frontend/src/components/ParticipantSelector.tsx

@@ -41,11 +41,14 @@ export const ParticipantSelector = ({
   const addParticipant = useCallback((participant: Participant) => {
     onSelectionChange([...selectedParticipants, participant]);
     setSearchQuery('');
-    setHighlightedIndex(0);
-    setIsDropdownOpen(false);
-    // Re-focus input after selection
+    // Keep dropdown open for multi-select; clamp highlight to new list length
+    setHighlightedIndex((prev) => {
+      const newLength = filteredParticipants.length - 1;
+      return prev >= newLength ? Math.max(0, newLength - 1) : prev;
+    });
+    // Keep focus on input so user can continue selecting
     requestAnimationFrame(() => inputRef.current?.focus());
-  }, [onSelectionChange, selectedParticipants]);
+  }, [onSelectionChange, selectedParticipants, filteredParticipants.length]);
 
   const handleKeyDown = (e: React.KeyboardEvent) => {
     if (!isDropdownOpen || filteredParticipants.length === 0) return;