wallpaper: upscale a too-small staged image in place

A staged wallpaper smaller than its screen (yellow or red border) gets an
"Upscale 4x" button. It rewrites the file with Real-ESRGAN through
stable-diffusion.cpp's `sd-cli -M upscale`, keeping the name, so wallp's
state and the engine's lists, which name it by path, still find it.
sd-cli writes to a dot-named sibling the scan skips, and only a
successful run is moved over the original.

Success needs no [E] line as well as exit 0: with a model that fails to
load, sd-cli logs "[E] new_upscaler_ctx failed", saves the input
unscaled and exits 0 (measured).

The button takes two clicks so the model choice shows before anything is
rewritten. The first runs Imajev-4B, a small Jev-style vision decision
model, through llama-mtmd-cli on a 512 px thumbnail, with a grammar that
allows only A (anime) or B (photo or render); greedy decoding then
returns the higher-logit option, about 1.7 s. The label becomes
"Upscale 4x (anime)" or "(photo)", and the second click upscales with
the anime or the general model. Anything but A, including a failed
decider, picks the general model, safe on any image.

Imajev-4B was chosen by measurement on 22 wallpapers: all 12 anime and 4
photos right, 4 of 6 painted 3D renders called anime (those come out
smoother than painted). The 2B got 17 of 22, leaning to photo; a
three-way prompt adding "painted or render" dropped both to 15 or
fewer, with most anime called painted.

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

1 files changed, 30 insertions, 0 deletions

diff --git a/desktop/modules/appearance/WallpaperTab.qml b/desktop/modules/appearance/WallpaperTab.qml
index 640f1ef..134c90e 100644
--- a/desktop/modules/appearance/WallpaperTab.qml
+++ b/desktop/modules/appearance/WallpaperTab.qml
@@ -142,12 +142,42 @@ Column {
                 color: Wallpapers.qualityColor(subject, Wallpapers.target)
             }
 
+            Text {
+                width: parent.width
+                visible: Wallpapers.upscaleError !== ""
+                wrapMode: Text.Wrap
+                text: Wallpapers.upscaleError
+                font { family: Theme.fontFamily; pixelSize: Theme.fontSize - 4 }
+                color: Theme.red
+            }
+
             // A Flow, not a Row: a Row overflows its width and clipped the
             // last button in a narrow window (AGENTS.md).
             Flow {
+                id: actions
+                readonly property string staged: Wallpapers.target === "V" ? Wallpapers.pendingV : Wallpapers.pendingH
+                readonly property bool small: Wallpapers.canUpscale(staged, Wallpapers.target)
                 width: parent.width
                 spacing: 8
 
+                // Rewrite the staged image 4x larger before applying it, when
+                // it is too small for its screen. Two clicks: the first asks
+                // the decider which model suits it and shows the answer, the
+                // second upscales with that model (Wallpapers.decide and
+                // upscaleFile).
+                Tab {
+                    readonly property bool decided: Wallpapers.decidedFor === actions.staged
+                    readonly property bool busy: Wallpapers.deciding !== "" || Wallpapers.upscaling !== ""
+                    visible: actions.small || busy
+                    enabled: !busy
+                    text: Wallpapers.deciding !== "" ? "deciding…"
+                        : Wallpapers.upscaling !== "" ? "upscaling…"
+                        : decided ? `Upscale 4× (${Wallpapers.decidedKind})`
+                        : "Upscale 4×: pick model"
+                    selected: decided && !busy
+                    onClicked: decided ? Wallpapers.upscaleFile(actions.staged) : Wallpapers.decide(actions.staged)
+                }
+
                 // Apply and Reset are in the page header, with every settings
                 // page's.
                 // wallhaven-dl searches wallhaven.cc and finds larger