Show image previews in optimistic user messages

packages/app/src/utils/pending-create-images.ts

@@ -0,0 +1,39 @@
+import type { StreamItem, UserMessageImageAttachment } from "@/types/stream";
+
+type MergePendingCreateImagesParams = {
+  streamItems: StreamItem[];
+  messageId: string;
+  text: string;
+  images?: UserMessageImageAttachment[];
+};
+
+export function mergePendingCreateImages({
+  streamItems,
+  messageId,
+  text,
+  images,
+}: MergePendingCreateImagesParams): StreamItem[] {
+  if (!images || images.length === 0) {
+    return streamItems;
+  }
+
+  const targetIndex = streamItems.findIndex(
+    (item) =>
+      item.kind === "user_message" && (item.id === messageId || item.text === text)
+  );
+  if (targetIndex < 0) {
+    return streamItems;
+  }
+
+  const target = streamItems[targetIndex];
+  if (target.kind !== "user_message") {
+    return streamItems;
+  }
+  if (target.images && target.images.length > 0) {
+    return streamItems;
+  }
+
+  const next = [...streamItems];
+  next[targetIndex] = { ...target, images };
+  return next;
+}