chore: restore back to recipients + add test

Signed-off-by: Heikki Hellgren <heikki.hellgren@op.fi>

plugins/signals-react/api-report.md

@@ -27,6 +27,7 @@ export interface SignalSubscriber {
 // @public (undocumented)
 export const useSignal: (channel: string) => {
   lastSignal: JsonObject | null;
+  isSignalsAvailable: boolean;
 };
 
 // (No @packageDocumentation comment for this package)

plugins/signals-react/src/hooks/useSignal.ts

@@ -16,7 +16,7 @@
 import { signalApiRef } from '../api';
 import { useApiHolder } from '@backstage/core-plugin-api';
 import { JsonObject } from '@backstage/types';
-import { useEffect, useState } from 'react';
+import { useEffect, useMemo, useState } from 'react';
 
 /** @public */
 export const useSignal = (channel: string) => {
@@ -40,5 +40,8 @@ export const useSignal = (channel: string) => {
     };
   }, [signals, channel]);
 
-  return { lastSignal };
+  // Can be used to fallback (for example to long polling) if signals are not available in the system
+  const isSignalsAvailable = useMemo(() => !signals, [signals]);
+
+  return { lastSignal, isSignalsAvailable };
 };