wallpaper: a screen can draw from a gallery folder instead of its hearts

Every wallpaper in the gallery is wide, so hearting a whole folder one
thumbnail at a time is the long way to say "this folder". Each screen
now has a source on the engine page: its hearted list, or one gallery
folder picked by chip, stored as the Wallpapers.groups key in Prefs
(folderH, folderV, "" for the hearts).

A folder that has left the gallery gives an empty pool, so that screen
is left alone rather than quietly falling back to its hearts. The
hearted list stays saved behind a folder source and comes back with the
Hearted chip. Switching source needs nothing from the shuffle: draw()
already drops bag entries that are no longer in the pool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 14 insertions, 2 deletions

diff --git a/desktop/modules/appearance/WallEngine.qml b/desktop/modules/appearance/WallEngine.qml
index 9d90245..fe45f7b 100644
--- a/desktop/modules/appearance/WallEngine.qml
+++ b/desktop/modules/appearance/WallEngine.qml
@@ -31,6 +31,18 @@ Singleton {
 
     function list(which) { return which === "V" ? cfg.v : cfg.h; }
     function listed(path, which) { return list(which).indexOf(path) >= 0; }
+    // A gallery folder by its Wallpapers.groups key, "" for the hearted list.
+    function folder(which) { return which === "V" ? cfg.folderV : cfg.folderH; }
+    function setFolder(which, key) { Prefs.setWallEngine(which === "V" ? { folderV: key } : { folderH: key }); }
+    // What a tick draws from. A folder that is no longer in the gallery
+    // gives nothing, so that screen is left alone rather than falling back
+    // to the list behind the user's back.
+    function pool(which) {
+        const key = folder(which);
+        if (key === "") return list(which).filter(present);
+        const g = Wallpapers.groups.find(g => g.key === key);
+        return g ? g.files : [];
+    }
     // ponytail: present means in the gallery's last scan, so a file deleted
     // since stays drawable until a rescan, and wallp then skips it.
     function present(path) { return Wallpapers.files.indexOf(path) >= 0; }
@@ -64,8 +76,8 @@ Singleton {
     // A screen whose list is empty, or whose pick is already up, is left out.
     function tick() {
         if (Wallpapers.applying) return;
-        const h = Shuffle.draw(cfg.h.filter(present), bagH, Wallpapers.currentH);
-        const v = Shuffle.draw(cfg.v.filter(present), bagV, Wallpapers.currentV);
+        const h = Shuffle.draw(pool("H"), bagH, Wallpapers.currentH);
+        const v = Shuffle.draw(pool("V"), bagV, Wallpapers.currentV);
         const ph = h.pick !== Wallpapers.currentH ? h.pick : "";
         const pv = v.pick !== Wallpapers.currentV ? v.pick : "";
         if (Wallpapers.run(ph, pv, "tick")) {