fix(chat): snap to bottom after send to mask composer-shrink layout shift

apps/desktop/src/pages/ConversationPage.tsx

@@ -754,6 +754,24 @@ export function ConversationPage() {
     lastPendingCountRef.current = pending.length;
   }, [pending.length]);
 
+  // Snap the viewport back to the bottom after a send. The composer
+  // shrinks (cleared text, dismissed reply preview, dropped attachment
+  // thumbs) which lets the Virtuoso area grow vertically — leaving the
+  // just-sent bubble visibly above the new bottom for a frame.
+  // `requestAnimationFrame` defers the scroll until React has committed
+  // the composer-height change, so Virtuoso's ResizeObserver has
+  // already seen the new viewport and `index: 'LAST', align: 'end'`
+  // targets the correct bottom edge.
+  const snapToBottom = useCallback(() => {
+    window.requestAnimationFrame(() => {
+      virtuosoRef.current?.scrollToIndex({
+        index: 'LAST',
+        align: 'end',
+        behavior: 'auto',
+      });
+    });
+  }, []);
+
   async function handleSend(e?: React.FormEvent) {
     e?.preventDefault();
     if ((!text.trim() && attachments.length === 0) || sending) return;
@@ -773,6 +791,7 @@ export function ConversationPage() {
       setStickToBottom(true);
       notifyStopTyping();
       if (id) clearDraft(id);
+      snapToBottom();
     } catch (err: unknown) {
       const code = extractErrorCode(err);
       setSendError(
@@ -798,13 +817,14 @@ export function ConversationPage() {
         setReplyTo(null);
         setStickToBottom(true);
         notifyStopTyping();
+        snapToBottom();
       } catch (err: unknown) {
         setPollError(err instanceof Error ? err.message : 'Umfrage konnte nicht gesendet werden');
       } finally {
         setPollSending(false);
       }
     },
-    [send, replyTo?.id, notifyStopTyping],
+    [send, replyTo?.id, notifyStopTyping, snapToBottom],
   );
 
   const handleCreateWhiteboard = useCallback(async () => {
@@ -817,12 +837,13 @@ export function ConversationPage() {
       setReplyTo(null);
       setStickToBottom(true);
       setOpenWhiteboardId(board.id);
+      snapToBottom();
     } catch (err: unknown) {
       setSendError(err instanceof Error ? err.message : 'Whiteboard konnte nicht angelegt werden');
     } finally {
       setCreatingWhiteboard(false);
     }
-  }, [id, creatingWhiteboard, send, replyTo?.id]);
+  }, [id, creatingWhiteboard, send, replyTo?.id, snapToBottom]);
 
   const handleStartWatchTogether = useCallback(async () => {
     if (!id) return;
@@ -842,12 +863,13 @@ export function ConversationPage() {
       setWatchDialogOpen(false);
       setWatchUrl('');
       setOpenWatchSessionId(ws.id);
+      snapToBottom();
     } catch (err: unknown) {
       setWatchError(err instanceof Error ? err.message : 'Konnte Watch-Together nicht starten');
     } finally {
       setWatchCreating(false);
     }
-  }, [id, watchUrl, send, replyTo?.id]);
+  }, [id, watchUrl, send, replyTo?.id, snapToBottom]);
 
   const handleStartGame = useCallback(async (gameType: GameType) => {
     if (!id) return;
@@ -874,12 +896,13 @@ export function ConversationPage() {
       setStickToBottom(true);
       setGameDialogOpen(false);
       setOpenGameId(game.id);
+      snapToBottom();
     } catch (err: unknown) {
       setGameError(err instanceof Error ? err.message : 'Konnte Spiel nicht starten');
     } finally {
       setGameCreating(false);
     }
-  }, [id, conversation, myId, send, replyTo?.id]);
+  }, [id, conversation, myId, send, replyTo?.id, snapToBottom]);
 
   async function ingestFiles(files: File[]) {
     const compressed = await compressImages(files);