Improve useful default workbench context

frontend/src/components/detection/DetectionLab.tsx

@@ -143,6 +143,12 @@ export function DetectionLab({
       <div className="lab-block">
         <div className="ai-lab-run-surface" aria-label="Detection run controls">
           <h3>Run detection</h3>
+          {rasterDatasets.length === 0 ? (
+            <div className="result-state result-state-empty">
+              <strong>No raster datasets available for detection.</strong>
+              <p>Upload or select a raster dataset in Data before running object detection.</p>
+            </div>
+          ) : null}
           <div className="lab-form-grid">
             <label>
               Raster dataset

frontend/src/components/segmentation/SegmentationLab.tsx

@@ -143,6 +143,12 @@ export function SegmentationLab({
       <div className="lab-block">
         <div className="ai-lab-run-surface" aria-label="Segmentation run controls">
           <h3>Run segmentation</h3>
+          {rasterDatasets.length === 0 ? (
+            <div className="result-state result-state-empty">
+              <strong>No raster datasets available for segmentation.</strong>
+              <p>Upload or select a raster dataset in Data before running segmentation.</p>
+            </div>
+          ) : null}
           <div className="lab-form-grid">
             <label>
               Raster dataset

frontend/src/hooks/useDatasetWorkflow.ts

@@ -83,6 +83,20 @@ export function useDatasetWorkflow({
     }
   }, [areas, selectedClipAreaId])
 
+  useEffect(() => {
+    if (!selectedProjectId || selectedDatasetId || datasets.length === 0) {
+      return
+    }
+    // Auto-open the first usable dataset so Data, Map and Exports start with real context.
+    const defaultDataset =
+      datasets.find((dataset) => isVectorDatasetType(dataset.dataset_type) && dataset.status === 'ready') ??
+      datasets.find((dataset) => dataset.status === 'ready') ??
+      datasets[0]
+    if (defaultDataset) {
+      loadDatasetDetails(selectedProjectId, defaultDataset).catch(() => null)
+    }
+  }, [datasets, isVectorDatasetType, selectedDatasetId, selectedProjectId])
+
   const loadDatasetJobs = async (projectId: string, datasetId: string) => {
     const response = await jobsApi.list(projectId, { dataset_id: datasetId, limit: 20, offset: 0 })
     setJobs(response.items)