feat(freshness): enhance diagnostics and update snapshot structure

- Introduced a new Diagnostics struct to capture transaction visibility state and activity state.
- Updated BuildSnapshot function to return diagnostics alongside snapshot, completeness, and sampling.
- Enhanced test cases to validate the new diagnostics data.
- Updated frontend components to utilize the new diagnostics information for improved user feedback on freshness context.

This change improves the observability of transaction activity and enhances the user experience by providing clearer insights into the freshness of data.

frontend/src/components/explorer/OperationsHubPage.tsx

@@ -10,6 +10,7 @@ import { summarizeChainActivity } from '@/utils/activityContext'
 import ActivityContextPanel from '@/components/common/ActivityContextPanel'
 import FreshnessTrustNote from '@/components/common/FreshnessTrustNote'
 import { resolveEffectiveFreshness } from '@/utils/explorerFreshness'
+import { statsApi, type ExplorerStats } from '@/services/api/stats'
 
 function relativeAge(isoString?: string): string {
   if (!isoString) return 'Unknown'
@@ -56,6 +57,7 @@ interface OperationsHubPageProps {
   initialNetworksConfig?: NetworksConfigResponse | null
   initialTokenList?: TokenListResponse | null
   initialCapabilities?: CapabilitiesResponse | null
+  initialStats?: ExplorerStats | null
 }
 
 export default function OperationsHubPage({
@@ -64,6 +66,7 @@ export default function OperationsHubPage({
   initialNetworksConfig = null,
   initialTokenList = null,
   initialCapabilities = null,
+  initialStats = null,
 }: OperationsHubPageProps) {
   const { mode } = useUiMode()
   const [bridgeStatus, setBridgeStatus] = useState<MissionControlBridgeStatusResponse | null>(initialBridgeStatus)
@@ -71,6 +74,7 @@ export default function OperationsHubPage({
   const [networksConfig, setNetworksConfig] = useState<NetworksConfigResponse | null>(initialNetworksConfig)
   const [tokenList, setTokenList] = useState<TokenListResponse | null>(initialTokenList)
   const [capabilities, setCapabilities] = useState<CapabilitiesResponse | null>(initialCapabilities)
+  const [stats, setStats] = useState<ExplorerStats | null>(initialStats)
   const [loadingError, setLoadingError] = useState<string | null>(null)
   const page = explorerFeaturePages.operations
 
@@ -78,13 +82,14 @@ export default function OperationsHubPage({
     let cancelled = false
 
     const load = async () => {
-      const [bridgeResult, routesResult, networksResult, tokenListResult, capabilitiesResult] =
+      const [bridgeResult, routesResult, networksResult, tokenListResult, capabilitiesResult, statsResult] =
         await Promise.allSettled([
           missionControlApi.getBridgeStatus(),
           routesApi.getRouteMatrix(),
           configApi.getNetworks(),
           configApi.getTokenList(),
           configApi.getCapabilities(),
+          statsApi.get(),
         ])
 
       if (cancelled) return
@@ -94,6 +99,7 @@ export default function OperationsHubPage({
       if (networksResult.status === 'fulfilled') setNetworksConfig(networksResult.value)
       if (tokenListResult.status === 'fulfilled') setTokenList(tokenListResult.value)
       if (capabilitiesResult.status === 'fulfilled') setCapabilities(capabilitiesResult.value)
+      if (statsResult.status === 'fulfilled') setStats(statsResult.value)
 
       const failedCount = [
         bridgeResult,
@@ -101,9 +107,10 @@ export default function OperationsHubPage({
         networksResult,
         tokenListResult,
         capabilitiesResult,
+        statsResult,
       ].filter((result) => result.status === 'rejected').length
 
-      if (failedCount === 5) {
+      if (failedCount === 6) {
         setLoadingError('Public explorer operations data is temporarily unavailable.')
       }
     }
@@ -153,9 +160,10 @@ export default function OperationsHubPage({
           ? Number(bridgeStatus.data.chains['138'].block_number)
           : null,
         latestBlockTimestamp: null,
-        freshness: resolveEffectiveFreshness(null, bridgeStatus),
+        freshness: resolveEffectiveFreshness(stats, bridgeStatus),
+        diagnostics: stats?.diagnostics ?? bridgeStatus?.data?.diagnostics ?? null,
       }),
-    [bridgeStatus],
+    [bridgeStatus, stats],
   )
 
   return (
@@ -191,6 +199,7 @@ export default function OperationsHubPage({
         <FreshnessTrustNote
           className="mt-3"
           context={activityContext}
+          stats={stats}
           bridgeStatus={bridgeStatus}
           scopeLabel="This page reflects mission-control freshness, public bridge status, and explorer-served config surfaces."
         />