
   }, [layout]);
 
-  return { ...result, isLoading, error };
+  return {
+    ...result,
+    isLoading: preloadedLayout ? false : isLoading,
+    error: preloadedLayout ? null : error,
+  };
 }
 
 /** Shift all node coordinates by subtracting an offset, recursively. */