feat: filter to ephemeral streams and particles

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

@@ -1,9 +1,11 @@
-import { useCallback, useEffect, useEffectEvent, useMemo, useReducer, useRef } from "react";
+import { useCallback, useEffect, useEffectEvent, useMemo, useReducer, useRef, useState } from "react";
 import { useAuthStore } from "@/stores/auth-store";
 import type { Particle } from "@/api/types";
 import { useLiveParticleChildren } from "@/hooks/use-particle";
 import { toFirestoreDocPath, type ParticlePath } from "@/lib/particle-path";
 import { updateStreamPlaybackMarker } from "@/lib/firestore-particles";
+import { where, Timestamp } from "firebase/firestore";
+import { RECENCY_WINDOW_HOURS } from "@/lib/constants";
 
 // --- Playback reducer (ID-based) ---
 
@@ -112,8 +114,15 @@ export function useStreamPlayback(
     });
   });
 
+  const [recencyCutoff] = useState(() => {
+    const d = new Date();
+    d.setHours(d.getHours() - RECENCY_WINDOW_HOURS);
+    return Timestamp.fromDate(d);
+  });
+
   const { children } = useLiveParticleChildren(
     path, "created_at", "asc", undefined, onParticleAdded, onParticleRemoved,
+    where("created_at", ">=", recencyCutoff),
   );
 
   // Derive current index and particle from ID