feat(21-03): add chat API client, ChatPanelProvider, and TanStack Query hooks

- Create chatApi with full CRUD + archive/pin/message endpoints
- Create ChatPanelContext with localStorage persistence (nexus:chat-panel-open)
- Create useChatConversations with useInfiniteQuery and conversation mutations
- Create useChatMessages with useInfiniteQuery and useSendMessage
- Wrap app tree with ChatPanelProvider in main.tsx

ui/src/api/chat.ts

@@ -0,0 +1,37 @@
+import type { ChatConversation, ChatConversationListResponse, ChatMessage } from "@paperclipai/shared";
+import { api } from "./client";
+
+export const chatApi = {
+  listConversations: (companyId: string, opts?: { cursor?: string; limit?: number }) => {
+    const params = new URLSearchParams();
+    if (opts?.cursor) params.set("cursor", opts.cursor);
+    if (opts?.limit) params.set("limit", String(opts.limit));
+    const qs = params.toString();
+    return api.get<ChatConversationListResponse>(`/api/companies/${companyId}/conversations${qs ? `?${qs}` : ""}`);
+  },
+  createConversation: (companyId: string, data?: { title?: string }) =>
+    api.post<ChatConversation>(`/api/companies/${companyId}/conversations`, data ?? {}),
+  getConversation: (id: string) =>
+    api.get<ChatConversation>(`/api/conversations/${id}`),
+  updateConversation: (id: string, data: { title?: string }) =>
+    api.patch<ChatConversation>(`/api/conversations/${id}`, data),
+  deleteConversation: (id: string) =>
+    api.delete(`/api/conversations/${id}`),
+  archiveConversation: (id: string) =>
+    api.post<ChatConversation>(`/api/conversations/${id}/archive`, {}),
+  unarchiveConversation: (id: string) =>
+    api.post<ChatConversation>(`/api/conversations/${id}/unarchive`, {}),
+  pinConversation: (id: string) =>
+    api.post<ChatConversation>(`/api/conversations/${id}/pin`, {}),
+  unpinConversation: (id: string) =>
+    api.post<ChatConversation>(`/api/conversations/${id}/unpin`, {}),
+  listMessages: (conversationId: string, opts?: { cursor?: string; limit?: number }) => {
+    const params = new URLSearchParams();
+    if (opts?.cursor) params.set("cursor", opts.cursor);
+    if (opts?.limit) params.set("limit", String(opts.limit));
+    const qs = params.toString();
+    return api.get<{ items: ChatMessage[]; hasMore: boolean }>(`/api/conversations/${conversationId}/messages${qs ? `?${qs}` : ""}`);
+  },
+  sendMessage: (conversationId: string, data: { role: string; content: string; agentId?: string | null }) =>
+    api.post<ChatMessage>(`/api/conversations/${conversationId}/messages`, data),
+};

ui/src/context/ChatPanelContext.tsx

@@ -0,0 +1,60 @@
+import { createContext, useCallback, useContext, useState, type ReactNode } from "react";
+
+const STORAGE_KEY = "nexus:chat-panel-open";
+
+interface ChatPanelContextValue {
+  chatOpen: boolean;
+  setChatOpen: (open: boolean) => void;
+  toggleChat: () => void;
+  activeConversationId: string | null;
+  setActiveConversationId: (id: string | null) => void;
+}
+
+const ChatPanelContext = createContext<ChatPanelContextValue | null>(null);
+
+function readPreference(): boolean {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    return raw === "true";
+  } catch {
+    return false;
+  }
+}
+
+function writePreference(open: boolean) {
+  try {
+    localStorage.setItem(STORAGE_KEY, String(open));
+  } catch { /* ignore */ }
+}
+
+export function ChatPanelProvider({ children }: { children: ReactNode }) {
+  const [chatOpen, setChatOpenState] = useState(readPreference);
+  const [activeConversationId, setActiveConversationId] = useState<string | null>(null);
+
+  const setChatOpen = useCallback((open: boolean) => {
+    setChatOpenState(open);
+    writePreference(open);
+  }, []);
+
+  const toggleChat = useCallback(() => {
+    setChatOpenState((prev) => {
+      const next = !prev;
+      writePreference(next);
+      return next;
+    });
+  }, []);
+
+  return (
+    <ChatPanelContext.Provider
+      value={{ chatOpen, setChatOpen, toggleChat, activeConversationId, setActiveConversationId }}
+    >
+      {children}
+    </ChatPanelContext.Provider>
+  );
+}
+
+export function useChatPanel() {
+  const ctx = useContext(ChatPanelContext);
+  if (!ctx) throw new Error("useChatPanel must be used within ChatPanelProvider");
+  return ctx;
+}

ui/src/hooks/useChatConversations.ts

@@ -0,0 +1,56 @@
+import { useInfiniteQuery, useMutation, useQueryClient } from "@tanstack/react-query";
+import { chatApi } from "../api/chat";
+
+export function useChatConversations(companyId: string | null) {
+  return useInfiniteQuery({
+    queryKey: ["chat", "conversations", companyId],
+    queryFn: ({ pageParam }) =>
+      chatApi.listConversations(companyId!, { cursor: pageParam as string | undefined }),
+    initialPageParam: undefined as string | undefined,
+    getNextPageParam: (lastPage) =>
+      lastPage.hasMore ? lastPage.items.at(-1)?.updatedAt : undefined,
+    enabled: !!companyId,
+  });
+}
+
+export function useCreateConversation(companyId: string | null) {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: (data?: { title?: string }) =>
+      chatApi.createConversation(companyId!, data),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ["chat", "conversations", companyId] });
+    },
+  });
+}
+
+export function useConversationActions() {
+  const queryClient = useQueryClient();
+  return {
+    pin: useMutation({
+      mutationFn: chatApi.pinConversation,
+      onSuccess: () => queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] }),
+    }),
+    unpin: useMutation({
+      mutationFn: chatApi.unpinConversation,
+      onSuccess: () => queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] }),
+    }),
+    archive: useMutation({
+      mutationFn: chatApi.archiveConversation,
+      onSuccess: () => queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] }),
+    }),
+    unarchive: useMutation({
+      mutationFn: chatApi.unarchiveConversation,
+      onSuccess: () => queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] }),
+    }),
+    remove: useMutation({
+      mutationFn: chatApi.deleteConversation,
+      onSuccess: () => queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] }),
+    }),
+    rename: useMutation({
+      mutationFn: ({ id, title }: { id: string; title: string }) =>
+        chatApi.updateConversation(id, { title }),
+      onSuccess: () => queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] }),
+    }),
+  };
+}

ui/src/hooks/useChatMessages.ts

@@ -0,0 +1,26 @@
+import { useInfiniteQuery, useMutation, useQueryClient } from "@tanstack/react-query";
+import { chatApi } from "../api/chat";
+
+export function useChatMessages(conversationId: string | null) {
+  return useInfiniteQuery({
+    queryKey: ["chat", "messages", conversationId],
+    queryFn: ({ pageParam }) =>
+      chatApi.listMessages(conversationId!, { cursor: pageParam as string | undefined }),
+    initialPageParam: undefined as string | undefined,
+    getNextPageParam: (lastPage) =>
+      lastPage.hasMore ? lastPage.items.at(-1)?.createdAt : undefined,
+    enabled: !!conversationId,
+  });
+}
+
+export function useSendMessage(conversationId: string | null) {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: (content: string) =>
+      chatApi.sendMessage(conversationId!, { role: "user", content }),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ["chat", "messages", conversationId] });
+      queryClient.invalidateQueries({ queryKey: ["chat", "conversations"] });
+    },
+  });
+}

ui/src/main.tsx

@@ -9,6 +9,7 @@ import { CompanyProvider } from "./context/CompanyContext";
 import { LiveUpdatesProvider } from "./context/LiveUpdatesProvider";
 import { BreadcrumbProvider } from "./context/BreadcrumbContext";
 import { PanelProvider } from "./context/PanelContext";
+import { ChatPanelProvider } from "./context/ChatPanelContext";
 import { SidebarProvider } from "./context/SidebarContext";
 import { DialogProvider } from "./context/DialogContext";
 import { ToastProvider } from "./context/ToastContext";
@@ -48,11 +49,13 @@ createRoot(document.getElementById("root")!).render(
                   <BreadcrumbProvider>
                     <SidebarProvider>
                       <PanelProvider>
-                        <PluginLauncherProvider>
-                          <DialogProvider>
-                            <App />
-                          </DialogProvider>
-                        </PluginLauncherProvider>
+                        <ChatPanelProvider>
+                          <PluginLauncherProvider>
+                            <DialogProvider>
+                              <App />
+                            </DialogProvider>
+                          </PluginLauncherProvider>
+                        </ChatPanelProvider>
                       </PanelProvider>
                     </SidebarProvider>
                   </BreadcrumbProvider>