feat: integrate Pi backend and Pi Web

pi-web/lib/draft-store.ts

@@ -0,0 +1,39 @@
+export interface ChatDraftImage {
+  data: string;
+  mimeType: string;
+}
+
+export interface ChatDraft {
+  value: string;
+  images: ChatDraftImage[];
+}
+
+const drafts = new Map<string, ChatDraft>();
+
+function cloneDraft(draft: ChatDraft): ChatDraft {
+  return {
+    value: draft.value,
+    images: draft.images.map((image) => ({ ...image })),
+  };
+}
+
+function isEmptyDraft(draft: ChatDraft): boolean {
+  return !draft.value && draft.images.length === 0;
+}
+
+export function getDraft(key: string): ChatDraft | null {
+  const draft = drafts.get(key);
+  return draft ? cloneDraft(draft) : null;
+}
+
+export function setDraft(key: string, draft: ChatDraft): void {
+  if (isEmptyDraft(draft)) {
+    drafts.delete(key);
+    return;
+  }
+  drafts.set(key, cloneDraft(draft));
+}
+
+export function clearDraft(key: string): void {
+  drafts.delete(key);
+}