fix: allow drag-to-pan over diagram nodes and compounds

Previously onPointerDown bailed out when the target was inside a node
(data-node-id), blocking pan entirely over nodes and compound groups.
Now panning always starts, and a didPan ref distinguishes drag from
click — node click handlers skip selection when the user was dragging.

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

ui/src/components/ProcessDiagram/ProcessDiagram.tsx

@@ -152,8 +152,12 @@ export function ProcessDiagram({
   );
 
   const handleNodeClick = useCallback(
-    (nodeId: string) => { onNodeSelect?.(nodeId); },
-    [onNodeSelect],
+    (nodeId: string) => {
+      // Suppress click if the pointer gesture was a drag (pan)
+      if (zoom.didPan.current) return;
+      onNodeSelect?.(nodeId);
+    },
+    [onNodeSelect, zoom.didPan],
   );
 
   const handleNodeDoubleClick = useCallback(

ui/src/components/ProcessDiagram/useZoomPan.ts

@@ -18,6 +18,7 @@ export function useZoomPan() {
     translateY: 0,
   });
   const isPanning = useRef(false);
+  const didPan = useRef(false);
   const panStart = useRef({ x: 0, y: 0 });
   const containerRef = useRef<HTMLDivElement>(null);
   const svgRef = useRef<SVGSVGElement>(null);
@@ -57,8 +58,11 @@ export function useZoomPan() {
 
   const onPointerDown = useCallback(
     (e: React.PointerEvent<SVGSVGElement>) => {
-      if ((e.target as Element).closest('[data-node-id]')) return;
+      // Always allow drag-to-pan, even over nodes. Click vs drag is
+      // distinguished by didPan: if the pointer moved, it's a pan and
+      // node click handlers should be suppressed.
       isPanning.current = true;
+      didPan.current = false;
       panStart.current = { x: e.clientX - state.translateX, y: e.clientY - state.translateY };
       (e.currentTarget as SVGSVGElement).setPointerCapture(e.pointerId);
     },
@@ -68,6 +72,7 @@ export function useZoomPan() {
   const onPointerMove = useCallback(
     (e: React.PointerEvent<SVGSVGElement>) => {
       if (!isPanning.current) return;
+      didPan.current = true;
       setState(prev => ({
         ...prev,
         translateX: e.clientX - panStart.current.x,
@@ -166,6 +171,8 @@ export function useZoomPan() {
     containerRef,
     svgRef,
     transform,
+    /** True if the last pointer gesture was a drag (not a click). Check in click handlers. */
+    didPan,
     panTo,
     resetView,
     onPointerDown,