diff --git a/packages/views/chat/components/chat-input.test.tsx b/packages/views/chat/components/chat-input.test.tsx
index ee123e815..5342c16bd 100644
--- a/packages/views/chat/components/chat-input.test.tsx
+++ b/packages/views/chat/components/chat-input.test.tsx
@@ -321,6 +321,7 @@ describe("ChatInput attachment wiring", () => {
 
   it("does not render the file upload button when onUploadFile is omitted", () => {
     renderInput({ onUploadFile: undefined });
+    expect(editorProps.last?.onUploadFile).toBeUndefined();
     // FileUploadButton renders an icon button labelled by its tooltip — when
     // upload wiring is absent the chat input falls back to "submit + extras"
     // only. Probe by counting buttons: with no upload, only the submit
diff --git a/packages/views/chat/components/chat-window.tsx b/packages/views/chat/components/chat-window.tsx
index 703c8d0ac..1bb9cf18d 100644
--- a/packages/views/chat/components/chat-window.tsx
+++ b/packages/views/chat/components/chat-window.tsx
@@ -770,7 +770,7 @@ export function ChatWindow() {
         onSend={handleSend}
         restoreDraftRequest={restoreDraftRequest}
         onRestoreDraftConsumed={handleRestoreDraftConsumed}
-        onUploadFile={handleUploadFile}
+        onUploadFile={activeAgent ? handleUploadFile : undefined}
         onStop={handleStop}
         isRunning={!!pendingTaskId}
         disabled={isSessionArchived}
diff --git a/packages/views/chat/components/chat-window.upload-readiness.test.tsx b/packages/views/chat/components/chat-window.upload-readiness.test.tsx
new file mode 100644
index 000000000..4c47fd8e9
--- /dev/null
+++ b/packages/views/chat/components/chat-window.upload-readiness.test.tsx
@@ -0,0 +1,360 @@
+import { describe, expect, it, beforeEach, vi } from "vitest";
+import { fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { I18nProvider } from "@multica/core/i18n/react";
+import type { Agent, ChatSession } from "@multica/core/types";
+import type { UploadResult } from "@multica/core/hooks/use-file-upload";
+import enCommon from "../../locales/en/common.json";
+import enChat from "../../locales/en/chat.json";
+import enIssues from "../../locales/en/issues.json";
+
+const mocks = vi.hoisted(() => {
+  const chatState = {
+    isOpen: true,
+    isExpanded: false,
+    activeSessionId: null as string | null,
+    selectedAgentId: null as string | null,
+    setOpen: vi.fn(),
+    setActiveSession: vi.fn(),
+    setSelectedAgentId: vi.fn(),
+  };
+
+  return {
+    queryState: {
+      agents: [] as unknown[],
+      members: [] as unknown[],
+      sessions: [] as unknown[],
+      pendingTask: null as unknown,
+      availability: "loading",
+    },
+    chatState,
+    chatInput: {
+      lastProps: null as null | Record<string, unknown>,
+      fileCardsInserted: 0,
+    },
+    queryClient: {
+      setQueryData: vi.fn(),
+      invalidateQueries: vi.fn(),
+      cancelQueries: vi.fn(),
+    },
+    createSession: vi.fn(),
+    deleteSession: {
+      mutate: vi.fn(),
+      isPending: false,
+    },
+    markRead: {
+      mutate: vi.fn(),
+    },
+    updateSession: {
+      mutate: vi.fn(),
+      isPending: false,
+    },
+    uploadWithToast: vi.fn(),
+    fetchOlderMessages: vi.fn(),
+  };
+});
+
+vi.mock("motion/react", () => ({
+  motion: {
+    div: ({ children, initial: _initial, animate: _animate, transition: _transition, ...props }: any) => (
+      <div {...props}>{children}</div>
+    ),
+  },
+}));
+
+vi.mock("sonner", () => ({
+  toast: {
+    error: vi.fn(),
+  },
+}));
+
+vi.mock("@tanstack/react-query", () => ({
+  queryOptions: (options: unknown) => options,
+  infiniteQueryOptions: (options: unknown) => options,
+  useQueryClient: () => mocks.queryClient,
+  useQuery: (options: { queryKey?: readonly unknown[] }) => {
+    const key = JSON.stringify(options.queryKey ?? []);
+    if (key.includes('"agents"')) return { data: mocks.queryState.agents };
+    if (key.includes('"members"')) return { data: mocks.queryState.members };
+    if (key.includes('"sessions"')) return { data: mocks.queryState.sessions };
+    if (key.includes('"pending-tasks"')) return { data: { tasks: [] } };
+    if (key.includes('"pending-task"')) return { data: mocks.queryState.pendingTask };
+    return { data: undefined };
+  },
+  useInfiniteQuery: () => ({
+    data: {
+      pages: [{
+        messages: [],
+        limit: 50,
+        has_more: false,
+        next_cursor: null,
+      }],
+      pageParams: [null],
+    },
+    isLoading: false,
+    fetchNextPage: mocks.fetchOlderMessages,
+    hasNextPage: false,
+    isFetchingNextPage: false,
+  }),
+}));
+
+vi.mock("@multica/core/hooks", () => ({
+  useWorkspaceId: () => "ws-1",
+}));
+
+vi.mock("@multica/core/auth", () => ({
+  useAuthStore: (selector: (state: { user: { id: string } }) => unknown) =>
+    selector({ user: { id: "user-1" } }),
+}));
+
+vi.mock("@multica/core/agents", () => ({
+  useAgentPresenceDetail: () => "loading",
+  useWorkspaceAgentAvailability: () => mocks.queryState.availability,
+}));
+
+vi.mock("@multica/core/hooks/use-file-upload", () => ({
+  useFileUpload: () => ({
+    uploadWithToast: mocks.uploadWithToast,
+  }),
+}));
+
+vi.mock("@multica/core/chat", () => ({
+  useChatStore: (selector: (state: typeof mocks.chatState) => unknown) =>
+    selector(mocks.chatState),
+}));
+
+vi.mock("@multica/core/chat/mutations", () => ({
+  useCreateChatSession: () => ({
+    mutateAsync: mocks.createSession,
+  }),
+  useDeleteChatSession: () => mocks.deleteSession,
+  useMarkChatSessionRead: () => mocks.markRead,
+  useUpdateChatSession: () => mocks.updateSession,
+}));
+
+vi.mock("@multica/views/issues/components", () => ({
+  canAssignAgent: () => true,
+}));
+
+vi.mock("@multica/core/api", () => ({
+  api: {
+    cancelTaskById: vi.fn(),
+  },
+}));
+
+vi.mock("../../common/actor-avatar", () => ({
+  ActorAvatar: ({ actorId }: { actorId: string }) => (
+    <span data-testid={`avatar-${actorId}`} />
+  ),
+}));
+
+vi.mock("./chat-message-list", () => ({
+  ChatMessageList: () => <div data-testid="chat-message-list" />,
+  ChatMessageSkeleton: () => <div data-testid="chat-message-skeleton" />,
+}));
+
+vi.mock("./chat-resize-handles", () => ({
+  ChatResizeHandles: () => null,
+}));
+
+vi.mock("./offline-banner", () => ({
+  OfflineBanner: () => null,
+}));
+
+vi.mock("./no-agent-banner", () => ({
+  NoAgentBanner: () => null,
+}));
+
+vi.mock("./use-chat-context-items", () => ({
+  useChatContextItems: () => [],
+}));
+
+vi.mock("./use-chat-resize", () => ({
+  useChatResize: () => ({
+    renderWidth: 420,
+    renderHeight: 520,
+    isAtMax: false,
+    boundsReady: true,
+    isDragging: false,
+    toggleExpand: vi.fn(),
+    startDrag: vi.fn(),
+  }),
+}));
+
+vi.mock("./chat-input", () => ({
+  ChatInput: (props: {
+    onUploadFile?: (file: File) => Promise<UploadResult | null>;
+  }) => {
+    mocks.chatInput.lastProps = props as unknown as Record<string, unknown>;
+    return (
+      <button
+        type="button"
+        data-testid="mock-chat-upload"
+        disabled={!props.onUploadFile}
+        onClick={() => {
+          if (!props.onUploadFile) return;
+          mocks.chatInput.fileCardsInserted += 1;
+          void props.onUploadFile(
+            new File(["pdf"], "brief.pdf", { type: "application/pdf" }),
+          );
+        }}
+      >
+        Upload
+      </button>
+    );
+  },
+}));
+
+import { ChatWindow } from "./chat-window";
+
+const TEST_RESOURCES = { en: { common: enCommon, chat: enChat, issues: enIssues } };
+
+function makeAgent(overrides: Partial<Agent> & Pick<Agent, "id" | "name" | "owner_id">): Agent {
+  return {
+    workspace_id: "ws-1",
+    runtime_id: "runtime-1",
+    description: "",
+    instructions: "",
+    avatar_url: null,
+    runtime_mode: "local",
+    runtime_config: {},
+    custom_args: [],
+    visibility: "workspace",
+    status: "idle",
+    max_concurrent_tasks: 1,
+    model: "sonnet",
+    skills: [],
+    created_at: new Date(0).toISOString(),
+    updated_at: new Date(0).toISOString(),
+    archived_at: null,
+    archived_by: null,
+    ...overrides,
+    id: overrides.id,
+    name: overrides.name,
+    owner_id: overrides.owner_id,
+  };
+}
+
+function makeUpload(): UploadResult {
+  return {
+    id: "att-1",
+    workspace_id: "ws-1",
+    issue_id: null,
+    comment_id: null,
+    chat_session_id: "session-1",
+    chat_message_id: null,
+    uploader_type: "member",
+    uploader_id: "user-1",
+    filename: "brief.pdf",
+    url: "https://cdn.example/brief.pdf",
+    download_url: "https://cdn.example/brief.pdf",
+    markdown_url: "/api/attachments/att-1/download",
+    content_type: "application/pdf",
+    size_bytes: 3,
+    created_at: new Date(0).toISOString(),
+    link: "https://cdn.example/brief.pdf",
+    markdownLink: "/api/attachments/att-1/download",
+  };
+}
+
+function makeSession(overrides: Partial<ChatSession> = {}): ChatSession {
+  return {
+    id: "session-1",
+    workspace_id: "ws-1",
+    agent_id: "agent-1",
+    creator_id: "user-1",
+    title: "",
+    status: "active",
+    has_unread: false,
+    created_at: new Date(0).toISOString(),
+    updated_at: new Date(0).toISOString(),
+    ...overrides,
+  };
+}
+
+function renderChatWindow() {
+  return render(
+    <I18nProvider locale="en" resources={TEST_RESOURCES}>
+      <ChatWindow />
+    </I18nProvider>,
+  );
+}
+
+beforeEach(() => {
+  mocks.queryState.agents = [];
+  mocks.queryState.members = [{ user_id: "user-1", role: "owner" }];
+  mocks.queryState.sessions = [];
+  mocks.queryState.pendingTask = null;
+  mocks.queryState.availability = "loading";
+  mocks.chatState.isOpen = true;
+  mocks.chatState.isExpanded = false;
+  mocks.chatState.activeSessionId = null;
+  mocks.chatState.selectedAgentId = null;
+  mocks.chatInput.lastProps = null;
+  mocks.chatInput.fileCardsInserted = 0;
+  mocks.queryClient.setQueryData.mockClear();
+  mocks.queryClient.invalidateQueries.mockClear();
+  mocks.queryClient.cancelQueries.mockClear();
+  mocks.createSession.mockReset();
+  mocks.createSession.mockResolvedValue(makeSession());
+  mocks.deleteSession.mutate.mockClear();
+  mocks.markRead.mutate.mockClear();
+  mocks.updateSession.mutate.mockClear();
+  mocks.uploadWithToast.mockReset();
+  mocks.uploadWithToast.mockResolvedValue(makeUpload());
+  mocks.fetchOlderMessages.mockClear();
+  mocks.chatState.setOpen.mockClear();
+  mocks.chatState.setActiveSession.mockClear();
+  mocks.chatState.setSelectedAgentId.mockClear();
+});
+
+describe("ChatWindow upload readiness", () => {
+  it("does not expose PDF upload while activeAgent is unavailable", async () => {
+    renderChatWindow();
+
+    const uploadButton = await screen.findByTestId("mock-chat-upload");
+    expect(uploadButton).toBeDisabled();
+    expect(mocks.chatInput.lastProps?.onUploadFile).toBeUndefined();
+
+    fireEvent.click(uploadButton);
+
+    expect(mocks.chatInput.fileCardsInserted).toBe(0);
+    expect(mocks.createSession).not.toHaveBeenCalled();
+    expect(mocks.uploadWithToast).not.toHaveBeenCalled();
+  });
+
+  it("keeps PDF upload available after an activeAgent resolves", async () => {
+    const view = renderChatWindow();
+
+    expect(await screen.findByTestId("mock-chat-upload")).toBeDisabled();
+
+    mocks.queryState.agents = [
+      makeAgent({ id: "agent-1", name: "Multica", owner_id: "user-1" }),
+    ];
+    mocks.queryState.availability = "available";
+    view.rerender(
+      <I18nProvider locale="en" resources={TEST_RESOURCES}>
+        <ChatWindow />
+      </I18nProvider>,
+    );
+
+    const uploadButton = await screen.findByTestId("mock-chat-upload");
+    await waitFor(() => {
+      expect(uploadButton).not.toBeDisabled();
+      expect(mocks.chatInput.lastProps?.onUploadFile).toEqual(expect.any(Function));
+    });
+
+    fireEvent.click(uploadButton);
+
+    await waitFor(() => {
+      expect(mocks.createSession).toHaveBeenCalledWith({
+        agent_id: "agent-1",
+        title: "",
+      });
+    });
+    expect(mocks.uploadWithToast).toHaveBeenCalledWith(
+      expect.any(File),
+      { chatSessionId: "session-1" },
+    );
+    expect(mocks.chatState.setActiveSession).toHaveBeenCalledWith("session-1");
+  });
+});