js/mobile/src/features/compose/ComposeDock.tsx

@@ -56,6 +56,13 @@ interface ComposeDockProps {
   silentPresence?: boolean;
   submitMedia?: (params: SubmitMediaParams) => Promise<void>;
   submitText?: (content: string) => Promise<void>;
+  /**
+   * Called with the new particle's id right after it's created on the default
+   * send path. Not fired when `submitMedia`/`submitText` overrides are supplied,
+   * since those own the created particle themselves. Lets the stream follow a
+   * just-sent particle when the user was at the end.
+   */
+  onParticleCreated?: (particleId: string) => void;
 }
 
 export function ComposeDock({
@@ -64,6 +71,7 @@ export function ComposeDock({
   silentPresence = false,
   submitMedia,
   submitText: submitTextOverride,
+  onParticleCreated,
 }: ComposeDockProps) {
   const userId = useAuthStore((s) => s.user?.id);
 
@@ -147,7 +155,7 @@ export function ComposeDock({
           source: "camera",
         });
       } else {
-        await uploadMediaParticle({
+        const particleId = await uploadMediaParticle({
           networkId,
           targetPath,
           fileUri: captured.uri,
@@ -156,6 +164,7 @@ export function ComposeDock({
           source: "camera",
           createdByHumanId: userId,
         });
+        onParticleCreated?.(particleId);
       }
       void Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
       setUi({ kind: "idle" });
@@ -174,12 +183,13 @@ export function ComposeDock({
     if (submitTextOverride) {
       await submitTextOverride(content);
     } else {
-      await createTextParticle({
+      const particleId = await createTextParticle({
         networkId,
         targetPath,
         content,
         createdByHumanId: userId,
       });
+      onParticleCreated?.(particleId);
     }
     void Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
   });

js/mobile/src/features/stream-view/StreamView.tsx

@@ -105,8 +105,15 @@ function StreamViewInner({ streamParticle, path, onExit }: StreamViewProps) {
   const insets = useSafeAreaInsets();
   const { composingUsers } = useStreamComposing();
 
-  const { children, currentParticle, currentIndex, status, next, prev } =
-    useStreamPlayback(streamParticle, path);
+  const {
+    children,
+    currentParticle,
+    currentIndex,
+    status,
+    next,
+    prev,
+    goToParticle,
+  } = useStreamPlayback(streamParticle, path);
 
   const paused = usePlaybackPauseStore(selectIsPaused);
   const composing = usePlaybackPauseStore(selectIsComposing);
@@ -257,6 +264,22 @@ function StreamViewInner({ streamParticle, path, onExit }: StreamViewProps) {
 
   const openReactions = useCallback(() => setReactionsOpen(true), []);
 
+  // When the local user sends a particle while sitting on the last one, follow
+  // it forward so they stay caught up and the stream isn't left unseen. If they
+  // were browsing earlier particles, leave their position untouched. `children`
+  // is still the pre-send snapshot here (the live query hasn't delivered the new
+  // particle yet), so the last slot is children.length - 1; goToParticle resolves
+  // once it arrives. Mirrors desktop's StreamView.handleParticleCreated.
+  const handleParticleCreated = useCallback(
+    (particleId: string) => {
+      if (currentIndex === -1) return;
+      if (currentIndex === children.length - 1) {
+        goToParticle(particleId);
+      }
+    },
+    [children.length, currentIndex, goToParticle],
+  );
+
   // Reset progress whenever the active particle changes.
   useEffect(() => {
     setProgress(0);
@@ -642,7 +665,11 @@ function StreamViewInner({ streamParticle, path, onExit }: StreamViewProps) {
         {/* Compose dock + recording overlays. Sits above the GestureDetector
             so its hold-FAB pan gesture isn't competed-with by the StreamView
             tap zones. */}
-        <ComposeDock networkId={networkId} targetPath={path} />
+        <ComposeDock
+          networkId={networkId}
+          targetPath={path}
+          onParticleCreated={handleParticleCreated}
+        />
 
         {/* Reaction sheet — slides up over everything, suspends playback
             internally while open. */}