fix(webapp): stop the smart-column sample showing 'No runs' while loading

The sample panel treated 'fetch not finished' the same as 'no runs
found', so it flashed (or stuck on) 'No runs to sample' before the
request resolved. It now shows a loading state until the fetch completes
and reloads on each open, so 'No runs to sample' only appears when there
genuinely are none.

Author: ericallam

apps/webapp/app/components/runs/v3/AddSmartColumnDialog.tsx

@@ -78,14 +78,15 @@ export function AddSmartColumnDialog({
   }, [organization.slug, project.slug, environment.slug, currentSearch]);
 
   useEffect(() => {
-    if (open && sample.state === "idle" && sample.data === undefined) {
+    if (open && sample.state === "idle") {
       sample.load(sampleUrl);
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [open, sampleUrl]);
 
   const effectiveLabel = labelEdited ? label : labelFromPath(path);
 
+  const sampleLoaded = sample.data !== undefined && sample.state === "idle";
   const sampleRuns = sample.data?.runs ?? [];
   const clampedIndex = sampleRuns.length > 0 ? Math.min(sampleIndex, sampleRuns.length - 1) : 0;
   const sampleRun = sampleRuns[clampedIndex] ?? null;
@@ -210,7 +211,7 @@ export function AddSmartColumnDialog({
                   />
                 )}
               </div>
-              {sample.state === "loading" ? (
+              {!sampleLoaded ? (
                 <Paragraph variant="extra-small" className="text-text-dimmed">
                   Loading…
                 </Paragraph>