diff --git a/js/src/components/composing-indicator.tsx b/js/src/components/composing-indicator.tsx
new file mode 100644
index 0000000..8c22b51
--- /dev/null
+++ b/js/src/components/composing-indicator.tsx
@@ -0,0 +1,47 @@
+import type { Human } from "@/api/types";
+import type { ComposingUser } from "@/features/particles/stream-presence-context";
+
+interface ComposingIndicatorProps {
+  users: ComposingUser[];
+  networkHumans?: Human[];
+}
+
+/**
+ * Composing indicators pinned to the left edge, text running bottom-to-top
+ * via writing-mode so it hugs the edge without transform math issues.
+ */
+export function ComposingIndicator({
+  users,
+  networkHumans,
+}: ComposingIndicatorProps) {
+  if (users.length === 0) return null;
+
+  return (
+    <div
+      className="z-100 absolute left-2 top-1/2 z-20 flex -translate-y-1/2 flex-col gap-1.5 animate-in fade-in duration-200"
+      style={{ writingMode: "vertical-rl" }}
+    >
+      {users.map((u) => {
+        const human = networkHumans?.find((h) => h.id === u.humanId);
+        const name = human?.email_prefix ?? u.humanId;
+        const modeLabel = u.mode === "typing" ? "typing" : "recording";
+
+        return (
+          <div
+            key={u.humanId}
+            className="flex rotate-180 items-center gap-1.5 rounded-full bg-white/10 px-2 py-1 backdrop-blur-sm"
+          >
+            <span className="flex gap-0.5">
+              <span className="size-1 rounded-full bg-white/70 animate-bounce [animation-delay:0ms]" />
+              <span className="size-1 rounded-full bg-white/70 animate-bounce [animation-delay:150ms]" />
+              <span className="size-1 rounded-full bg-white/70 animate-bounce [animation-delay:300ms]" />
+            </span>
+            <span className="whitespace-nowrap text-[10px] text-white/50">
+              {name} {modeLabel}
+            </span>
+          </div>
+        );
+      })}
+    </div>
+  );
+}
diff --git a/js/src/features/compose/compose-overlay.tsx b/js/src/features/compose/compose-overlay.tsx
index f2cb065..018affc 100644
--- a/js/src/features/compose/compose-overlay.tsx
+++ b/js/src/features/compose/compose-overlay.tsx
@@ -17,7 +17,7 @@ import { createImageThumbnail } from "@/lib/image-thumbnail";
 import { MAX_ATTACHMENT_SIZE_BYTES, MAX_ATTACHMENTS } from "@/lib/constants";
 import type { PendingAttachment } from "@/features/compose/attachment-strip";
 
-type ComposeStep = "idle" | "picking" | "recording" | "reviewing" | "typing" | "configuring" | "submitting";
+export type ComposeStep = "idle" | "picking" | "recording" | "reviewing" | "typing" | "configuring" | "submitting";
 
 type RecordingSource = "media" | "screen";
 
@@ -26,6 +26,7 @@ interface ComposeOverlayProps {
   // Optional target path for reply mode. If not provided, compose creates a new stream.
   targetPath?: ParticlePath;
   onActiveChange?: (active: boolean) => void;
+  onStepChange?: (step: ComposeStep) => void;
   onParticleCreated?: (particleId: string) => void;
   /** When true, composing is blocked (e.g. stream is closed). */
   disabled?: boolean;
@@ -42,6 +43,7 @@ export function ComposeOverlay({
   networkId,
   targetPath,
   onActiveChange,
+  onStepChange,
   onParticleCreated,
   disabled,
 }: ComposeOverlayProps) {
@@ -77,7 +79,8 @@ export function ComposeOverlay({
   // Notify parent when active state changes
   useEffect(() => {
     onActiveChange?.(step !== "idle");
-  }, [step, onActiveChange]);
+    onStepChange?.(step);
+  }, [step, onActiveChange, onStepChange]);
 
   const revokeAttachmentThumbnails = useCallback((items: PendingAttachment[]) => {
     for (const a of items) {
diff --git a/js/src/features/particles/playback-page-indicator.tsx b/js/src/features/particles/playback-page-indicator.tsx
index 10cfa27..d7d1bee 100644
--- a/js/src/features/particles/playback-page-indicator.tsx
+++ b/js/src/features/particles/playback-page-indicator.tsx
@@ -1,4 +1,4 @@
-import { Avatar, AvatarFallback } from "@/components/ui/avatar";
+import { Avatar, AvatarBadge, AvatarFallback } from "@/components/ui/avatar";
 import {
   Tooltip,
   TooltipContent,
@@ -14,6 +14,8 @@ interface PlaybackPageIndicatorProps {
   progress: number;
   onGoTo: (index: number) => void;
   presenceBySegment?: Map<number, HumanPresence[]>;
+  /** Set of humanIds currently online in the stream channel. */
+  onlineHumanIds?: Set<string>;
   /** Render only avatars or only tracks. Omit to render both. */
   layer?: "avatars" | "tracks";
 }
@@ -24,6 +26,7 @@ export function PlaybackPageIndicator({
   progress,
   onGoTo,
   presenceBySegment,
+  onlineHumanIds,
   layer,
 }: PlaybackPageIndicatorProps) {
   if (total === 0) return null;
@@ -38,7 +41,7 @@ export function PlaybackPageIndicator({
         return (
           <div key={i} className="flex flex-1 flex-col items-stretch">
             {showAvatars && presence && presence.length > 0 && (
-              <SegmentPresenceAvatars presence={presence} />
+              <SegmentPresenceAvatars presence={presence} onlineHumanIds={onlineHumanIds} />
             )}
             {showTracks && (
               <button
@@ -74,8 +77,10 @@ export function PlaybackPageIndicator({
 
 function SegmentPresenceAvatars({
   presence,
+  onlineHumanIds,
 }: {
   presence: HumanPresence[];
+  onlineHumanIds?: Set<string>;
 }) {
   const visible = presence.slice(0, MAX_VISIBLE_AVATARS);
   const overflow = presence.length - MAX_VISIBLE_AVATARS;
@@ -89,6 +94,9 @@ function SegmentPresenceAvatars({
               <AvatarFallback>
                 {human.emailPrefix.slice(0, 2).toUpperCase()}
               </AvatarFallback>
+              {onlineHumanIds?.has(human.humanId) && (
+                <AvatarBadge className="bg-green-500" />
+              )}
             </Avatar>
           </TooltipTrigger>
           <TooltipContent side="top" className="text-xs">
diff --git a/js/src/features/particles/stream-presence-context.tsx b/js/src/features/particles/stream-presence-context.tsx
new file mode 100644
index 0000000..ae8c5f3
--- /dev/null
+++ b/js/src/features/particles/stream-presence-context.tsx
@@ -0,0 +1,229 @@
+import {
+  createContext,
+  useCallback,
+  useContext,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+  type ReactNode,
+} from "react";
+import { useChannel } from "@/hooks/use-channel";
+import { useAuthStore } from "@/stores/auth-store";
+import type { ChannelMessage } from "@/lib/pusher-client";
+
+// ---------------------------------------------------------------------------
+// Types
+// ---------------------------------------------------------------------------
+
+export type ComposingMode = "recording" | "typing" | "screen";
+
+export interface ComposingUser {
+  humanId: string;
+  mode: ComposingMode;
+  lastSeen: number;
+}
+
+interface StreamPresenceContextValue {
+  onlineHumanIds: Set<string>;
+  composingUsers: ComposingUser[];
+  startComposing: (mode: ComposingMode) => void;
+  stopComposing: () => void;
+}
+
+// ---------------------------------------------------------------------------
+// Constants
+// ---------------------------------------------------------------------------
+
+const COMPOSING_TIMEOUT_MS = 10_000;
+const COMPOSING_HEARTBEAT_MS = 5_000;
+const COMPOSING_CLEANUP_INTERVAL_MS = 2_000;
+
+// ---------------------------------------------------------------------------
+// Context
+// ---------------------------------------------------------------------------
+
+const StreamPresenceContext = createContext<StreamPresenceContextValue | null>(
+  null,
+);
+
+// ---------------------------------------------------------------------------
+// Provider
+// ---------------------------------------------------------------------------
+
+interface StreamPresenceProviderProps {
+  networkId: string;
+  streamId: string;
+  children: ReactNode;
+}
+
+export function StreamPresenceProvider({
+  networkId,
+  streamId,
+  children,
+}: StreamPresenceProviderProps) {
+  const channelId = `stream:${networkId}:${streamId}`;
+  const { presence, messages, sendMessage } = useChannel(channelId);
+  const currentUserId = useAuthStore((s) => s.user?.id);
+
+  // --- Online presence ---
+  const onlineHumanIds = useMemo(() => new Set(presence), [presence]);
+
+  // --- Composing state ---
+  const [composingUsers, setComposingUsers] = useState<ComposingUser[]>([]);
+  const composingMapRef = useRef(new Map<string, ComposingUser>());
+  const processedCountRef = useRef(0);
+
+  // Process new messages incrementally
+  useEffect(() => {
+    if (messages.length <= processedCountRef.current) return;
+
+    const newMessages = messages.slice(processedCountRef.current);
+    processedCountRef.current = messages.length;
+
+    let changed = false;
+    const map = composingMapRef.current;
+
+    for (const msg of newMessages) {
+      const payload = msg.payload as
+        | { type: string; mode?: string }
+        | undefined;
+      if (!payload?.type) continue;
+
+      // Skip own events
+      if (msg.humanId === currentUserId) continue;
+
+      if (payload.type === "composing_start" && payload.mode) {
+        map.set(msg.humanId, {
+          humanId: msg.humanId,
+          mode: payload.mode as ComposingMode,
+          lastSeen: Date.now(),
+        });
+        changed = true;
+      } else if (payload.type === "composing_stop") {
+        if (map.delete(msg.humanId)) changed = true;
+      }
+    }
+
+    if (changed) {
+      setComposingUsers(Array.from(map.values()));
+    }
+  }, [messages, currentUserId]);
+
+  // Also clear composing when a user leaves the channel
+  useEffect(() => {
+    const map = composingMapRef.current;
+    const onlineSet = new Set(presence);
+    let changed = false;
+
+    for (const humanId of map.keys()) {
+      if (!onlineSet.has(humanId)) {
+        map.delete(humanId);
+        changed = true;
+      }
+    }
+
+    if (changed) {
+      setComposingUsers(Array.from(map.values()));
+    }
+  }, [presence]);
+
+  // Cleanup stale composing entries
+  useEffect(() => {
+    const interval = setInterval(() => {
+      const map = composingMapRef.current;
+      const now = Date.now();
+      let changed = false;
+
+      for (const [humanId, entry] of map) {
+        if (now - entry.lastSeen > COMPOSING_TIMEOUT_MS) {
+          map.delete(humanId);
+          changed = true;
+        }
+      }
+
+      if (changed) {
+        setComposingUsers(Array.from(map.values()));
+      }
+    }, COMPOSING_CLEANUP_INTERVAL_MS);
+
+    return () => clearInterval(interval);
+  }, []);
+
+  // --- Composing broadcast ---
+  const heartbeatRef = useRef<ReturnType<typeof setInterval>>(undefined);
+
+  const startComposing = useCallback(
+    (mode: ComposingMode) => {
+      // Send immediately
+      sendMessage({ type: "composing_start", mode });
+
+      // Clear any existing heartbeat
+      clearInterval(heartbeatRef.current);
+
+      // Start heartbeat
+      heartbeatRef.current = setInterval(() => {
+        sendMessage({ type: "composing_start", mode });
+      }, COMPOSING_HEARTBEAT_MS);
+    },
+    [sendMessage],
+  );
+
+  const stopComposing = useCallback(() => {
+    clearInterval(heartbeatRef.current);
+    heartbeatRef.current = undefined;
+    sendMessage({ type: "composing_stop" });
+  }, [sendMessage]);
+
+  // Cleanup heartbeat on unmount
+  useEffect(() => {
+    return () => {
+      clearInterval(heartbeatRef.current);
+    };
+  }, []);
+
+  const value = useMemo<StreamPresenceContextValue>(
+    () => ({
+      onlineHumanIds,
+      composingUsers,
+      startComposing,
+      stopComposing,
+    }),
+    [onlineHumanIds, composingUsers, startComposing, stopComposing],
+  );
+
+  return (
+    <StreamPresenceContext.Provider value={value}>
+      {children}
+    </StreamPresenceContext.Provider>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Hooks
+// ---------------------------------------------------------------------------
+
+function useStreamPresenceContext() {
+  const ctx = useContext(StreamPresenceContext);
+  if (!ctx) {
+    throw new Error(
+      "useStreamPresence must be used within a StreamPresenceProvider",
+    );
+  }
+  return ctx;
+}
+
+export function useStreamPresence() {
+  const { onlineHumanIds } = useStreamPresenceContext();
+  return { onlineHumanIds };
+}
+
+export function useStreamComposing() {
+  const { composingUsers } = useStreamPresenceContext();
+  return { composingUsers };
+}
+
+export function useStreamComposingBroadcast() {
+  const { startComposing, stopComposing } = useStreamPresenceContext();
+  return { startComposing, stopComposing };
+}
diff --git a/js/src/features/particles/stream-view.tsx b/js/src/features/particles/stream-view.tsx
index 02347cc..54f21c0 100644
--- a/js/src/features/particles/stream-view.tsx
+++ b/js/src/features/particles/stream-view.tsx
@@ -4,12 +4,12 @@ import { useAuthStore } from "@/stores/auth-store";
 import { apiClient } from "@/api/client";
 import { type Particle, REACTION_EMOJIS } from "@/api/types";
 import { parseParticlePath, particlePath, toFirestoreDocPath, type ParticlePath } from "@/lib/particle-path";
-import { ComposeOverlay } from "@/features/compose/compose-overlay";
+import { ComposeOverlay, type ComposeStep } from "@/features/compose/compose-overlay";
 import { PlaybackPageIndicator } from "@/features/particles/playback-page-indicator";
 import { MediaParticleView, type MediaParticleHandle } from "@/features/particles/media-particle-view";
 import { TextParticleView } from "@/features/particles/text-particle-view";
 import { FallbackParticleView } from "@/features/particles/fallback-particle-view";
-import { Avatar, AvatarFallback, AvatarGroup } from "@/components/ui/avatar";
+import { Avatar, AvatarBadge, AvatarFallback, AvatarGroup } from "@/components/ui/avatar";
 import { VideoAudioToggle } from "@/components/video-audio-toggle";
 import { useMediaSettingsStore } from "@/stores/media-settings-store";
 import { KeybindingsOverlay, type KeybindingGroup } from "@/components/keybindings-overlay";
@@ -31,6 +31,8 @@ import { RelativeTimestamp } from "@/components/relative-timestamp";
 import { useStreamPlayback } from "@/hooks/use-stream-playback";
 import { usePrefetchAdjacentMedia } from "@/hooks/use-prefetch-adjacent-media";
 import { usePresencePositions } from "@/hooks/use-presence-positions";
+import { StreamPresenceProvider, useStreamPresence, useStreamComposing, useStreamComposingBroadcast, type ComposingMode } from "@/features/particles/stream-presence-context";
+import { ComposingIndicator } from "@/components/composing-indicator";
 import { cn, getInitials } from "@/lib/utils";
 import { useMount } from "react-use";
 
@@ -153,6 +155,16 @@ interface StreamViewProps {
 
 export function StreamView({ path, streamParticle }: StreamViewProps) {
   const { networkId } = parseParticlePath(path);
+
+  return (
+    <StreamPresenceProvider networkId={networkId} streamId={streamParticle.id}>
+      <StreamViewInner path={path} streamParticle={streamParticle} />
+    </StreamPresenceProvider>
+  );
+}
+
+function StreamViewInner({ path, streamParticle }: StreamViewProps) {
+  const { networkId } = parseParticlePath(path);
   const navigate = useNavigate();
 
   useMount(() => {
@@ -185,6 +197,11 @@ export function StreamView({ path, streamParticle }: StreamViewProps) {
     authedUser?.id,
   );
 
+  // --- Stream presence (realtime via pusher) ---
+  const { onlineHumanIds } = useStreamPresence();
+  const { composingUsers } = useStreamComposing();
+  const { startComposing, stopComposing } = useStreamComposingBroadcast();
+
   const mediaRef = useRef<MediaParticleHandle>(null);
 
   const handleToggleReaction = useCallback((emoji: string) => {
@@ -201,10 +218,30 @@ export function StreamView({ path, streamParticle }: StreamViewProps) {
   }, [authedUser, currentParticle]);
 
   const [composeActive, setComposeActive] = useState(false);
+  const [composeStep, setComposeStep] = useState<ComposeStep>("idle");
   const [progress, setProgress] = useState(0);
   const [fastPlayback, setFastPlayback] = useState(false);
   const [showKeybindings, setShowKeybindings] = useState(false);
 
+  // Broadcast composing state to other viewers
+  useEffect(() => {
+    const stepToMode: Record<string, ComposingMode | null> = {
+      idle: null,
+      submitting: null,
+      recording: "recording",
+      typing: "typing",
+      reviewing: "typing",
+      configuring: "typing",
+      picking: "screen",
+    };
+    const mode = stepToMode[composeStep] ?? null;
+    if (mode) {
+      startComposing(mode);
+    } else {
+      stopComposing();
+    }
+  }, [composeStep, startComposing, stopComposing]);
+
   // Show/hide chrome on mouse activity (YouTube-style)
   const [showControls, setShowControls] = useState(true);
   const idleTimerRef = useRef<ReturnType<typeof setTimeout>>(undefined);
@@ -436,10 +473,14 @@ export function StreamView({ path, streamParticle }: StreamViewProps) {
         </div>
       )}
 
+      {/* Composing indicator — left edge, always visible */}
+      <ComposingIndicator users={composingUsers} networkHumans={network?.humans} />
+
       <ComposeOverlay
         networkId={networkId}
         targetPath={path}
         onActiveChange={setComposeActive}
+        onStepChange={setComposeStep}
         disabled={streamParticle.status === "closed"}
       />
 
@@ -454,6 +495,7 @@ export function StreamView({ path, streamParticle }: StreamViewProps) {
         progress={progress}
         onGoTo={goTo}
         presenceBySegment={presenceBySegment}
+        onlineHumanIds={onlineHumanIds}
         exitRemainingMs={exitRemainingMs}
         onOpenKeybindings={() => setShowKeybindings(true)}
       />
@@ -475,6 +517,7 @@ function BottomBar({
   progress,
   onGoTo,
   presenceBySegment,
+  onlineHumanIds,
   exitRemainingMs,
   onOpenKeybindings,
 }: {
@@ -484,6 +527,7 @@ function BottomBar({
   progress: number;
   onGoTo: (index: number) => void;
   presenceBySegment: Map<number, import("@/hooks/use-presence-positions").HumanPresence[]>;
+  onlineHumanIds: Set<string>;
   exitRemainingMs: number | null;
   onOpenKeybindings: () => void;
 }) {
@@ -499,6 +543,7 @@ function BottomBar({
         progress={progress}
         onGoTo={onGoTo}
         presenceBySegment={presenceBySegment}
+        onlineHumanIds={onlineHumanIds}
         layer="avatars"
       />
       {/* Blurred background container — tracks + controls */}
@@ -711,17 +756,19 @@ function NetworkBreadcrumbContent({ networkId }: { networkId: string }) {
 
 function ParticleBreadcrumbContent({ particle, networkId }: { particle: Particle; networkId: string }) {
   const network = useNetwork(networkId);
+  const { onlineHumanIds } = useStreamPresence();
   const creator = network?.humans?.find((h) => h.id === particle.created_by_human_id);
   const prefix = creator?.email_prefix ?? particle.created_by_human_id;
   const initials = prefix.slice(0, 2).toUpperCase();
+  const isOnline = particle.created_by_human_id ? onlineHumanIds.has(particle.created_by_human_id) : false;
 
   return (
-    <span className="flex
-        items-center gap-1.5">
+    <span className="flex items-center gap-1.5">
       <Avatar size="sm">
         <AvatarFallback>
           {initials}
         </AvatarFallback>
+        {isOnline && <AvatarBadge className="bg-green-500" />}
       </Avatar>
       {prefix} - <RelativeTimestamp date={particle.created_at} />
     </span>