fix: remount simple canvas per workflow so fitView tracks the new graph

Switching or creating a workflow could leave the simplified canvas fitted to
the previous graph's bounds (an apparently empty canvas after New workflow).
Keying the canvas's ReactFlowProvider on the workflow id forces a fresh
measure + initial fitView per workflow; the in-place refit still handles
inserts/deletes within one workflow.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/dashboard/app/components/WorkflowNodeEditor.tsx

@@ -3155,6 +3155,7 @@ function InnerEditor({
                             <div className="wf-mobile-simple-canvas" data-testid="wf-mobile-simple-canvas">
                               <WorkflowEditorCatalogContext.Provider value={catalogs}>
                                 <WorkflowSimpleCanvas
+                                  instanceKey={activeWorkflow.id}
                                   nodes={nodesForRender}
                                   edges={edges}
                                   columnNames={columnNameMap}
@@ -3883,6 +3884,7 @@ function InnerEditor({
                   <div className="wf-editor-canvas wf-editor-canvas--simple" ref={canvasRef} tabIndex={-1}>
                     <WorkflowEditorCatalogContext.Provider value={catalogs}>
                       <WorkflowSimpleCanvas
+                        instanceKey={activeWorkflow.id}
                         nodes={nodesForRender}
                         edges={edges}
                         columnNames={columnNameMap}

packages/dashboard/app/components/WorkflowSimpleCanvas.tsx

@@ -368,6 +368,11 @@ function SimpleCanvasAutoFit({
 }
 
 export interface WorkflowSimpleCanvasProps {
+  /** Identity of the workflow being rendered (e.g. its id). Changing it
+   *  remounts the flow so React Flow re-measures and re-fits from scratch —
+   *  switching workflows otherwise leaves a viewport fitted to the PREVIOUS
+   *  graph's bounds (seen as an empty-looking canvas after "New workflow"). */
+  instanceKey: string;
   nodes: FlowNode<WorkflowFlowNodeData>[];
   edges: FlowEdge[];
   /** Column id → display name (v2). Empty map for v1 workflows. */
@@ -388,6 +393,7 @@ export interface WorkflowSimpleCanvasProps {
 }
 
 export function WorkflowSimpleCanvas({
+  instanceKey,
   nodes,
   edges,
   columnNames,
@@ -451,7 +457,7 @@ export function WorkflowSimpleCanvas({
           advanced canvas mounted (CSS-hidden) in list/mobile presentations;
           sharing one store between two ReactFlow instances corrupts node
           measurements and breaks fitView on the visible one. */}
-      <ReactFlowProvider>
+      <ReactFlowProvider key={instanceKey}>
       <SimpleCanvasInsertContext.Provider value={onInsertOnEdge}>
       <ReactFlow
         nodes={displayNodes}