feat: allow network admin to control ephemerality setting

Resolves #92

js/src/hooks/use-stream-particles.ts

@@ -4,7 +4,7 @@ import { useAuthStore } from "@/stores/auth-store";
 import { parseParticlePath, type ParticlePath } from "@/lib/particle-path";
 import type { Particle, StreamProperties } from "@/api/types";
 import { where, Timestamp } from "firebase/firestore";
-import { RECENCY_WINDOW_HOURS } from "@/lib/constants";
+import { useNetwork } from "@/hooks/use-networks";
 
 type StreamParticle = Particle & { type: "stream"; properties: StreamProperties };
 
@@ -27,21 +27,28 @@ export function useStreamParticles(path: ParticlePath): UseStreamParticlesResult
   const { networkId } = parseParticlePath(path);
   const user = useAuthStore((s) => s.user);
   const visibilityScopes = useVisibilityScopes(user?.id, networkId);
+  const network = useNetwork(networkId);
+  const retentionHours = network?.message_retention_hours ?? 24;
 
   const [recencyCutoff, setRecencyCutoff] = useState(() => {
     const d = new Date();
-    d.setHours(d.getHours() - RECENCY_WINDOW_HOURS);
+    d.setHours(d.getHours() - retentionHours);
     return Timestamp.fromDate(d);
   });
 
   useEffect(() => {
+    // Recalculate immediately when retention changes
+    const d = new Date();
+    d.setHours(d.getHours() - retentionHours);
+    setRecencyCutoff(Timestamp.fromDate(d));
+
     const interval = setInterval(() => {
       const d = new Date();
-      d.setHours(d.getHours() - RECENCY_WINDOW_HOURS);
+      d.setHours(d.getHours() - retentionHours);
       setRecencyCutoff(Timestamp.fromDate(d));
     }, 60 * 60 * 1000);
     return () => clearInterval(interval);
-  }, []);
+  }, [retentionHours]);
 
   const { children, isLoading } = useLiveParticleChildren(
     path,