fix: prevent log viewer flicker on ExchangeDetail page

Skip global time range in the logs query key when filtering by
exchangeId (exchange logs are historical, the sliding time window is
irrelevant). Add placeholderData to keep previous results visible
during query key transitions on other pages.

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

ui/src/api/queries/logs.ts

@@ -21,17 +21,24 @@ export function useApplicationLogs(
   const refetchInterval = useRefreshInterval(15_000);
   const { timeRange } = useGlobalFilters();
   const to = options?.toOverride ?? timeRange.end.toISOString();
+  // When filtering by exchangeId, skip the global time range — exchange logs are historical
+  const useTimeRange = !options?.exchangeId;
 
   return useQuery({
-    queryKey: ['logs', application, agentId, timeRange.start.toISOString(), to, options?.limit, options?.exchangeId],
+    queryKey: ['logs', application, agentId,
+      useTimeRange ? timeRange.start.toISOString() : null,
+      useTimeRange ? to : null,
+      options?.limit, options?.exchangeId],
     queryFn: async () => {
       const token = useAuthStore.getState().accessToken;
       const params = new URLSearchParams();
       params.set('application', application!);
       if (agentId) params.set('agentId', agentId);
       if (options?.exchangeId) params.set('exchangeId', options.exchangeId);
-      params.set('from', timeRange.start.toISOString());
-      params.set('to', to);
+      if (useTimeRange) {
+        params.set('from', timeRange.start.toISOString());
+        params.set('to', to);
+      }
       if (options?.limit) params.set('limit', String(options.limit));
       const res = await fetch(`${config.apiBaseUrl}/logs?${params}`, {
         headers: {
@@ -43,6 +50,7 @@ export function useApplicationLogs(
       return res.json() as Promise<LogEntryResponse[]>;
     },
     enabled: !!application,
+    placeholderData: (prev) => prev,
     refetchInterval,
   });
 }