android: a playlist's cover from a photo on the phone

The storage plugin gains pick_image — the document picker limited to
images, the picked content copied into the app's cache so the Rust side
gets a plain path. playlist_cover_set(id, path) is the desktop pick's
install step split out and shared (squared, the master cover, the row's
revision moved). A playlist's sheet offers Choose cover photo and Remove
custom cover; the mock walk exercises both.

src/lib/mockLibrary.js

@@ -93,7 +93,7 @@ let plSeq = 3;
 let plItemSeq = 100;
 const PL_T0 = 1_725_000_000;
 const PL = [
-    { id: 1, name: "Late night drive", track_count: 0, description: "Slow, wide, mostly synths.", kind: "manual", pinned: true, cover_path: null, created_at: PL_T0, updated_at: PL_T0, revision: 1, duration_secs: 0, unresolved_count: 0 },
+    { id: 1, name: "Late night drive", track_count: 0, description: "Slow, wide, mostly synths.", kind: "manual", pinned: true, cover_path: "mock://cover1", created_at: PL_T0, updated_at: PL_T0, revision: 1, duration_secs: 0, unresolved_count: 0 },
     { id: 2, name: "Boiler Room 2019", track_count: 0, description: null, kind: "setlist", pinned: false, cover_path: null, created_at: PL_T0 + 10, updated_at: PL_T0 + 10, revision: 1, duration_secs: 0, unresolved_count: 0 },
     { id: 3, name: "Empty one", track_count: 0, description: null, kind: "manual", pinned: false, cover_path: null, created_at: PL_T0 + 20, updated_at: PL_T0 + 20, revision: 1, duration_secs: 0, unresolved_count: 0 },
 ];
@@ -135,7 +135,9 @@ function mockLyrics(title) {
 function mockPlaylists(cmd, args) {
     if (cmd === "list_playlists") return Promise.resolve(PL.map((p) => ({ ...p })));
     if (cmd === "playlist_items") return new Promise((r) => setTimeout(() => r((PL_ITEMS[Number(args?.id)] || []).map((x) => ({ ...x }))), 80));
-    if (cmd === "playlist_cover") { const p = plOf(args); return Promise.resolve(p && (p.id === 1 || p.cover_path) ? svgArt(p.id === 1 ? 330 : 280, p.id === 1 ? "L" : "M") : null); }
+    if (cmd === "playlist_cover") { const p = plOf(args); return Promise.resolve(p && p.cover_path ? svgArt(p.id === 1 ? 330 : 280, p.id === 1 ? "L" : "M") : null); }
+    if (cmd === "playlist_cover_set") { const p = plOf(args); if (!p) return Promise.reject(new Error("no such playlist")); p.cover_path = String(args?.path || "mock://photo"); plTouch(p); return Promise.resolve(svgArt(300, "P")); }
+    if (cmd === "playlist_cover_clear") { const p = plOf(args); if (p) p.cover_path = null; plTouch(p); return Promise.resolve(); }
     if (cmd === "create_playlist") {
         const p = { id: ++plSeq, name: args?.name || "New Playlist", track_count: 0, description: null, kind: args?.kind || "manual", pinned: false, cover_path: null, created_at: Math.floor(Date.now() / 1000), updated_at: 0, revision: 0, duration_secs: 0, unresolved_count: 0 };
         PL.push(p);
@@ -516,6 +518,7 @@ function mockCatalog(cmd, args) {
     if (cmd === "plugin:storage|pick_folder") return Promise.resolve({ uri: "content://mock/tree/primary%3AMusic", path: "C:\\mock\\Music" });
     if (cmd === "plugin:storage|all_files_access") return Promise.resolve({ granted: true });
     if (cmd === "plugin:storage|request_all_files_access") return Promise.resolve();
+    if (cmd === "plugin:storage|pick_image") return Promise.resolve({ path: "C:\\mock\\photo.jpg" });
     if (cmd === "plugin:share|pending_share") {
         /* the harness shares by setting window.__ssMock.share and waking the page */
         const t = (typeof window !== "undefined" && window.__ssMock?.share) || null;