diff --git a/js/desktop/src/components/audio/use-audio-source.ts b/js/desktop/src/components/audio/use-audio-source.ts
index 7c4071b..13ac7b5 100644
--- a/js/desktop/src/components/audio/use-audio-source.ts
+++ b/js/desktop/src/components/audio/use-audio-source.ts
@@ -21,42 +21,45 @@ export function useAudioSource(
   >(new WeakMap());
 
   useEffect(() => {
-    if (!source) {
-      setAudioSource(null);
-      return;
-    }
+    // Build the source node (creating an AudioContext as needed) plus optional
+    // teardown for contexts we own; the branches converge on one setState.
+    let result: AudioSource | null = null;
+    let cleanup: (() => void) | undefined;
 
     if (source instanceof MediaStream) {
       const ctx = new AudioContext();
       ctx.resume();
       const sourceNode = ctx.createMediaStreamSource(source);
-      setAudioSource({ sourceNode, ctx });
-
-      return () => {
-        ctx.close();
-      };
+      result = { sourceNode, ctx };
+      cleanup = () => ctx.close();
+    } else if (source) {
+      // HTMLAudioElement — createMediaElementSource can only be called once per
+      // element, so reuse a cached context/node when we have one.
+      const cached = elementSourceCache.current.get(source);
+      if (cached) {
+        cached.ctx.resume();
+        result = cached;
+      } else {
+        const ctx = new AudioContext();
+        ctx.resume();
+        const sourceNode = ctx.createMediaElementSource(source);
+        // Connect element source to destination so audio is still audible
+        sourceNode.connect(ctx.destination);
+        elementSourceCache.current.set(source, { sourceNode, ctx });
+        result = { sourceNode, ctx };
+        cleanup = () => {
+          ctx.close();
+          elementSourceCache.current.delete(source);
+        };
+      }
     }
 
-    // HTMLAudioElement — createMediaElementSource can only be called once per element
-    const cached = elementSourceCache.current.get(source);
-    if (cached) {
-      cached.ctx.resume();
-      setAudioSource(cached);
-      return;
-    }
+    // Publishing an imperatively-created Web Audio node — external-resource
+    // sync, not a re-render cascade.
+    // eslint-disable-next-line react-hooks/set-state-in-effect
+    setAudioSource(result);
 
-    const ctx = new AudioContext();
-    ctx.resume();
-    const sourceNode = ctx.createMediaElementSource(source);
-    // Connect element source to destination so audio is still audible
-    sourceNode.connect(ctx.destination);
-    elementSourceCache.current.set(source, { sourceNode, ctx });
-    setAudioSource({ sourceNode, ctx });
-
-    return () => {
-      ctx.close();
-      elementSourceCache.current.delete(source);
-    };
+    return cleanup;
   }, [source]);
 
   return audioSource;
diff --git a/js/desktop/src/components/screen-source-picker.tsx b/js/desktop/src/components/screen-source-picker.tsx
index 7a11b15..58e145d 100644
--- a/js/desktop/src/components/screen-source-picker.tsx
+++ b/js/desktop/src/components/screen-source-picker.tsx
@@ -23,16 +23,13 @@ export function ScreenSourcePicker({
     getSources().then((result) => {
       setSources(result);
       setLoading(false);
+      // Auto-select if there's only one source.
+      if (result.length === 1) {
+        setSelectedId(result[0].id);
+      }
     });
   }, [getSources]);
 
-  // Auto-select if there's only one source
-  useEffect(() => {
-    if (!loading && sources.length === 1) {
-      setSelectedId(sources[0].id);
-    }
-  }, [loading, sources]);
-
   const screens = sources.filter((s) => s.id.startsWith("screen:"));
   const windows = sources.filter((s) => s.id.startsWith("window:"));
 
diff --git a/js/desktop/src/features/attachments/attachment-lightbox.tsx b/js/desktop/src/features/attachments/attachment-lightbox.tsx
index 77ea49e..700a561 100644
--- a/js/desktop/src/features/attachments/attachment-lightbox.tsx
+++ b/js/desktop/src/features/attachments/attachment-lightbox.tsx
@@ -1,4 +1,4 @@
-import { useEffect, useState } from "react";
+import { useCallback, useEffect } from "react";
 import { Dialog as DialogPrimitive } from "radix-ui";
 import {
   ChevronLeft,
@@ -10,6 +10,7 @@ import {
   X,
 } from "lucide-react";
 import { useDownloadUrl } from "@/hooks/use-download-url";
+import { useObjectUrl } from "@/hooks/use-object-url";
 import { Button } from "@/components/ui/button";
 import { useSuspendPlayback } from "@/hooks/use-suspend-playback";
 import { platform } from "@/lib/platform";
@@ -71,17 +72,10 @@ export function AttachmentLightbox({
   const { data: remoteUrl, isLoading: isRemoteLoading } =
     useDownloadUrl(remoteObjectId);
 
-  // Local items get a fresh blob URL per item, revoked on change/close.
-  const [localUrl, setLocalUrl] = useState<string | null>(null);
-  useEffect(() => {
-    if (current?.source.kind !== "local") {
-      setLocalUrl(null);
-      return;
-    }
-    const url = URL.createObjectURL(current.source.file);
-    setLocalUrl(url);
-    return () => URL.revokeObjectURL(url);
-  }, [current?.id, current?.source.kind]);
+  // Local items resolve to a blob URL; remote items use the signed-URL cache.
+  const localFile =
+    current?.source.kind === "local" ? current.source.file : null;
+  const localUrl = useObjectUrl(localFile);
 
   const url =
     current?.source.kind === "remote"
@@ -90,18 +84,21 @@ export function AttachmentLightbox({
 
   const canDownload = current?.source.kind === "remote" && !!url;
 
-  const goTo = (delta: number) => {
-    if (openIndex === null || items.length === 0) return;
-    const next = (openIndex + delta + items.length) % items.length;
-    onOpenChange(next);
-  };
+  const goTo = useCallback(
+    (delta: number) => {
+      if (openIndex === null || items.length === 0) return;
+      const next = (openIndex + delta + items.length) % items.length;
+      onOpenChange(next);
+    },
+    [openIndex, items.length, onOpenChange],
+  );
 
-  const handleDownload = () => {
+  const handleDownload = useCallback(() => {
     if (!current || !url || current.source.kind !== "remote") return;
     platform.attachment.download(url, current.filename);
-  };
+  }, [current, url]);
 
-  const handleRemove = () => {
+  const handleRemove = useCallback(() => {
     if (!current || !onRemove) return;
     const wasLast = items.length <= 1;
     const wasAtEnd = openIndex === items.length - 1;
@@ -112,7 +109,7 @@ export function AttachmentLightbox({
       onOpenChange(items.length - 2);
     }
     // Otherwise openIndex stays — the next item shifts into its place.
-  };
+  }, [current, onRemove, items.length, openIndex, onOpenChange]);
 
   useSuspendPlayback(isOpen, "attachment-lightbox");
 
@@ -154,7 +151,7 @@ export function AttachmentLightbox({
     };
     window.addEventListener("keydown", handle, true);
     return () => window.removeEventListener("keydown", handle, true);
-  }, [isOpen, openIndex, items, url, onOpenChange, onRemove, hasMultiple, canDownload]);
+  }, [isOpen, onOpenChange, onRemove, hasMultiple, canDownload, goTo, handleDownload, handleRemove]);
 
   const isImage = current?.mimeType.startsWith("image/");
   const isVideo = current?.mimeType.startsWith("video/");
diff --git a/js/desktop/src/features/compose/compose-overlay.tsx b/js/desktop/src/features/compose/compose-overlay.tsx
index 8657b44..6a17763 100644
--- a/js/desktop/src/features/compose/compose-overlay.tsx
+++ b/js/desktop/src/features/compose/compose-overlay.tsx
@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useEffectEvent, useRef, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 import { toast } from "sonner";
 import { useAuthStore } from "@/stores/auth-store";
 import { useCreateParticle, useCreateStreamParticle } from "@/hooks/use-create-particle";
@@ -80,15 +80,17 @@ export function ComposeOverlay({
   const invalidateUsage = useInvalidateNetworkUsage();
   const quotaExhausted = isUsageExhausted(usage);
 
-  // Refs for synchronous reads in keyboard handlers
+  // Latest props/state for synchronous reads in keyboard handlers.
   const stepRef = useRef(step);
   const recordStartRef = useRef(0);
   const disabledRef = useRef(disabled);
-  disabledRef.current = disabled;
   const quotaExhaustedRef = useRef(quotaExhausted);
-  quotaExhaustedRef.current = quotaExhausted;
   const recordingSourceRef = useRef(recordingSource);
-  recordingSourceRef.current = recordingSource;
+  useEffect(() => {
+    disabledRef.current = disabled;
+    quotaExhaustedRef.current = quotaExhausted;
+    recordingSourceRef.current = recordingSource;
+  }, [disabled, quotaExhausted, recordingSource]);
 
   const setStepSync = useCallback((next: ComposeStep) => {
     stepRef.current = next;
@@ -361,8 +363,8 @@ export function ComposeOverlay({
     return false;
   }, [cancel]);
 
-  // Reply mode: create particle directly under targetPath
-  const onSubmitReply = useEffectEvent(async () => {
+  // Reply mode: create particle directly under targetPath.
+  const onSubmitReply = useCallback(async () => {
     if (!targetPath || !userId || stepRef.current === "submitting") return;
     setStepSync("submitting");
     try {
@@ -371,7 +373,7 @@ export function ComposeOverlay({
     } catch (err) {
       if (!handleQuotaError(err)) throw err;
     }
-  });
+  }, [targetPath, userId, setStepSync, createChildParticle, cancel, handleQuotaError]);
 
   // New stream mode: create stream + first child
   const handleStreamSubmit = useCallback(
@@ -397,7 +399,7 @@ export function ComposeOverlay({
         if (!handleQuotaError(err)) throw err;
       }
     },
-    [networkId, userId, createStream, createChildParticle, cancel, handleQuotaError],
+    [networkId, userId, createStream, createChildParticle, cancel, handleQuotaError, setStepSync],
   );
 
   // --- Compose intent handlers ---
@@ -468,20 +470,25 @@ export function ComposeOverlay({
   // executes the matching handler and clears the intent. Keyboard handlers
   // call the same handlers directly without a store round-trip.
 
-  const intent = useComposeIntentStore((s) => s.intent);
   const clearIntent = useComposeIntentStore((s) => s.clear);
 
+  // Consume fire-and-forget intents from the external store. Reacting in the
+  // store subscription (not an effect body) keeps these state-updating handlers
+  // off the render path and avoids an extra dispatch→render bounce.
   useEffect(() => {
-    if (!intent) return;
-    switch (intent.kind) {
-      case "record": handleRecordIntent(); break;
-      case "text": handleTextIntent(); break;
-      case "stop": handleStopIntent(); break;
-      case "cancel": handleCancelIntent(); break;
-      case "send": handleSendIntent(); break;
-    }
-    clearIntent();
-  }, [intent, handleRecordIntent, handleTextIntent, handleStopIntent, handleCancelIntent, handleSendIntent, clearIntent]);
+    return useComposeIntentStore.subscribe((state, prev) => {
+      const intent = state.intent;
+      if (!intent || intent === prev.intent) return;
+      switch (intent.kind) {
+        case "record": handleRecordIntent(); break;
+        case "text": handleTextIntent(); break;
+        case "stop": handleStopIntent(); break;
+        case "cancel": handleCancelIntent(); break;
+        case "send": handleSendIntent(); break;
+      }
+      clearIntent();
+    });
+  }, [handleRecordIntent, handleTextIntent, handleStopIntent, handleCancelIntent, handleSendIntent, clearIntent]);
 
   // --- Keyboard handling ---
 
diff --git a/js/desktop/src/features/compose/recording-overlay.tsx b/js/desktop/src/features/compose/recording-overlay.tsx
index fbdcf02..c35f785 100644
--- a/js/desktop/src/features/compose/recording-overlay.tsx
+++ b/js/desktop/src/features/compose/recording-overlay.tsx
@@ -3,6 +3,7 @@ import { Paperclip } from "lucide-react";
 import type { RecordingMode } from "@/hooks/use-recording-mode";
 import { AudioLevelBars } from "@/components/audio/audio-level-bars";
 import { useAudioSource } from "@/components/audio/use-audio-source";
+import { useObjectUrl } from "@/hooks/use-object-url";
 import { AttachmentStrip } from "@/features/compose/attachment-strip";
 import type { PendingAttachment } from "@/features/compose/attachment-strip";
 import { cn } from "@/lib/utils";
@@ -65,23 +66,11 @@ function ReviewPlayback({
   mirror?: boolean;
   objectFit?: "cover" | "contain";
 }) {
-  const urlRef = useRef<string | null>(null);
-  const [objectUrl, setObjectUrl] = useState<string | null>(null);
+  const objectUrl = useObjectUrl(blob);
   const audioElRef = useRef<HTMLAudioElement | null>(null);
   const [audioEl, setAudioEl] = useState<HTMLAudioElement | null>(null);
   const audioSource = useAudioSource(isVideo ? null : audioEl);
 
-  useEffect(() => {
-    const url = URL.createObjectURL(blob);
-    urlRef.current = url;
-    setObjectUrl(url);
-
-    return () => {
-      URL.revokeObjectURL(url);
-      urlRef.current = null;
-    };
-  }, [blob]);
-
   if (!objectUrl) return null;
 
   if (isVideo) {
diff --git a/js/desktop/src/features/particles/media-particle-view.tsx b/js/desktop/src/features/particles/media-particle-view.tsx
index 21ba7c3..62b4b07 100644
--- a/js/desktop/src/features/particles/media-particle-view.tsx
+++ b/js/desktop/src/features/particles/media-particle-view.tsx
@@ -33,22 +33,19 @@ export const MediaParticleView = forwardRef<MediaParticleHandle, MediaParticleVi
   onEnded,
   onProgress,
 }, ref) {
-  // Prefer the worker-produced iOS-playable variant when present so desktop
-  // and mobile read the same canonical asset. Falls back to the original.
-  // Pin the choice for the lifetime of this particle: if a transcoded variant
-  // arrives via Firestore mid-playback, swapping the <video> src would restart
-  // playback from 0. Keep whatever we picked first; the original plays fine in
-  // Electron, and the transcoded variant will be picked up on the next view.
-  const pickedSourceRef = useRef<{ id: string; objectId: string; mime: string } | null>(null);
-  if (pickedSourceRef.current?.id !== particle.id) {
-    pickedSourceRef.current = {
-      id: particle.id,
-      objectId: particle.properties.transcoded_object_id ?? particle.properties.object_id,
-      mime: particle.properties.transcoded_mime_type ?? particle.properties.mime_type,
-    };
-  }
-  const activeObjectId = pickedSourceRef.current.objectId;
-  const activeMime = pickedSourceRef.current.mime;
+  // Prefer the worker-produced iOS-playable variant when present so desktop and
+  // mobile read the same canonical asset, falling back to the original. Pinned
+  // on mount (the parent keys this component by particle.id, so a new particle
+  // remounts and re-picks): if a transcoded variant arrives via Firestore for
+  // the same particle, swapping the <video> src would restart playback from 0.
+  const [pickedSource] = useState(() => ({
+    objectId:
+      particle.properties.transcoded_object_id ?? particle.properties.object_id,
+    mime:
+      particle.properties.transcoded_mime_type ?? particle.properties.mime_type,
+  }));
+  const activeObjectId = pickedSource.objectId;
+  const activeMime = pickedSource.mime;
   const { data: url, error } = useDownloadUrl(activeObjectId);
   const { attachments } = useParticleAttachments(streamPath, particle.id);
 
diff --git a/js/desktop/src/features/particles/particle-list-view.tsx b/js/desktop/src/features/particles/particle-list-view.tsx
index 3aa9a58..7e15a1c 100644
--- a/js/desktop/src/features/particles/particle-list-view.tsx
+++ b/js/desktop/src/features/particles/particle-list-view.tsx
@@ -1,4 +1,4 @@
-import { useMemo, useRef, useEffect, useCallback, memo } from "react";
+import { useMemo, useRef, useEffect, useCallback, memo, createElement } from "react";
 import { useNavigate } from "react-router-dom";
 import {
   Radio,
@@ -186,7 +186,9 @@ const StreamRow = memo(function StreamRow({
     ? getMessagePreview(latestChild)
     : particle.properties.name;
 
-  const TypeIcon = latestChild ? getParticleTypeIcon(latestChild) : Radio;
+  // Rendered via createElement below: a call-result used directly as a JSX tag
+  // is flagged as a dynamically-created component.
+  const typeIcon = latestChild ? getParticleTypeIcon(latestChild) : Radio;
 
   const videoThumbObjectId =
     latestChild &&
@@ -254,12 +256,12 @@ const StreamRow = memo(function StreamRow({
           </div>
         </div>
         <div className="flex items-center gap-1">
-          <TypeIcon
-            className={cn(
+          {createElement(typeIcon, {
+            className: cn(
               "size-3.5 shrink-0",
               isUnseen ? "text-foreground" : "text-muted-foreground",
-            )}
-          />
+            ),
+          })}
           <Small
             className={cn(
               "truncate",
diff --git a/js/desktop/src/features/particles/stream-members-overlay.tsx b/js/desktop/src/features/particles/stream-members-overlay.tsx
index 999c5f1..9a42de6 100644
--- a/js/desktop/src/features/particles/stream-members-overlay.tsx
+++ b/js/desktop/src/features/particles/stream-members-overlay.tsx
@@ -34,7 +34,10 @@ export function StreamMembersOverlay({
   const network = useNetwork(networkId);
   const humans = network?.humans ?? [];
   const creatorId = streamParticle.created_by_human_id;
-  const visibility = parseVisibleTo(streamParticle.visible_to, networkId);
+  const visibility = useMemo(
+    () => parseVisibleTo(streamParticle.visible_to, networkId),
+    [streamParticle.visible_to, networkId],
+  );
 
   const docPath = useMemo(
     () => toFirestoreDocPath(particlePath(networkId, [streamParticle.id])),
diff --git a/js/desktop/src/features/particles/stream-view.tsx b/js/desktop/src/features/particles/stream-view.tsx
index af079ba..8600dfe 100644
--- a/js/desktop/src/features/particles/stream-view.tsx
+++ b/js/desktop/src/features/particles/stream-view.tsx
@@ -51,24 +51,26 @@ function useExitCountdown(
   disabled: boolean,
   onExit: () => void,
 ) {
-  const [remainingMs, setRemainingMs] = useState<number | null>(null);
+  const [remainingMs, setRemainingMs] = useState<number | null>(
+    status === "ended" ? EXIT_DELAY_MS : null,
+  );
+  const [prevStatus, setPrevStatus] = useState(status);
 
   const handleExit = useEffectEvent(() => {
     onExit();
   });
 
-  // Start/cancel countdown based on playback status
-  useEffect(() => {
-    if (status === "ended") {
-      setRemainingMs(EXIT_DELAY_MS);
-    } else {
-      setRemainingMs(null);
-    }
-  }, [status]);
+  // Start the countdown when playback ends; cancel it otherwise.
+  if (status !== prevStatus) {
+    setPrevStatus(status);
+    setRemainingMs(status === "ended" ? EXIT_DELAY_MS : null);
+  }
+
+  const isCountingDown = remainingMs !== null && remainingMs > 0;
 
   // Tick the countdown down (pauses when compose is active)
   useEffect(() => {
-    if (remainingMs === null || remainingMs <= 0 || disabled) return;
+    if (!isCountingDown || disabled) return;
 
     const interval = setInterval(() => {
       setRemainingMs((prev) => {
@@ -79,7 +81,7 @@ function useExitCountdown(
     }, EXIT_TICK_MS);
 
     return () => clearInterval(interval);
-  }, [remainingMs !== null && remainingMs > 0, disabled]);
+  }, [isCountingDown, disabled]);
 
   // Navigate once countdown hits zero
   useEffect(() => {
@@ -197,12 +199,13 @@ function StreamViewInner({ path, streamParticle }: StreamViewProps) {
 
     const reactions = getReactions(currentParticle);
     toggleParticleReaction(currentParticleDocPath, emoji, authedUser.id, reactions);
-  }, [authedUser, currentParticle]);
+  }, [authedUser, currentParticle, networkId, streamParticle.id]);
 
   const [composeActive, setComposeActive] = useState(false);
   const [composeStep, setComposeStep] = useState<ComposeStep>("idle");
   const paused = usePlaybackPauseStore(selectIsPaused);
   const [progress, setProgress] = useState(0);
+  const [prevParticleId, setPrevParticleId] = useState(currentParticle?.id);
   const [showKeybindings, setShowKeybindings] = useState(false);
   const [textReactionOpen, setTextReactionOpen] = useState(false);
 
@@ -286,10 +289,11 @@ function StreamViewInner({ path, streamParticle }: StreamViewProps) {
     handleExitNavigate,
   );
 
-  // Reset progress when particle changes
-  useEffect(() => {
+  // Reset progress when the particle changes.
+  if (currentParticle?.id !== prevParticleId) {
+    setPrevParticleId(currentParticle?.id);
     setProgress(0);
-  }, [currentParticle?.id]);
+  }
 
   const handleParticleCreated = useCallback((particleId: string) => {
     if (currentIndex === -1) return;
diff --git a/js/desktop/src/features/particles/text-reaction-input.tsx b/js/desktop/src/features/particles/text-reaction-input.tsx
index 9820064..8237263 100644
--- a/js/desktop/src/features/particles/text-reaction-input.tsx
+++ b/js/desktop/src/features/particles/text-reaction-input.tsx
@@ -14,13 +14,19 @@ interface TextReactionInputProps {
 
 export function TextReactionInput({ open, onSubmit, onClose }: TextReactionInputProps) {
   const [value, setValue] = useState("");
+  const [prevOpen, setPrevOpen] = useState(open);
   const inputRef = useRef<HTMLInputElement>(null);
 
   useSuspendPlayback(open, "text-reaction");
 
+  // Clear the input each time the popup opens.
+  if (open !== prevOpen) {
+    setPrevOpen(open);
+    if (open) setValue("");
+  }
+
   useEffect(() => {
     if (!open) return;
-    setValue("");
     const id = requestAnimationFrame(() => inputRef.current?.focus());
     return () => cancelAnimationFrame(id);
   }, [open]);
diff --git a/js/desktop/src/features/particles/transcript-overlay.tsx b/js/desktop/src/features/particles/transcript-overlay.tsx
index e18a1fc..5c68d2c 100644
--- a/js/desktop/src/features/particles/transcript-overlay.tsx
+++ b/js/desktop/src/features/particles/transcript-overlay.tsx
@@ -1,4 +1,4 @@
-import { useMemo, useRef } from "react";
+import { useMemo, useState } from "react";
 import type { Transcript } from "@/api/types";
 
 type Sentence = Transcript["paragraphs"][number]["sentences"][number];
@@ -41,35 +41,40 @@ export function TranscriptOverlay({
   const activeWord =
     activeWordIndex !== null ? transcript.words[activeWordIndex] : null;
 
-  // Remember the last spoken word so highlights hold during pauses
-  const lastSpokenWordRef = useRef<Word | null>(null);
-  if (activeWord) {
-    lastSpokenWordRef.current = activeWord;
+  // Remember the last spoken word so highlights hold during pauses.
+  const [lastSpokenWord, setLastSpokenWord] = useState<Word | null>(null);
+  if (activeWord && activeWord !== lastSpokenWord) {
+    setLastSpokenWord(activeWord);
   }
-  const highlightWord = activeWord ?? lastSpokenWordRef.current;
+  const highlightWord = activeWord ?? lastSpokenWord;
 
-  const lastChunkRef = useRef<Word[] | null>(null);
-
-  // Find which chunk contains the active word, holding the last one during pauses
-  const activeChunk = useMemo(() => {
-    if (activeWord) {
-      for (const chunk of chunks) {
-        if (chunk.some((w) => w.start === activeWord.start && w.end === activeWord.end)) {
-          lastChunkRef.current = chunk;
-          return chunk;
-        }
-      }
-    }
-    // No active word (speaker pausing) — hold the last chunk
-    if (lastChunkRef.current && chunks.some((c) => c === lastChunkRef.current)) {
-      return lastChunkRef.current;
-    }
-    // Sentence changed, last chunk no longer valid — use first chunk
-    const fallback = chunks[0] ?? null;
-    lastChunkRef.current = fallback;
-    return fallback;
+  // The chunk currently being spoken (null during a pause or if not found).
+  const spokenChunk = useMemo(() => {
+    if (!activeWord) return null;
+    return (
+      chunks.find((chunk) =>
+        chunk.some(
+          (w) => w.start === activeWord.start && w.end === activeWord.end,
+        ),
+      ) ?? null
+    );
   }, [chunks, activeWord]);
 
+  // Resolve which chunk to display: the spoken one, else hold the last one while
+  // it's still part of the current sentence, else fall back to the first chunk.
+  const [lastChunk, setLastChunk] = useState<Word[] | null>(null);
+  let activeChunk: Word[] | null;
+  if (spokenChunk) {
+    activeChunk = spokenChunk;
+  } else if (lastChunk && chunks.includes(lastChunk)) {
+    activeChunk = lastChunk;
+  } else {
+    activeChunk = chunks[0] ?? null;
+  }
+  if (activeChunk !== lastChunk) {
+    setLastChunk(activeChunk);
+  }
+
   if (!activeSentence || !activeChunk || activeChunk.length === 0) return null;
 
   return (
diff --git a/js/desktop/src/features/settings/audio-video-settings-page.tsx b/js/desktop/src/features/settings/audio-video-settings-page.tsx
index 644d850..26eec44 100644
--- a/js/desktop/src/features/settings/audio-video-settings-page.tsx
+++ b/js/desktop/src/features/settings/audio-video-settings-page.tsx
@@ -34,12 +34,20 @@ function usePreviewStream(
 ): { stream: MediaStream | null; error: string | null } {
   const [stream, setStream] = useState<MediaStream | null>(null);
   const [error, setError] = useState<string | null>(null);
+  const [prevEnabled, setPrevEnabled] = useState(enabled);
 
-  useEffect(() => {
+  // Clear the preview when disabled; the effect below only manages the
+  // getUserMedia subscription.
+  if (enabled !== prevEnabled) {
+    setPrevEnabled(enabled);
     if (!enabled) {
       setStream(null);
-      return;
+      setError(null);
     }
+  }
+
+  useEffect(() => {
+    if (!enabled) return;
 
     let cancelled = false;
     let active: MediaStream | null = null;
diff --git a/js/desktop/src/hooks/use-channel.ts b/js/desktop/src/hooks/use-channel.ts
index 0641647..1712f25 100644
--- a/js/desktop/src/hooks/use-channel.ts
+++ b/js/desktop/src/hooks/use-channel.ts
@@ -23,11 +23,7 @@ export function useChannel(channelId: string | null): UseChannelResult {
   const [messages, setMessages] = useState<ChannelMessage[]>([]);
 
   useEffect(() => {
-    if (!client || !channelId) {
-      setPresence([]);
-      setMessages([]);
-      return;
-    }
+    if (!client || !channelId) return;
 
     client.subscribe(channelId);
 
@@ -66,6 +62,9 @@ export function useChannel(channelId: string | null): UseChannelResult {
       client.off(channelId, "leave", onLeave);
       client.off(channelId, "message", onMessage);
       client.unsubscribe(channelId);
+      // Clear on teardown so a new channel doesn't briefly show stale data.
+      setPresence([]);
+      setMessages([]);
     };
   }, [client, channelId]);
 
diff --git a/js/desktop/src/hooks/use-file-input.ts b/js/desktop/src/hooks/use-file-input.ts
index cf816cd..f7c9486 100644
--- a/js/desktop/src/hooks/use-file-input.ts
+++ b/js/desktop/src/hooks/use-file-input.ts
@@ -10,9 +10,12 @@ export function useFileInput({ onFilesSelected, enabled }: UseFileInputOptions)
   const inputRef = useRef<HTMLInputElement | null>(null);
   const dragCountRef = useRef(0);
 
-  // Stable ref for the callback to avoid re-registering effects
+  // Latest callback in a ref, so the effects below don't re-register when the
+  // caller passes a new function each render.
   const onFilesRef = useRef(onFilesSelected);
-  onFilesRef.current = onFilesSelected;
+  useEffect(() => {
+    onFilesRef.current = onFilesSelected;
+  }, [onFilesSelected]);
 
   // Hidden file input element
   useEffect(() => {
diff --git a/js/desktop/src/hooks/use-media-devices.ts b/js/desktop/src/hooks/use-media-devices.ts
index a0641bb..c6b71cf 100644
--- a/js/desktop/src/hooks/use-media-devices.ts
+++ b/js/desktop/src/hooks/use-media-devices.ts
@@ -25,21 +25,23 @@ export function useMediaDevices(): UseMediaDevicesResult {
     useState<PermissionState>("unknown");
   const [error, setError] = useState<string | null>(null);
 
-  const refresh = useCallback(async () => {
-    try {
-      const list = await navigator.mediaDevices.enumerateDevices();
-      setDevices(list);
-      // If at least one input device has a non-empty label, permission
-      // has been granted at some point for that device kind.
-      const hasLabels = list.some(
-        (d) =>
-          (d.kind === "audioinput" || d.kind === "videoinput") &&
-          d.label.length > 0,
-      );
-      if (hasLabels) setPermissionState("granted");
-    } catch (err) {
-      setError(err instanceof Error ? err.message : "Failed to list devices");
-    }
+  const refresh = useCallback(() => {
+    return navigator.mediaDevices
+      .enumerateDevices()
+      .then((list) => {
+        setDevices(list);
+        // If at least one input device has a non-empty label, permission
+        // has been granted at some point for that device kind.
+        const hasLabels = list.some(
+          (d) =>
+            (d.kind === "audioinput" || d.kind === "videoinput") &&
+            d.label.length > 0,
+        );
+        if (hasLabels) setPermissionState("granted");
+      })
+      .catch((err) => {
+        setError(err instanceof Error ? err.message : "Failed to list devices");
+      });
   }, []);
 
   const requestLabels = useCallback(async () => {
diff --git a/js/desktop/src/hooks/use-object-url.ts b/js/desktop/src/hooks/use-object-url.ts
new file mode 100644
index 0000000..df22575
--- /dev/null
+++ b/js/desktop/src/hooks/use-object-url.ts
@@ -0,0 +1,28 @@
+import { useEffect, useState } from "react";
+
+/**
+ * Creates an object URL for a Blob/File and revokes it when the source changes
+ * or the component unmounts. Returns null when given null.
+ *
+ * `createObjectURL` is an imperative side effect that must run inside an effect,
+ * so publishing the resulting URL to state here is genuine external-resource
+ * synchronization rather than a render cascade — hence the single, contained
+ * lint suppression below.
+ */
+export function useObjectUrl(source: Blob | null): string | null {
+  const [url, setUrl] = useState<string | null>(null);
+
+  useEffect(() => {
+    if (!source) return;
+    const objectUrl = URL.createObjectURL(source);
+    // Intended external-resource publish (see hook doc), not a render cascade.
+    // eslint-disable-next-line react-hooks/set-state-in-effect
+    setUrl(objectUrl);
+    return () => {
+      URL.revokeObjectURL(objectUrl);
+      setUrl(null); // in cleanup, not the effect body — so no suppression needed
+    };
+  }, [source]);
+
+  return source ? url : null;
+}
diff --git a/js/desktop/src/hooks/use-particle.ts b/js/desktop/src/hooks/use-particle.ts
index 6eafd20..50c4181 100644
--- a/js/desktop/src/hooks/use-particle.ts
+++ b/js/desktop/src/hooks/use-particle.ts
@@ -1,4 +1,4 @@
-import { useState, useEffect } from "react";
+import { useState, useEffect, useRef } from "react";
 import {
   subscribeToParticle,
   subscribeToParticleChildren,
@@ -27,10 +27,6 @@ export function useLiveParticle(path: ParticlePath): UseLiveParticleResult {
   const [error, setError] = useState<Error | null>(null);
 
   useEffect(() => {
-    setIsLoading(true);
-    setError(null);
-    setParticle(null);
-
     const docPath = toFirestoreDocPath(path);
     const unsubscribe = subscribeToParticle(
       docPath,
@@ -44,7 +40,13 @@ export function useLiveParticle(path: ParticlePath): UseLiveParticleResult {
       },
     );
 
-    return unsubscribe;
+    return () => {
+      unsubscribe();
+      // Reset on teardown so a new path doesn't flash the previous particle.
+      setIsLoading(true);
+      setError(null);
+      setParticle(null);
+    };
   }, [path]);
 
   return { particle, isLoading, error };
@@ -83,16 +85,17 @@ export function useLiveParticleChildren(
   const [isLoading, setIsLoading] = useState(true);
   const [error, setError] = useState<Error | null>(null);
 
+  // Keep the latest add/remove callbacks in refs so changing them doesn't force
+  // the subscription to re-attach — they're notifications, not query params.
+  const onAddedRef = useRef(onAdded);
+  const onRemovedRef = useRef(onRemoved);
   useEffect(() => {
-    if (!path) {
-      setChildren([]);
-      setIsLoading(false);
-      return;
-    }
+    onAddedRef.current = onAdded;
+    onRemovedRef.current = onRemoved;
+  }, [onAdded, onRemoved]);
 
-    setIsLoading(true);
-    setError(null);
-    setChildren([]);
+  useEffect(() => {
+    if (!path) return;
 
     const collectionPath = toFirestoreChildrenPath(path);
 
@@ -111,15 +114,27 @@ export function useLiveParticleChildren(
         visibilityScopes,
         orderByField,
         orderDirection,
-        onAdded,
-        onRemoved,
+        onAdded: (child: Particle) => onAddedRef.current?.(child),
+        onRemoved: (child: Particle, updatedChildren: Particle[]) =>
+          onRemovedRef.current?.(child, updatedChildren),
         whereFilter,
         limit,
       }
     );
 
-    return unsubscribe;
-  }, [path, whereFilter, limit]);
+    return () => {
+      unsubscribe();
+      // Reset on teardown so a new path doesn't flash the previous children.
+      setChildren([]);
+      setError(null);
+      setIsLoading(true);
+    };
+  }, [path, whereFilter, limit, orderByField, orderDirection, visibilityScopes]);
+
+  // No path: nothing to load, so report an empty non-loading state.
+  if (!path) {
+    return { children: [], isLoading: false, error: null };
+  }
 
   return { children, isLoading, error };
 }
@@ -134,9 +149,6 @@ export function useLiveLatestChild(path: ParticlePath): UseLiveLatestChildResult
   const [isLoading, setIsLoading] = useState(true);
 
   useEffect(() => {
-    setIsLoading(true);
-    setLatestChild(null);
-
     const unsubscribe = subscribeToLatestChild(
       toFirestoreChildrenPath(path),
       (data) => {
@@ -148,7 +160,12 @@ export function useLiveLatestChild(path: ParticlePath): UseLiveLatestChildResult
       },
     );
 
-    return unsubscribe;
+    return () => {
+      unsubscribe();
+      // Reset on teardown so a new path doesn't flash the previous child.
+      setIsLoading(true);
+      setLatestChild(null);
+    };
   }, [path]);
 
   return { latestChild, isLoading };
diff --git a/js/desktop/src/hooks/use-stream-keyboard-nav.ts b/js/desktop/src/hooks/use-stream-keyboard-nav.ts
index ad2c09d..28a0490 100644
--- a/js/desktop/src/hooks/use-stream-keyboard-nav.ts
+++ b/js/desktop/src/hooks/use-stream-keyboard-nav.ts
@@ -12,19 +12,23 @@ export function useStreamKeyboardNav({
   enabled,
   onNavigate,
 }: UseStreamKeyboardNavOptions) {
-  const [selectedIndex, setSelectedIndex] = useState<number | null>(null);
+  const [selectedIndex, setSelectedIndex] = useState<number | null>(
+    streams.length > 0 ? 0 : null,
+  );
+  const [prevStreamCount, setPrevStreamCount] = useState(streams.length);
   const recordingMode = useMediaSettingsStore((s) => s.recordingMode);
   const setRecordingMode = useMediaSettingsStore((s) => s.setRecordingMode);
 
-  // Initialize selection when streams first load; clear if streams become empty.
-  // Do NOT reset on every Firestore update — that would scroll the list to the top.
-  useEffect(() => {
-    setSelectedIndex((prev) => {
-      if (streams.length === 0) return null;
-      if (prev === null) return 0;
-      return prev;
-    });
-  }, [streams.length]);
+  // Select the first stream once they load and clear when empty — but not on
+  // every Firestore update, which would scroll the list back to the top.
+  if (streams.length !== prevStreamCount) {
+    setPrevStreamCount(streams.length);
+    if (streams.length === 0) {
+      setSelectedIndex(null);
+    } else if (selectedIndex === null) {
+      setSelectedIndex(0);
+    }
+  }
 
   useEffect(() => {
     if (!enabled || streams.length === 0) return;
diff --git a/js/desktop/src/hooks/use-stream-particles.ts b/js/desktop/src/hooks/use-stream-particles.ts
index 373f63a..a44de72 100644
--- a/js/desktop/src/hooks/use-stream-particles.ts
+++ b/js/desktop/src/hooks/use-stream-particles.ts
@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useMemo, useState } from "react";
+import { useCallback, useMemo, useState } from "react";
 import { where, type QueryFieldFilterConstraint } from "firebase/firestore";
 import { useLiveParticleChildren } from "@/hooks/use-particle";
 import { useAuthStore } from "@/stores/auth-store";
@@ -52,14 +52,16 @@ export function useStreamParticles(
   const visibilityScopes = useVisibilityScopes(user?.id, networkId);
 
   const [closedLimit, setClosedLimit] = useState(CLOSED_INITIAL_PAGE_SIZE);
+  const [prevStatus, setPrevStatus] = useState(status);
 
-  // Every time the user switches back to the closed tab, start with a fresh
-  // window. Avoids an ever-growing subscription across a long session.
-  useEffect(() => {
+  // Switching back to the closed tab starts a fresh window, avoiding an
+  // ever-growing subscription across a long session.
+  if (status !== prevStatus) {
+    setPrevStatus(status);
     if (status === "closed") {
       setClosedLimit(CLOSED_INITIAL_PAGE_SIZE);
     }
-  }, [status]);
+  }
 
   const whereFilter: QueryFieldFilterConstraint =
     status === "open" ? OPEN_STATUS_FILTER : CLOSED_STATUS_FILTER;
diff --git a/js/desktop/src/hooks/use-stream-playback.ts b/js/desktop/src/hooks/use-stream-playback.ts
index 24d7435..46703fa 100644
--- a/js/desktop/src/hooks/use-stream-playback.ts
+++ b/js/desktop/src/hooks/use-stream-playback.ts
@@ -84,21 +84,25 @@ export function useStreamPlayback(
   const [state, dispatch] = useReducer(playbackReducer, initialState);
   // Track the stream ID we've initialized for, to reset when navigating between streams
   const initializedForRef = useRef<string | null>(null);
+  // Latest currentIndex for onParticleRemoved (passed to the subscription), so
+  // it reads the current value without re-subscribing. useEffectEvent can't be
+  // used — it may not be passed to another hook.
+  const currentIndexRef = useRef(0);
 
   // --- Firestore change callbacks ---
   const onParticleAdded = useCallback((particle: Particle) => {
     dispatch({ type: "PARTICLE_ADDED", particleId: particle.id });
   }, []);
 
-  const onParticleRemoved = useEffectEvent((removed: Particle, updatedChildren: Particle[]) => {
-    const fallbackIndex = Math.min(currentIndex, updatedChildren.length - 1);
+  const onParticleRemoved = useCallback((removed: Particle, updatedChildren: Particle[]) => {
+    const fallbackIndex = Math.min(currentIndexRef.current, updatedChildren.length - 1);
     const fallback = updatedChildren[Math.max(0, fallbackIndex)];
     dispatch({
       type: "PARTICLE_REMOVED",
       removedParticleId: removed.id,
       fallbackParticleId: fallback?.id ?? null,
     });
-  });
+  }, []);
 
   const { children } = useLiveParticleChildren(
     path,
@@ -118,6 +122,11 @@ export function useStreamPlayback(
 
   const currentParticle = currentIndex !== -1 ? children[currentIndex] : null;
 
+  // Keep the latest-index ref in sync for onParticleRemoved (above).
+  useEffect(() => {
+    currentIndexRef.current = currentIndex;
+  }, [currentIndex]);
+
   // Fallback init — always sees latest children/state via useEffectEvent
   const initFallback = useEffectEvent(() => {
     if (state.initialized || children.length === 0) return;
diff --git a/js/desktop/src/lib/sound-effects/engine.ts b/js/desktop/src/lib/sound-effects/engine.ts
index faf9700..65c9d2d 100644
--- a/js/desktop/src/lib/sound-effects/engine.ts
+++ b/js/desktop/src/lib/sound-effects/engine.ts
@@ -79,7 +79,7 @@ class SoundEffectsEngine {
    */
   preload(name: string, url: string): Promise<AudioBuffer | null> {
     if (this.buffers.has(name)) {
-      return Promise.resolve(this.buffers.get(name));
+      return Promise.resolve(this.buffers.get(name) ?? null);
     }
     const existing = this.loading.get(name);
     if (existing) return existing;