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/lib/downloads.test.ts

@@ -7,14 +7,19 @@ import { describe, it, expect, beforeEach, vi } from "vitest";
 import { QueryClient } from "@tanstack/react-query";
 
 // vi.mock is hoisted above these consts, so the mock fns must live in a hoisted block too.
-const { downloadLinks, createDownloadLink, copyText, notify } = vi.hoisted(() => ({
-  downloadLinks: vi.fn(),
-  createDownloadLink: vi.fn(),
-  copyText: vi.fn(),
-  notify: vi.fn(),
-}));
+const { downloadLinks, createDownloadLink, folderLinks, createFolderLink, copyText, notify } =
+  vi.hoisted(() => ({
+    downloadLinks: vi.fn(),
+    createDownloadLink: vi.fn(),
+    folderLinks: vi.fn(),
+    createFolderLink: vi.fn(),
+    copyText: vi.fn(),
+    notify: vi.fn(),
+  }));
 
-vi.mock("./api", () => ({ api: { downloadLinks, createDownloadLink } }));
+vi.mock("./api", () => ({
+  api: { downloadLinks, createDownloadLink, folderLinks, createFolderLink },
+}));
 vi.mock("./clipboard", () => ({ copyText }));
 vi.mock("./notifications", () => ({ notify }));
 
@@ -38,6 +43,8 @@ function qc() {
 beforeEach(() => {
   downloadLinks.mockReset();
   createDownloadLink.mockReset();
+  folderLinks.mockReset();
+  createFolderLink.mockReset();
   copyText.mockReset().mockResolvedValue(true);
   notify.mockReset();
 });
@@ -48,7 +55,7 @@ describe("quickShareLink", () => {
     createDownloadLink.mockResolvedValue({ id: 7, url: "/watch/tok7" });
     const openSpy = vi.spyOn(window, "open").mockReturnValue(null);
 
-    const url = await quickShareLink(qc(), { id: 42 }, t);
+    const url = await quickShareLink(qc(), { kind: "file", id: 42 }, t);
 
     expect(url).toBe(`${origin}/watch/tok7`);
     // Minted with an EMPTY body so the backend default (allow_download=true) applies.
@@ -65,7 +72,7 @@ describe("quickShareLink", () => {
   it("reuses an existing link instead of minting a duplicate", async () => {
     downloadLinks.mockResolvedValue([{ id: 3, url: "/watch/old" }]);
 
-    const url = await quickShareLink(qc(), { id: 1 }, t);
+    const url = await quickShareLink(qc(), { kind: "file", id: 1 }, t);
 
     expect(url).toBe(`${origin}/watch/old`);
     expect(createDownloadLink).not.toHaveBeenCalled();
@@ -78,7 +85,7 @@ describe("quickShareLink", () => {
       { id: 3, url: "/watch/older" },
     ]);
 
-    const url = await quickShareLink(qc(), { id: 1 }, t);
+    const url = await quickShareLink(qc(), { kind: "file", id: 1 }, t);
 
     expect(url).toBe(`${origin}/watch/older`);
     expect(createDownloadLink).not.toHaveBeenCalled();
@@ -90,7 +97,7 @@ describe("quickShareLink", () => {
     createDownloadLink.mockResolvedValue({ id: 8, url: "/watch/new" });
     const client = qc();
 
-    const url = await quickShareLink(client, { id: 6 }, t);
+    const url = await quickShareLink(client, { kind: "file", id: 6 }, t);
 
     expect(url).toBe(`${origin}/watch/new`);
     expect(copyText).toHaveBeenCalledWith(`${origin}/watch/new`);
@@ -100,11 +107,29 @@ describe("quickShareLink", () => {
     ]);
   });
 
+  it("a folder's link is the folder's own: listed, made and cached under the folder", async () => {
+    folderLinks.mockResolvedValue([]);
+    createFolderLink.mockResolvedValue({ id: 9, url: "/watch/fold" });
+    const client = qc();
+    client.setQueryData(qk.fileFolders(), []);
+
+    const url = await quickShareLink(client, { kind: "folder", id: 5 }, t);
+
+    expect(url).toBe(`${origin}/watch/fold`);
+    expect(folderLinks).toHaveBeenCalledWith(5);
+    expect(createFolderLink).toHaveBeenCalledWith(5, {});
+    expect(downloadLinks).not.toHaveBeenCalled();
+    expect(createDownloadLink).not.toHaveBeenCalled();
+    expect(client.getQueryData(qk.folderLinks(5))).toEqual([{ id: 9, url: "/watch/fold" }]);
+    // The rail's mark of a shared folder is asked for again.
+    expect(client.getQueryState(qk.fileFolders())!.isInvalidated).toBe(true);
+  });
+
   it("still toasts (warning) with the open action when the clipboard copy fails", async () => {
     downloadLinks.mockResolvedValue([{ id: 5, url: "/watch/x" }]);
     copyText.mockResolvedValue(false);
 
-    const url = await quickShareLink(qc(), { id: 2 }, t);
+    const url = await quickShareLink(qc(), { kind: "file", id: 2 }, t);
 
     expect(url).toBe(`${origin}/watch/x`); // the link is never a dead end
     const arg = firstToast();
@@ -117,7 +142,7 @@ describe("quickShareLink", () => {
     downloadLinks.mockResolvedValue([]);
     createDownloadLink.mockRejectedValue(new Error("boom"));
 
-    const url = await quickShareLink(qc(), { id: 9 }, t);
+    const url = await quickShareLink(qc(), { kind: "file", id: 9 }, t);
 
     expect(url).toBeNull();
     expect(copyText).not.toHaveBeenCalled();