feat(files): share a folder by link — its page lists what is in it, plays a video above the list

A /watch link may now open one of its owner's own folders (migration 0108: folder_id beside job_id,
exactly one set; a folder's links go with it). The page shows what is in the folder when it is
opened, newest first: a video or a song plays in the same player a file link has, above the list,
each keeping its own resume point; a document only downloads, never opens as a page. A file moved
out stops opening through the link at its next request. Password, expiry and stream-only work as on
a file link; the unfurl names the folder and counts its files, never their names. Source folders
and the Hub cannot be shared.

The folder menu gets "Copy link" and "Share with a link…" (the Share dialog's link half); the rail
marks a folder a live link opens.

Two fixes in the Share dialog on the way: revoking the last link no longer mints a new one at once,
and the new-link form goes back to downloadable after making a link.

frontend/src/components/ShareDialog.dom.test.tsx

@@ -5,7 +5,7 @@
 // colour class outranks them (clsx does not merge Tailwind), so a password-protected link looked
 // unprotected and Revoke hovered neutral. They live on the ICON now; this pins them there.
 import { describe, it, expect, afterEach, beforeEach, vi } from "vitest";
-import { render, screen, cleanup } from "@testing-library/react";
+import { render, screen, cleanup, fireEvent, waitFor } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import type { ReactNode } from "react";
 
@@ -15,12 +15,30 @@ vi.mock("react-i18next", async (importOriginal) => ({
   ...(await importOriginal<typeof import("react-i18next")>()),
   useTranslation: () => ({ t: (k: string) => k, i18n: { language: "en" } }),
 }));
-vi.mock("./ui/Modal", () => ({ default: ({ children }: { children: ReactNode }) => children }));
-vi.mock("./confirmContext", () => ({ useConfirm: () => async () => false }));
-const h = vi.hoisted(() => ({ links: null as unknown[] | null }));
+vi.mock("./ui/Modal", () => ({
+  default: ({ title, children }: { title: string; children: ReactNode }) => (
+    <div>
+      <h2>{title}</h2>
+      {children}
+    </div>
+  ),
+}));
+vi.mock("./confirmContext", () => ({ useConfirm: () => async () => h.confirm }));
+const h = vi.hoisted(() => ({
+  confirm: false,
+  revokeDownloadLink: vi.fn(),
+  links: null as unknown[] | null,
+  folderLinks: vi.fn(),
+  createFolderLink: vi.fn(),
+  createDownloadLink: vi.fn(),
+}));
 vi.mock("../lib/api", () => ({
   api: {
     shareRecipients: async () => [],
+    folderLinks: h.folderLinks,
+    createFolderLink: h.createFolderLink,
+    createDownloadLink: h.createDownloadLink,
+    revokeDownloadLink: h.revokeDownloadLink,
     downloadLinks: async () =>
       h.links ?? [
         {
@@ -53,6 +71,7 @@ import type { DownloadJob } from "../lib/api";
 afterEach(cleanup);
 beforeEach(() => {
   h.links = null;
+  h.confirm = false;
 });
 
 const iconClass = (button: HTMLElement) => button.querySelector("svg")?.getAttribute("class") ?? "";
@@ -106,3 +125,86 @@ describe("ShareDialog · a link whose address cannot be shown again", () => {
     expect(screen.getAllByRole("button", { name: "downloads.share.revoke" })).toHaveLength(2);
   });
 });
+
+describe("ShareDialog · a folder", () => {
+  const link = (id: number) => ({
+    id,
+    token: `f${id}`,
+    url: `/watch/f${id}`,
+    allow_download: true,
+    has_password: false,
+    expires_at: null,
+    view_count: 0,
+    created_at: null,
+  });
+
+  it("shares by link only, says what a folder link shows, and makes it for the folder", async () => {
+    h.folderLinks.mockReset().mockResolvedValue([link(4)]);
+    h.createFolderLink.mockReset().mockResolvedValue(link(5));
+    const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    render(
+      <QueryClientProvider client={qc}>
+        <ShareDialog folder={{ id: 7, name: "Friends" }} onClose={() => {}} />
+      </QueryClientProvider>,
+    );
+    expect(await screen.findByDisplayValue(`${window.location.origin}/watch/f4`)).toBeTruthy();
+    expect(h.folderLinks).toHaveBeenCalledWith(7);
+    expect(screen.getByRole("heading").textContent).toBe("downloads.share.folderTitle");
+    expect(screen.getByText("downloads.share.folderLinkHint")).toBeTruthy();
+    // No sharing with a user: "Shared with me" lists files, not folders.
+    expect(screen.queryByText("downloads.share.userSection")).toBeNull();
+
+    // A stream-only link, then the form is back at its default for the next one: downloadable.
+    fireEvent.click(screen.getByRole("button", { name: "downloads.share.newLink" }));
+    // The form's own checkbox, under the link rows' (each row has its own).
+    const allow = () => {
+      const boxes = screen.getAllByRole("checkbox", { name: "downloads.share.allowDownload" });
+      return boxes[boxes.length - 1]!;
+    };
+    fireEvent.click(allow());
+    expect((allow() as HTMLInputElement).checked).toBe(false);
+    fireEvent.click(screen.getByRole("button", { name: "downloads.share.createLink" }));
+    await waitFor(() =>
+      expect(h.createFolderLink).toHaveBeenCalledWith(
+        7,
+        expect.objectContaining({
+          allow_download: false,
+        }),
+      ),
+    );
+    expect(h.createDownloadLink).not.toHaveBeenCalled();
+    fireEvent.click(await screen.findByRole("button", { name: "downloads.share.newLink" }));
+    expect((allow() as HTMLInputElement).checked).toBe(true);
+  });
+
+  it("makes a link on opening with none, but never right after the last one was revoked", async () => {
+    h.folderLinks.mockReset().mockResolvedValue([]);
+    h.createFolderLink.mockReset().mockResolvedValue(link(6));
+    const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    const view = render(
+      <QueryClientProvider client={qc}>
+        <ShareDialog folder={{ id: 7, name: "Friends" }} onClose={() => {}} />
+      </QueryClientProvider>,
+    );
+    await waitFor(() => expect(h.createFolderLink).toHaveBeenCalledTimes(1));
+    view.unmount();
+
+    h.confirm = true;
+    h.folderLinks
+      .mockReset()
+      .mockResolvedValueOnce([link(4)])
+      .mockResolvedValue([]);
+    h.createFolderLink.mockReset();
+    h.revokeDownloadLink.mockReset().mockResolvedValue({ ok: true, deleted: 4 });
+    const qc2 = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    render(
+      <QueryClientProvider client={qc2}>
+        <ShareDialog folder={{ id: 7, name: "Friends" }} onClose={() => {}} />
+      </QueryClientProvider>,
+    );
+    fireEvent.click(await screen.findByRole("button", { name: "downloads.share.revoke" }));
+    await waitFor(() => expect(h.revokeDownloadLink).toHaveBeenCalledWith(4));
+    await screen.findByText("downloads.share.noLinks");
+    expect(h.createFolderLink).not.toHaveBeenCalled();
+  });
+});