Add chat thread forking

web/src/lib/api.ts

@@ -1,6 +1,8 @@
 export type ChatSummary = {
   id: string;
   title: string | null;
+  parentChatId: string | null;
+  titleGenerationPending: boolean;
   createdAt: string;
   updatedAt: string;
   starred: boolean;
@@ -58,6 +60,8 @@ export type ToolCallEvent = {
 export type ChatDetail = {
   id: string;
   title: string | null;
+  parentChatId: string | null;
+  titleGenerationPending: boolean;
   createdAt: string;
   updatedAt: string;
   starred: boolean;
@@ -291,6 +295,14 @@ export async function getChat(chatId: string) {
   return data.chat;
 }
 
+export async function forkChat(chatId: string, messageId?: string) {
+  const data = await api<{ chat: ChatSummary }>(`/v1/chats/${chatId}/fork`, {
+    method: "POST",
+    body: JSON.stringify(messageId ? { messageId } : {}),
+  });
+  return data.chat;
+}
+
 export async function updateChatTitle(chatId: string, title: string) {
   const data = await api<{ chat: ChatSummary }>(`/v1/chats/${chatId}`, {
     method: "PATCH",

web/src/lib/chat-forking.ts

@@ -0,0 +1,82 @@
+export type ForkGroupingItem = {
+  kind: "chat" | "search";
+  id: string;
+  parentChatId: string | null;
+};
+
+type ChatTitleState = {
+  title: string | null;
+  titleGenerationPending: boolean;
+};
+
+type ForkPresentationItem = ForkGroupingItem & {
+  updatedAt: string;
+  starred: boolean;
+  starredAt: string | null;
+};
+
+export function groupForkedChatItems<T extends ForkGroupingItem>(items: T[]): T[][] {
+  const groups = new Map<string, { firstIndex: number; items: Array<{ item: T; index: number }> }>();
+
+  items.forEach((item, index) => {
+    const groupKey = item.kind === "chat" ? `chat:${item.parentChatId ?? item.id}` : `search:${item.id}`;
+    const group = groups.get(groupKey);
+    if (group) {
+      group.items.push({ item, index });
+      return;
+    }
+    groups.set(groupKey, { firstIndex: index, items: [{ item, index }] });
+  });
+
+  return [...groups.values()]
+    .sort((a, b) => a.firstIndex - b.firstIndex)
+    .map((group) =>
+      group.items
+        .sort((a, b) => {
+          const aIsRoot = a.item.kind === "chat" && a.item.parentChatId === null;
+          const bIsRoot = b.item.kind === "chat" && b.item.parentChatId === null;
+          if (aIsRoot !== bIsRoot) return aIsRoot ? -1 : 1;
+          return a.index - b.index;
+        })
+        .map(({ item }) => item)
+    );
+}
+
+export function filterSidebarItemsWithForkGroups<T extends ForkGroupingItem>(items: T[], matches: (item: T) => boolean): T[] {
+  return groupForkedChatItems(items)
+    .flatMap((group) => {
+      const matchingItems = group.filter(matches);
+      if (!matchingItems.length) return [];
+      const root = group.find((item) => item.kind === "chat" && item.parentChatId === null);
+      if (!root || matchingItems.includes(root)) return group;
+      return group.filter((item) => item === root || matchingItems.includes(item));
+    });
+}
+
+export function getForkGroupPresentation<T extends ForkPresentationItem>(groupItems: T[], allItems: T[]) {
+  const firstItem = groupItems[0];
+  if (!firstItem) return null;
+
+  const rootId = firstItem.kind === "chat" ? firstItem.parentChatId ?? firstItem.id : null;
+  const familyItems = rootId
+    ? allItems.filter((item) => item.kind === "chat" && (item.id === rootId || item.parentChatId === rootId))
+    : groupItems;
+  const updatedAt = familyItems.reduce(
+    (newest, item) => (new Date(item.updatedAt).getTime() > new Date(newest).getTime() ? item.updatedAt : newest),
+    firstItem.updatedAt
+  );
+  const starOwner = rootId
+    ? familyItems.find((item) => item.kind === "chat" && item.parentChatId === null)
+    : firstItem;
+
+  return {
+    updatedAt,
+    starred: starOwner?.starred ?? false,
+    starredAt: starOwner?.starredAt ?? null,
+  };
+}
+
+export function shouldRequestChatTitle(chat: ChatTitleState | null | undefined, isRequestInFlight: boolean) {
+  if (!chat || isRequestInFlight) return false;
+  return chat.titleGenerationPending || !chat.title?.trim();
+}