Overview: report liveness and a Source whose poll loop stopped

src/app/http.ts

@@ -44,6 +44,8 @@ export interface HttpHost {
   readonly health: Record<string, Health>
   readonly machine: Machine
   readonly masterId: string
+  /** When this process started serving, read by the overview's liveness readout. */
+  readonly startedAt: string
   /** Resolves once startup finishes or setup determines what is still missing. */
   readonly ready: Promise<void>
   /** Resolved deployment; throws if read while waiting for setup (`!configured()`). */
@@ -160,7 +162,7 @@ function routes(runtime: HttpHost): Routes {
   return {
     'GET state': () => stateView(runtime),
     'GET overview': () => overview(views(runtime), runtime.health, policyVersion(store.settings()),
-      executorLoad(store, runtime.executor.activeCount()), runtime.setupProblem ?? runtime.feishuProblem),
+      executorLoad(store, runtime.executor.activeCount()), runtime.setupProblem ?? runtime.feishuProblem, runtime.startedAt),
     'GET search': ({ query }) => search(views(runtime), query.q ?? '', runtime.sourceLinks),
     'GET sources': () => sourcesStatus(views(runtime), runtime.health, setupState(runtime)),
     'GET settings': () => settingsView(store, runtime.sources, runtime.health, setupState(runtime), runtime.machine.stateDir),